Frequently Asked Questions

You can submit an order via this website, or by phone or e-mail. Remember to include your phone number and address (including country or origin), so we can contact you with any freight costs & details. Local import taxes or duties (if any) will be the responsibility of the purchaser.

Yes, alternatively payments can be made directly into our bank account.

We have lots of information regarding all of the products, and how to use them, on our Frequently Asked Questions webpage.

If your enquiry is more technical in nature, send us an email at info@capepotterysupplies.co.za 

We think our products are amazing and support exceptional, but we are also very proud that:

1. We are a network of businesses across Africa & Australasia and we harness this breadth to bring the best to our customers.
2. We not only retail, we also manufacture, which gives us a competitive edge and expertise in what we do.
3. We only automate if absolutely necessary, and use local people to support local communities.
4. We work hard to keep our overheads low, ensuring accessible & affordable products.
5. We sell in a variety of volumes to support hobby potters, right up to large Industry.
6. We seek, select and source only quality ingredients.
7. Our team has decades of experience and knowledge, which we're are happy to share.

Most of our products are manufactured onsite in our factory in Cape Town South Africa. 

However, some items are imported from suppliers from across the world. We also export across the world.

The raw materials and some items are purchased in bulk, to ensure we can create economies of scale & only use the best possible ingredients.

As a group of companies, we commit to ensuring modern slavery practices do not occur in our supply chain.

Cape Pottery Supplies Pty Ltd is proudly part of the 'Fired Up Kilns Group'.

The Fired Up Kilns Group is dedicated to utilizing its networks, purchasing power and manufacturing ability to support local communities by offering affordable and durable products & services.

The group currently includes five entities operating across Oceania (based in Australia) and Africa (based in South Africa).

Its easy, Click here to view our Safety Data Sheets

The first thing to get your head around is that your kiln is a working appliance in your studio, consider it more like a tool in your shed, than a piece of furniture in your lounge. 

From the first firing, bricks will begin to brown & crack, metal will stain and corrode and ware will inevitably cause damage. Despite aging from day one, a kiln should on average last about 10 years.

Your kiln is not like your kitchens oven, kilns reach extremely high temperatures, more than five times the maximum temperature of your oven! Although safe when used as intended, they are not a toy and if you're not the sort of person that reads manuals, you may be better suited to use a local firing service.

We often say; ‘If you’ve fired one kiln, then you’ve only fired one kiln’!

Each kiln is different, and most firings are different, therefore learning how it fires and getting the results you want is just as much part of the ‘artistry’ of pottery as the throwing, sculpting and glazing. It takes time, practice and experience.

A kiln is a relatively simple appliance with minimal moving parts. Problems usually stem from issues with moisture, electricity supply, programming, ventilation, loading, or ware, rather than the kiln itself.  However moving and electrical components of the kiln function in a very toxic environment and will need regular (2 yearly) checking & maintenance. Given a failure of a component part can occur at any time, monitoring a firing kiln (we recommend at least hourly) is essential to mitigate the potentially devastating impacts of an uncontrolled over-firing.

All clays and glazes release toxic and corrosive gases during firing. Ventilation is essential and if you think you’ve done enough, double it! These toxic gases will corrode metal quickly if ventilation & air movement around your kiln isn’t adequate and/or you are using certain clays and glazes.

Kilns expand and contract significantly with each firing due to the massive temperature changes. They are built to do this, bricks will get cracks to release the pressure and things work loose over time. This is all normal and some simple maintenance will help you get the best possible lifespan from your kiln.

Our kilns are a studio’s workhorse, and we build our kilns accordingly to ensure maximum functionality and affordability when used as per our instructions.

Here is a dedicated web-page for people who are new to owning and operating a kiln.

If you are after more information on all aspects of electric kilns, we highly recommend you read:

“The Electric Kiln” by Harry Fraser. 

&

"Electric Kiln Construction for Potters" by Robert Fournier.

Both are out of print, but you can sometimes get copies online or in second hand bookshops.

Selecting and purchasing a kiln can sometimes be a daunting task. To help alleviate this, here is our step-by-step guide to assist you in selecting a kiln to suit your needs.

Electric or Gas?

Electric kilns are much easier to operate and control compared to gas kilns. They are easier to install and can usually be placed in a location that would be unsuitable for gas kilns, given the emissions from gas burning kilns. Consequentially, more potters, glass studios, jewellers, dental technicians and small industrial companies use electric kilns.

Gas kilns are more flexible in terms of controlling the kiln atmosphere; you can decide on oxidation versus reduction firing (we never advise reduction firing in an electric kiln). They are also ideal for raku. Another benefit of gas kilns is that they are better suited to high temperature applications e.g. porcelain (temperatures in excess of 1300c).

How much power do I have available?

A key factor that is sometimes overlooked when deciding on a kiln is the power available to operate the kiln you are considering. Typically, most Australian homes are supplied with single phase 240V 60A electricity. The standard household power point is rated to 10A only. As a result only our smallest kilns can be plugged directly into a standard power point. All other kilns will require either an upgraded electrical power point, or alternatively be wired directly to your household power. This work must be undertaken by a registered electrician, and we always advise you seek the advice of an electrician so you can budget on the cost of providing appropriate power to your kiln. In general, kilns larger than 6 cubic foot / 175L will require the provision of three phase power.

Front-loading or top-loading?

Front-loading kilns are generally of sturdier construction that top-loaders, and they tend to be more durable and resistant to everyday knocks. These kilns are generally easier to load as there is no need to bend over to pack them. Most are placed on a stand to bring them to a suitable height (or alternatively placed on a sturdy bench). Their main disadvantage is that they are more expensive to build and lack the portability of top-loaders

Top loading kilns usually has a cylindrical firing chamber. They are often suited to smaller work areas as no space is lost when the lid is opened. All of our top-loading kilns are fitted with wheels to allow for easy movement – this can be useful if they need to be moved to a storage area when not in use. They are also cheaper to manufacture and easier to transport. They are loaded through the lid and therefore each shelf must be filled before the next shelf is positioned, you need to bend over to load and unload them, and they depend upon the internal insulating bricks for their rigidity. 

What is the right size for me?

When deciding on this don’t forget to make allowances for any planned increase in output as well as possible changes in the type of ceramics you are making.

To determine which size best suits you, consider the following:

• What type of products/art would you like to produce? Vases? Bowls? Plates?
• If you have large pieces, do you do this on the odd occasion, and could you fire them off site?
• Consider the quantities you wish to load in each firing.
• You will usually want to fire a fully loaded kiln to get maximum efficiency. Think about how long it would take you to fill your kiln.
• Kiln sizes are described in volume (Litres or Cubic Feet). This is a helpful conceptual reference, not an accurate description. A tall skinny kiln and a short squat kiln may both have exactly the same 'volume' but accommodate very different ware!

What kiln furniture will I need? 

The size of your products and how you intend to pack your kiln will determine how many shelves and props you will need for your kiln. Don’t forget to allow for these in your budgeting. We supply furniture kits suited to each of our kilns. We can adjust the kits to your specific requirements and individual items can be purchased separately.

Time to choose the kiln for you!

Now it's all up to you (and your finances of course!). We suggest you ready the FAQ below about 'How does the freight / delivery system work?' Remember, we are always happy to help and provide advice. 

ALWAYS read (and re-read) your kilns manual as that contains specific safety and operating requirements for your kiln. However, the following are some generic safety recommendations for when you fire your kiln:

• Never alter, interfere or attempt any repair work on your kiln’s electrical connections, there is the possibility of electrocution.
• There is a cut-off switch that cuts power to the elements when the lid / door is opened… never override this!
• Use your kiln on a firm flat service away from water and high humidity.
• Make sure there is a clearance zone around your kiln: A clearance of 40cm around and 100cm above large industry kilns. A clearance of 30cm around all smaller kilns.
• Ensure all combustible and flammable materials (curtains, plastic equipment, paper & general clutter) are nowhere near the kiln. 
• Never allow anything to rest against the kiln (including cords and wires) or put objects under or on top of your kiln.
• Ensure that there is always good ventilation in the area where the kiln is located to disperse any toxic fumes.
• Only allow people who know how to use the kiln to operate it.
• Keep the kiln in an area inaccessible to children & pets.
• Never leave a firing kiln unattended, there are multiple uncontrollable factors that can cause a kiln to overfire, your vigilance is the only reliable prevention.
• To avoid injury, never touch your kilns external casing, handles or get close to the spyholes.
• Avoid looking into a kiln above 400°C without UV and infrared eye protection.
• Always use appropriate protective clothing (apron, thermal gloves, eye protection) when working around a hot kiln. 
• Do not open the kiln until the end of the program and only once at a safe temperature (i.e. 50°C or less).
• Use heat resistant gloves to unload your kiln.

Yes & No. 

To avoid boring you with pages of details (single phase, three phase, current, volts etc), kilns require significant current to heat up, the larger the kiln, the more current it will require.

Except for the smallest of kilns, a kiln will require the use of an upgraded power point. Sometimes this is a very simple task, sometimes it can be a costly nightmare! We always advise that you seek the advice of a registered electrician to ensure that you have access to adequate power to allow your kiln to perform as it should.

Kilns should have a dedicated electrical circuit with 20%  additional capacity than what your kiln requires. Otherwise new elements or sharing the circuit with other devices may trip the breaker. 

Kilns need at least 230 volts under load (when the contactor clicks on). Your electrician should check this during installation to prevent firing issues. 

Install an RCD (Residual Current Breaker) on new circuits. Moisture in the kiln can trip a sensitive RCD because of hydrophilic bricks touching the elements.

The kiln you buy may be limited by your available power capacity, as inadequate power may result in your kiln being unable to reach higher temperatures, or take a very long time to do so!

We are available to advise you or your electrician. 

Yes, it important to monitor a kiln during the firing process. 

Safety should always be your paramount concern when working with kilns.

Kilns are not a ‘set & forget’ piece of equipment, they operate at extremely high temperatures and must be treated with the respect and awe that they deserve. Despite multiple safety features, your kilns component’s function in a corrosive environment with extreme temperature fluctuations and corrosive gases.

Just because your kiln has a controller that can regulate the firing process, periodic checks and supervision is still essential (we recommend at least hourly).

By monitoring the temperature in your kiln, you can make sure that it is progressing through the stages as you intended. This also allows you to adjust as needed to ensure you are getting the heatwork you expected (that’s why you need to be using cones!).

Keeping a close eye on your kilns firing allows you to identify issues early and take quick corrective action. Failure to monitor and act early when things don’t seem right may result in an over-firing and potential devastating damage to your kiln and its ware.

Although electric kilns themselves do not release toxic gases, the ware being fired in your kiln will! A variety of toxic and corrosive gases are released during firing as the organic material is burnt off.

What you fire determines the composition of the fumes, as certain clays, glazes, decorating products, decals and the like, produce a variety of different gases, including, carbon dioxide, carbon monoxide, chlorine, fluorocarbons, sulphur dioxide, nitrogen oxides and ozone. Heavy metals may also be released if the firing temperature is hot enough and the volatile metals are present.

Good ventilation and air exchange around your kiln is best practice for your health & wellbeing.

Always consider:

• Reduce the number of toxic gases – Consider what clays, glazes and other items you put in your kiln. 
• Exhaust the kiln – Consider installing an Orton Ventmaster to your kiln.
• Exchange the rooms air – Install a whirlybird roof vent to drag the room air outside.
• Generate air movement – Have a ceiling fan or pedestal fan blowing on the kiln throughout the firing.
• Dilute the gases – Locate the kiln in the largest possible space, avoid small, closed spaces and corners. Remember, ‘the solution to pollution is dilution’.
• Create Air flow - Open all available windows & doors, including in adjacent rooms to capture any breezes.
• Monitor Air Quality – Affordable air quality monitors can be purchased and installed in your studio, so you can assess the effectiveness of your interventions.

Water vapour is likely the most abundant gas, and if your ware is not fully dry, this moisture can be absorbed by the hydrophilic kiln bricks and cause electrical outage of your kiln!

Bunging your kiln means to put bungs into the peepholes and/or close the top vent with a vent tile or bung. Bunging a kiln helps stabilise & control the internal kiln atmosphere. 

Bungs allow your vents & spyhole to be either closed or open, while a vent tile allow for partial closures depending on your need.

Our ‘rules of thumb’ are:

When your kiln is heating:

Leave the bungs out until approx. 500°C to allow for the escape of moisture vapour, carbon & sulphur.

• After this temperature put the bungs in to seal the kiln, this helps to retain heat, prevent sudden temperature changes & reach your top temperature most efficiently.
• If you are using BRT Clay or Terracotta, we suggest leaving the kiln open for longer (until approx. 900°C) to allow for the larger volume of impurities to escape.
• For lower temperature lustre & decal firings, leave the bungs out for the duration to allow the toxic fumes to disperse.

When your kiln is cooling:

Leave your bungs in to allow the kiln to slowly cool naturally till at least 300°C (or ambient temperature is possible).

• Too sudden a cooling may result in thermal shock, cracking ware, crazing glaze & potentially damaging your elements.
• You can use the vent tile to partially open a vent to assist in a managed cooling down.

Corrosion of your kiln is sadly unavoidable. The cold-hot-cold cycle, plus all the water vapor and toxic gases (sulfur, fluorine, carbon, etc.) coming out of the clays and glazes all combine to create a very corrosive environment for metal. The only thing you can control is the rate at which it corrodes. 

In general, corrosion isn’t covered under warranty because it’s considered a normal part of a kiln’s life, and the speed or extent of corrosion is related to its use and location, not the kiln.

Although the types of clay and glaze used can have a big impact, the most common factor we find with sudden and extensive corrosion is that the ventilation and air movement around the kiln isn’t adequate to off-set the volume of corrosive gases being released.

What can I do to reduce corrosion?

• Reduce the amount of toxic gases – Consider what clays, glazes and other items you put in your kiln. Move to a lower temp with a longer soak, make heatwork work for you.
• Reduce the water vapor – Resist the temptation to not let you ware dry fully before firing. Haste makes waste!
• Exhaust the kiln – Consider installing an Orton Ventmaster to your kiln.
• Exchange the rooms air – Install a whirlybird roof vent to drag the room air outside.
• Generate air movement – Have a ceiling fan or pedestal fan blowing on the kiln throughout the firing.
• Dilute the gases – Locate the kiln in the largest possible space, avoid small, closed spaces and corners. Remember, ‘the solution to pollution is dilution’.
• Create Air flow - Open all available windows & doors, including in adjacent rooms to capture any breezes.
• Reduce environmental moisture – Store your kiln in an enclosed space and / or cover with a BBQ cover. Place moisture absorbing packs in the kiln when not being used. Even in a dry location, dew will form on the kiln if it is located outside.

High humidity or being near the sea all increase the risk of and speed of corrosion.

Brushing excessive corrosion with a wire brush and painting it with a high-temp anti-rust paint may help tidy up the look of your kiln.

Thankfully corrosion doesn’t hurt the performance of the kiln and shouldn’t impact on its 10 year average life expectancy. 

Fire bricks are light weight, have millions of air pockets, are quite fragile and have excellent insulating properties… which is why they are used so successfully in the manufacture of many kilns. During the brick manufacture, small particles are burnt out, which leave behind the essential holes and fissures. Theses may appear random and unsightly, but are an essential part of the kilns ability to insulate.

Like everything in the kiln, the bricks will expand and contract with the heating and cooling cycle. The small hairline cracks or fissures that appear after the 1st firing are therefore perfectly normal and are to be expected. When the kiln is hot and the bricks expand, all these cracks fill in as a way of dissipating the growing pressure. 

Not every brick or slab cracks right away, however it appears that all bricks in the kiln, especially the slabs, will crack eventually. Opening the kiln too early will increase the risk of bricks cracking. 

A kiln that has reached a very high temperature or often endures significant heatwork, may show signs of shrinkage, cracking and browning of the internal face of the bricks and element channels.

The good news is, that unless the cracks are structural, even the most severe cracking will not affect the firing performance of your kiln.

It’s good to remember that Kilns are not designed to be airtight, they need to move and breath throughout the firing process. Its normal to sometime see the glow from inside the kiln between the bricks.

Light insulating firebricks are super insulators, but they are very fragile and easily damaged. 

Every firing leads to a process of expansion and contraction – which invariably leads to cracks in the bricks. These are a normal part of a kilns life and allows it to expand & contract when fired and no way effects the functioning of your kiln.

Regular firing to temperatures more than 1270c with prolonged soaks (greater than 10 minutes) increases the amount of contraction or shrinkage. The manufacturer of firebricks (Morgan Refractory) accepts a 1 - 2% contraction in the bricks when used as designed.

However, things happen, and kilns aren’t immune to thermal or mechanical shocks! Therefore if a brick (or part thereof) has become loose, dropped, or fallen, it needs to be secured.

Using pins for repairs whenever possible (instead of lots of mortar) allows the bricks to expand and contract along the pin. Too much mortar limits the brick’s ability to expand during firing and can lead to further cracking and damage.

To repair a brick, follow these simple steps:

ALWAYS turn your kiln off and unplug it from the wall or switch off the power circuit before doing any maintenance.

You’ll need:

- Pliers.

- Brick pins (we can supply these, don’t use normal wire as it will melt!).

- High Temp Mortar if needed (we can supply a small amount of this on request).

1. Vacuum the affected area thoroughly to remove any foreign material, brick dust or small fragments of brick.
2. Secure the bricks in the desired position, using a pair of piers, push in a brick pin to lock the bricks back into its location.
3. Bending the tip of the pin 90° will ensure the pin grips the hot face surface of the brick wall.
4. If the brick has dislodged, apply a sparing amount of mortar to the affected exposed surfaces, then place the piece back in its location and pin as per above.
5. Wipe away any excess mortar or drips. Depending on the mortar type, it will turn white after its first firing (the colour is just so you know where it it!).
6. Make sure no mortar gets onto your elements and if it does, carefully clean it up.
7. Allow mortar to air dry for at least 24 hours, then fire the kiln using a ramp rate of 50°C hr until 300°C, then the ramp rate of your choice. Using a slow ramp will allow the moisture to be driven out slowly and the mortar to bond.

There is no benefit in attempting to mortar over normal expansion or contraction cracks. In fact, this often leads to further cracking and damage, as the mortar limits the brick’s ability to expand during firing.

This can be challenging as the causes may be multiple.

After lots of experience helping our customers, we suggest a systematic process of elimination, starting with a few of the more common things to consider, such as:

1. Could it be user error? Always double check the program you are running on your controller, make sure that someone hasn’t added an extra long soak or changed a value.

• Always double check the program and get a fresh set of eyes to also review. Refer to your controller manual.

2. Are you sure it’s not reaching temperature? The temperature of the controller display is less important than how your ware is looking! Cones are the only way to truly understand the heatwork happening in your kiln.

• If you haven’t used cones, it’s probably time to start. Refer to our FAQ’s on cones.

3. Could it be moisture? Brick kilns are made from special fire bricks that have millions of air pockets, which gives them their excellent insulating properties. However, this also makes them hydrophilic - they absorb moisture like a sponge. Moisture is conductive and can create an electrical short circuit. 

• Protect your kilns from ambient humidity, bad weather, dripping condensation and always dry your ware fully before firing.

4. Has your kilns limit switch disengaged? As your kiln heat’s up it begins to expand (above 600°c – 800°c) and if your door or lid is not securely latched closed, the limit switch may disengage. This is a safety feature that cuts power to the elements when the kiln thinks the door/lid has been opened!  

• Always ensure your limit switch is fully engaged, and the door/lid latched shut. Over time your kilns door/lid will need some adjustment of the mechanism to continue to fully engage the limit switch. Refer to the instructions in your manual.

5. Are your elements wearing out?  Element lifespans reduce quickly when frequently fire to high (stoneware) temperatures - estimated lifespans are often quoted on the 'optimistic' end of the scale! 

- Elements are also effected by the thickness of the wire used (often European and US kilns arrive with thinner wire) and how they are maintained (i.e. glaze spills and clay fragments not cleaned from the element channels will cause hot-spots and weaken your elements). 

- Older elements require more power & time to heat than they did when they were new.

• It might be time to purchase a new set of elements, you can find more info on this in our shop and FAQ page.

6. Has one bank of your elements stopped working? Burnt out elements can be caused by a glaze spill, broken ware in the channel, slumped coils, or a corroded electrical connection to the elements.

• Place a strip of white paper behind each bank of elements and fire the kiln to 150°C. Once cooled, check the papers as they should all have scorch marks.

7. Has the Thermocouple failed? If it has been pushed back into the wall of the kiln it tends to read cooler and therefore risks over firing (rather than not reaching temperature) and a failed thermocouple will normally have erratic temperature fluctuations.

• However, make sure it’s not covered in glaze and in the correct position.

8. Could it be your power supply? Voltage drop when the kiln is actively drawing power may stop it reaching temperature.

- Are you using an extension cord? They reduce the amount of power getting to your kiln.

- Have you moved your kiln recently? Not every power outlet has the same ability to draw the same voltage.

- Is another device being used at the same time, that is drawing a lot of your power?

- Is a new development or business in your area impacting on the available power on your supply?

- Are ageing elements drawing more power than they did when they were new… and you just don’t have enough power anymore?

• An electrician needs to measure the kilns power draw when its engaged (clicked on and actively heating) and the available power at its location.
• If you can’t resolve any of the above then it might be possible to wind new elements with a slightly higher amperage to overcome the voltage drop.

Don’t forget kilns are about heatwork, not just temperature. Consider firing lower with a longer soak to get the results you want… and always use cones!

If you’re still having problems, give us a call to discuss.

Kilns are not designed to be air-tight!

It is completely normal to see a glow or colour between the lid/door and the kiln wall during firing. The amount of heat loss is insignificant and will in no way affect the efficiency or firing ability of your kiln.

It is actually the various light spectrum's that you are seeing (ultraviolet short range & visible medium range).

The longer range infrared spectrum (or Infrared radiation) of light is normally experienced as heat, begins at 400°C and can cause eye damage. Therefore, like you wouldn't look at the sun, its wise to NOT look into a glowing kiln without PPE like a welder's glasses.

To calculate the cost of firing a kiln you will need to know the following:

1. The electricity consumption per hour of your kiln. This will be expressed in Kilo Watts (KW) and can be found on the specification plate attached to the kiln, as well as our specification sheets.
2. The cost of electricity per Kilo Watt Hour (KWH) and can be pfound on your account summary - e.g. R0.55c per kW.
3. The length of your firing cycle.

Lets assume your kiln has a consumption of 5.5KW and you want to fire to 1220c over a 9-hour cycle and your cost of electricity is R0.55c KWH, then the calculation is as follows:

Consumption (KW) x Cost (per KWH) x Firing Time (Hours) = Cost

Example: 5.5 (KW) X 0.55 (KWH) X 9 (Hrs.) = R27.23 per firing.

The above calculation is based on the passage of current through the elements 100% of the time. 

In a firing cycle, the current may only flow 60 - 75% of the time, so the above value would be a worst-case scenario, and the likely true cost about 25% less.

Amps, volts, watts, and ohms are the four basic concepts when trying to understand electrical systems. 

Like how water flows through a hose, electricity is the flow of electrons through a conductor (normally a wire). 

We’ll use a water and hose analogy to explain the concepts.

What Are Amps?

The ampere, or amp for short, is the measure for current. Current is the speed at which the electrons flow through an electrical circuit. You might see amps if you look inside your home's meter box. You'll see different circuit breakers, like 15 amps, 20 amps and 30 amps. The larger the amperage, the more electricity can flow through the circuit.

If you try to run too many appliances on the same circuit, the breaker will "trip" and cut off power to protect the wiring from overheating.

In our water analogy, amps are equivalent to the amount of water flowing through the hose.

What Are Volts? 

Volts is the measure for voltage. Voltage is the difference in electrical potential, or the number of electrons, between any two points in a circuit. Australian electricity runs on 220 – 240 volts, while NZ runs on 230 – 240 volts.

In our water analogy, voltage is equivalent to water pressure. Pressure is the force that moves the water through the hose, just like voltage pushes electrons through a conductor. 

What Are Ohms? 

Ohms are the measure for resistance in a conductor (wire). Resistance tries to slow down the flow of electrons. As our circuits are made up of wires and these wires have a certain amount of natural resistance or friction, this all adds to slowing down the flow of electricity. Therefore, long distances of wire, extension cords and power banks all apply additional resistance.

In our water analogy, resistance is the diameter of the hose. A wide hose has very little resistance and allows water to flow through it quickly, while a narrow hose slows down the water.

What Are Watts?

Power is the rate at which electrical energy is transferred in a circuit and is measured in watts. This is electricity at work and indicates the power it takes to actually do something, whether it's running a vacuum (400 to 900 watts), ringing the doorbell (2 to 4 watts) or illuminating a light bulb (40 to 75 watts).

In our water analogy, power is a little harder to explain. With a hose, you can increase the power by either increasing the amount or the pressure of the water coming out. In an electrical system, you can increase the amps or the voltage.

A kiln element is a piece of wire that is designed to resist the passage of electricity. As current flows down the wire, the resistance impedes the flow and so causes the wire to heat up. Element lifespan is primarily dictated by the temperature to which you fire. The higher the temperature, the shorter the lifespan. 

As a rule of thumb Kanthal A1 elements will last about 500-600 firings to 1150c, 200-250 firings to 1220c, 120-150 firings to 1280c and no more than 75 to 1300c (1300c being the absolute maximum safe operating temperature of our kilns). These numbers come from Graph 1. In “Electric kiln construction for Potters” by Robert Fournier – a great book to read if you are a kiln freak! (I think they are a bit optimistic!) They are a probably best case scenarios and are meant as a guide. They assume that elements just wear out and not damaged. 

Unfortunately, impact to the elements in packing, glaze splatter or noxious gases will shorten the lifespan dramatically. You may notice that as your elements age, the kiln fires more slowly or struggles to get to temperature. This is a known characteristic of Kanthal wire. It is vital that you keep the element channels always clear of debris – a small piece of broken kiln brick or broken pot that jams up against an element can cause a local “over-heat” and burn out an element. Similar situations can occur with kiln wash or glaze getting onto the elements, always ensure your ware is bone dry. 

Our recommendation is that you carefully vacuum out all element channels before each firing and place glazed ware a minimum of 4cm from the elements – a little bit of care can make a big difference. An important feature of Kanthal wire is that after firing the wire will build up a layer of Aluminium oxide on its surface that protects it from attack by harmful gases. It will take 2-3 firings for this layer to build up. It is not a bad idea to therefore perform a couple of bisque firings with new elements (either a new kiln or replacement elements) prior to a glaze firing. The reason for this is that glazes will tend to liberate significantly more corrosive gas than does bisque ware. 

We NEVER recommend reduction firing in an electric kiln

Elements leaving their channel over time is not uncommon. Cold elements are brittle, however when red hot they become soft, so if the element has slowly moved, gravity can take over and the hot element can begin to sag.

Looks can be deceiving, elements that are sagging, stretched or misshapen may be unsightly, but they may still be functioning fine. You can use a multi-meter to check their condition (a +/- 10% variance from the elements normal is a sign replacement may be needed soon). 

Once an element leaves the wall of the kiln, they are not only at risk of being broken during loading, unloading but can also take up valuable space in your kiln. Therefore, if the element is still in good health, then repair may be worth a try before splashing out on replacement elements!

Before doing any maintenance on your kiln, you must consider safety:

• Consider ventilation, flammable materials, appropriate personal protective equipment.
• ALWAYS turn your kiln off and unplug it from the wall or switch off the power circuit.

Re-seating elements:

You’ll need:

• Needle nose pliers.
• Small blow torch (you can buy these at your local hardware shop).
• Element pins (we can supply these, don’t use normal wire as it will melt!).

1. Gently vacuum out the kiln and element channel. 
2. Remove any element pins you find in the empty channel (you can reuse them).
3. Use the blow torch to heat (turns red) the length of sagging element plus a few centimeters each side. The whole length may not be red all the time, but by sweeping back & forth you know it’s hot and less brittle.
4. Taking your time and alternating between both ends, while the element if glowing hot use the pliers to gently reshape and reposition the element.
5. Check that no coils of the element have become pinched together. If so, simply re-heat and stretch out the coil as necessary.
6. Once you’re happy its back in shape/place, use the blow torch to re-heat the entire element your worked back to glowing hot one last time.
7. Once cooled, gently use the pliers to push the element pins in to keep the element in place.

A video of someone explaining their technique can be found here.

To work out if one of your element banks isn't working, a paper test is a quick and easy 1st step.

1. Turn off and unplug your kiln.
2. Fold up small strips of paper, enough for each bank or run of elements.
3. Open you kiln and insert in between the element coils.
4. Close lid / door and turn your kiln on
5. Run a program and wait for the kiln to begin to heat (a few minutes).
6. Turn the kiln off and unplug.
7. When cool enough open the kiln and inspect the pieces of paper, if the elements heated, there should be scorch marks on the paper.

A video of our Partners at L&L Kilns explaining their technique can be found here.  (But unlike them, your kiln won't heat with the lid or door open - this protects you from electrocution).

This quick method helps determine if elements or relays need replacing  by observing which paper strips burn when inserted into the kiln's  elements during a test firing. 

If a single element's paper doesn't burn, it suggests a wiring issue or a broken element. If paper in an entire ring doesn't burn, it could indicate multiple burnt-out elements, a faulty relay, or a controller issue. The paper test is a starting point for troubleshooting your kiln.

Unless it's a kiln purchased through us, or one that is known to us, you'll need to send through a detailed drawing with the following information:

1. If a specification plate is visible, notate the current drawn, kW rating and voltage of the kiln. Also the model or serial number if available.
2. length of the elements and the number of grooves it occupies.
3. Indicate whether tails are twisted or single and the length.
4. Measure the outside diameter of the coils.
5. Measure the thickness of wire – use a vernier for accuracy, as the nominal difference between wires can be 0.1mm.

We wind our own elements and can typically have them made within a few days of a confirmed order, assuming you have provided all of the required information.

1. Safety is the first concern. Either unplug the kiln or isolate on the wall and also on the mains distribution board. If a locking device is provided, lock the switch off. In a domestic environment, advise the family of what you are doing, in particular to the switches that have been turned off.
2. All kilns are different, so these are general instructions only.
3. Your new elements should arrive stretched with segment elbows in place. 
4. Remove the covers exposing the connections to the elements. Elements are manufactured to ensure the correct amperage, therefore they should never be cut and only used as supplied.
5. Make a careful note of how the elements are connected (take a photo with your phone) and then disconnect all the wires to the tails of the elements, marking them appropriately for the positions to which they were attached. 
6. Old elements tend to  become very brittle and will probably break once you attempt to remove them from the grooves. Special care must be taken to protect the grooves in the bricks from being damaged.
7. Place the new element gently into the grooves to assess the fit – the element must be “seated” well into the groove – this may require removing the element during the fitting process to stretch it a bit more – make sure you stretch along the length of a segment to get an even stretch over the segment length. Sometimes you may need to squeeze the element coils closer together if the element is too long. There should be a smaller vertical groove in the brick between each large horizontal groove, this is where you will fit the segment elbow. 
8. If the elements were pinned previously then it would be recommended that you also pin the new elements in similar positions. Generally, 5-6 pins are used per segment. Use a pair of pliers to hold the pins firmly and then push them into position – avoid using the previous element pin positions.
9. You  will need a bolt cutter to trim the tails of the elements, which are  normally supplied over-length. Cut them to the same length of the old ones. 
10. Re-attach all your wires making sure that you fasten the wires to the element tails very firmly as a loose connection can cause a 'hot joint' and impact your kilns functioning.
11. If you are equipped to check the 'current draw' or if you have a friend who is, it's a good idea to compare the specified current versus the elements that have just been replaced. 
12. Replace all the covers. 
13. Then you may need to oxidize the elements – this is achieved by firing the kiln empty to 1100ºC and soaking for 3 hours with the bungs open. This process ensures that the elements generate an oxide layer, which  protects them from the atmosphere. 
14. If you do not feel confident in fitting an element we strongly recommend that you engage a kiln technician to change your kiln elements.

Some thermocouples have an extremely long life and are very expensive due to the rare metals used. Others have a much shorter life and are much more affordable. For example, the common K-Thermocouple is considered a consumable and its lifespan depends on a few factors, but mostly temp. For example a K-type may last 150 cone 06 firings, but only 50 cone 6 firings.

Thermocouples only read from the very tip, therefore if the tip isn’t full in the kiln, or sitting inside the brick canal, then it will read that locations cooler temperature, and mistakenly keep heating your kiln as it believes its not reaching temperature. This can cause your kiln to be destroyed by the overheating.

Similarly, if the thermocouple tip is too close to ware or a shelf, or covered in glaze, then it may read hotter than the  temperature inside the kiln. Resulting in under firing.

Electronic controllers are set according to your thermocouple type. If you change the type of thermocouple, then you will need to change the controller settings, so it knows which thermocouple it is trying to read. Otherwise the actual temperature in the kiln may be less or more than what the controller states. The higher the temperature in the kiln, the greater the variance and risk to your kiln. 

Because it’s reading such minute changes in electrical current, the leads that connect your thermocouple are often specific to the type of thermocouple. Make sure you use the correct leads / connecting wires.

If you accidentally reverse or swap the leads that connect your thermocouple, the polarity is swapped and the temperature shown will move in the opposite direction relative to the ambient temperature. I.e. when the kiln is getting hotter, it will show the kiln getting cooler.

The colour coding of the wires that connect your thermocouple are unique to each type of thermocouple and are often different to the electrical standards general electricians follow (the thermocouple measures microvolts across an electromotive junction). Ensure you or your electrician follows the installation instructions carefully to prevent incorrect wiring.

If the temperature on your controller is jumping around wildly (I.e. -30°C one moment and the 678°C the next), this is the sign that the fusion joint at the tip of the thermocouple, as a result of the wire becoming brittle after multiple firings (similar to your elements) has fractured. Do not use your kiln and contact us to get a replacement.

To changing a K-type thermocouple:

1. Ensure your kiln is either unplugged or turned off from the power point and/or the isolator switch and the breaker is in the OFF position.

2. Remove the terminal cover to expose the electrical connections in the kiln. The thermocouple will have a yellow 2-flex cable, containing a yellow (+) and a red (-) inner cables. Connected to the ceramic terminal block on the thermocouple.

3. Withdraw the ceramic connector (the thermocouple is connected to it). Check that the new thermocouple is no shorter than the failed thermocouple – this will ensure it sits a suitable distance into the kiln. Unscrew the connections of the compensating lead to the old thermocouple and insert the new thermocouple into the kiln.

4. K-type thermocouple polarity is:

POSITIVE (+) - YELLOW cable

NEGATIVE (-) - RED cable

5. Make sure your connection in the insulator block of both the red and yellow inner cables is solid.

6. IMPORTANT - Replace the terminal cover ensuring that all cables are both AWAY from the kiln case (minimum 1cm) and not trapped between the terminal cover and the base of the terminal box or between the terminal cover and the kiln case. This is critical as if the compensating lead contacts the kiln wall, then the potential exists from aberrant readings to occur as the kiln case heats up.

7. Turn your kiln on and run a program ensuring that the temperature in the kiln is increasing. If you notice a reduction in temperature, please stop the cycle and contact us. If the controller shows ‘OPEN’ or E000 then it indicates a loose connection.

Repeat steps 1-7 and check for faulty connections or breaks.

A thermocouple is the sensor in your kiln used to measure the temperature. They consist of two wire legs made from different metals, which are welded together at one end creating a junction. This junction (or tip) is where the temperature is actually measured. When the junction experiences a change in temperature, a voltage is created which can then be read by your controller. There are Multiple types:

• Best accuracy of common thermocouples, often used for food monitoring and environmental applications.

At the centre of your kiln's electrical system sits the contactor, an essential component that manages the flow of electricity to the elements. This switch opens and closes its contacts in response to signals from your kiln’s controller. This is the noise (click) you hear intermittently when your kiln is firing.

Its primary function is to ensure that electricity flows to the heating elements when the kiln needs to heat up and off when it’s time to hold a temperature. 

There are two basic designs of contactors, electromechanical and solid state.

Solid state contactors regulate the inflow of electrical energy by means of semiconductor factors, while electromechanical contactors depend on a physical contact to turn the circuits on or off.

Solid State contactors are faster, last longer, quieter and require less maintenance due to no moving parts. However, they are more expensive to initially purchase & install. 

Electromechanical contactors are the only moving part in your kiln, so wear and tear is an inevitable consequence of their repetitive mechanical action and the high electrical loads they manage. 

This is a bit of an impossible prediction as it really depends on usage, firing temperature, firing profile, corrosive environment and kiln care.

However, as a guide to help you work out when you should get your contactors checked or replaced, the following information may assist.

Contactors, in the ideal environment, should last around 200,000 cycles, with the average firing of your kiln requiring the contactor to engage at least 1000 cycles.

Therefore, it would be wise to get them reviewed or replaced after 200 firings.

Unfortunately, even the best, most expensive contactors can fail, long before this prediction, and without any warning or explanation!

This is why there is no escaping it… you must monitor a firing kiln at least hourly to ensure a contactor has not failed and is stuck in the ‘on’ position! 

Although thankfully rare, if this occurs, the kiln will continue to heat until the elements burn out. This will result in the destruction of your ware and potentially extensive damage to the inside of your kiln.  

There are few simple rules that you should follow to ensure you get the very best life from your kiln furniture.

1. Store your kiln shelves on their end. Never flat and certainly never stacked on top of each other. Doing so significantly increases the risk of shelves cracking.
2. Use kiln wash to minimise the risk of glaze runs sticking to a shelf. Regularly scrape off and reapply your kiln wash.
3. Flip kiln shelves when using them in the kiln to minimise warping. All shelves will begin to warp, faster at temperatures exceeding 1260c. The thicker the shelves the less they warp but this can make them harder to load due to the weight of the shelf. The best solution is to use shelves that you can handle easily and regularly flip them (every 5 - 6 firings). 
4. If the underside of a shelf has left over kiln wash on it, then you risk having flakes of kiln wash drop onto your glazed ware below, causing damage. Use a rub brick to clean the kiln wash off.
5. Make sure you kiln shelves are bone dry before use. If there is moisture in the shelves, then as they heat, they are likely to crack. Shelves are cut using a water blade, so new shelves may be damp. If in doubt, candle at 90°C for a few hours.
6. Use moderate ramp rates in the initial stages of the firing up until 200c (generally rates below 120c/hr are safe). Fast ramp rates can cause rapid expansion and shelf cracking. The same applies when cooling your kiln, avoid thermal shock from rapid cooling by never opening your kiln when its above 100°C.
7. Use 3 props to support a shelf as this is the most stable configuration. Ensure the props are placed in line vertically, so that the load of each shelf is passed down through the props.
8. Check your shelves carefully when packing your kiln. If a shelf is showing signs of cracking DON’T use it. You are better off replacing a suspect kiln shelf than having a collapse of furniture and ware in the kiln.

Kiln shelves do not last forever, but by following the above guidelines you will help prolong their life. The higher you fire, the more likely you are to experience warping and cracking of your shelves even with the best of kiln shelf care.

To get a detailed comparison between the differing shelves, have a look at the handy comparison guide our partners at Fired Up Kilns have created.

The differing types include:

1. Cordierite-Mullite: A low-expansion magnesium-aluminium-silicate refractory formed by heating a mixture of talc, clay, and mullite to about 1350°C
2. Perforated Cordierite-Mullite: As per above but has multiple holes punched out of the shelf, reducing its weight & thermal mass.
3. Hollow Cordierite-Mullite: As per above but is thicker and has hollow tubes within the shelf, reducing its weight & thermal mass.
4. Silicon Carbide Shelves: Including silicon carbide makes the shelves stronger and withstands higher temps. Can therefore be made thinner and as a result lighter. Also takes up less space in the kiln & a reduced thermal mass equals greater energy efficiency. There are a few types, each has differing properties and costs.

• Oxygen Bonded Silicon Carbide (OBSiC).
• Nitrogen Bonded Silicon Carbide (NBSiC).
• Recrystalized Silicon Carbide (RSiC).
• Sintered Silicon Carbide (SSiC) - the newest & thinnest.

Mix up some kiln wash with water until it is the consistency of milk. Its better to make it too runny than too thick, otherwise it might crack off your shelf before you even put your shelves in the kiln! 

Brush this runny mixture onto only one side of your kiln shelf with a soft brush and allow to dry. You will still see some of the shelf colour through the kiln wash. Apply a 2nd coat to the shelf and allow it to dry. You may need to apply a third coat.

You will know when you have applied enough when you can no longer see the colour of the shelf through the kiln wash and your shelf appears white. Once you have done this, leave your shelves to dry overnight.

The shelves will have soaked up water with each application of kiln wash, and you don't want to fire damp shelves in the kiln as they may crack. Therefore, fire your shelves 1st in a bisque firing – i.e. fire them slowly, rather than  fast. 

That way you will be able to use your shelves for many firings - up until the kiln wash starts to crack off the shelves (10 - 20 firings if you look after them). When needed, scrape it off the old kiln wash (we have Rub Bricks to help with this), turn your shelf over, and apply new kiln wash to the other side of the shelf.

Flipping your shelves periodically helps prevent them from sagging.

If you apply kiln wash to the underside of your shelves, or don't remove old kilns wash once you flip a shelf, when it starts to peel off it may fall on your pieces in a glaze firing!

Kiln forming techniques require separators between the glass and the shelf or mould on which it rests during the heating process. These separators have different generic names - kiln wash and batt wash are two.

There are a number of brands of kiln wash. All of them contain two main ingredients - alumina hydrate (sometimes called slaked alumina) and kaolin (also called china clay). Different producers use these ingredients in various proportions. A number also include a colourant that changes when fired above certain temperatures to indicate the material has been dried.

An important thing to remember is that the kaolin changes its composition once it is fired over 700C. This change causes it to stick to the glass on subsequent firings. Thus, it is essential to change the kiln wash after every firing that reaches that temperature or higher.

It is possible to apply a fresh coat of kiln wash over the old one to save time. However, as soon as the kiln wash flakes you must scrape off all the old kiln wash and apply a new coat to the bare shelf or mould.

By Stephen Richard

You often use more than one shelf when packing a Raku kiln.

When the time comes for removing the fired items while still red-hot, tongs are used. 

In order to remove a shelf quickly with tongs, holes are made in the shelf to allow the tongs to grip the shelf easily.

The two important things to fully understand are HEATWORK & CONES.

Mastering your kiln goes beyond relying on the controller to measure temperature and time alone. Success involves understanding the kiln itself, its unique characteristics and nuances in heat distribution and heatwork. 

This knowledge enables informed decisions and adjustments, blending technical precision with a nuanced understanding of the kiln's behaviour and performance to achieve the firing results you want.

Firing ceramics in a kiln is a bit like cooking. You can set your oven on a very high heat and cook your dinner in just a few minutes, or you can cook it for longer at a lower heat. Either way, you end up with a cooked dinner.

Heatwork is the combination of time and temperature. Our imaginary dinners received the same amount of heatwork, even if they were cooked at different temperatures and for different durations.

Pyrometric Cones are still a very important tool in a potter’s armoury and the only definitive measure of heatwork. 

Without a cone in your kiln you will not know whether your pottery reached temperature unless it is badly under fired. It is useful to bench mark good firings with cones and to save these results.  If you are experiencing unsatisfactory results, cones will quickly tell  you whether the kiln or glaze is at fault. 

• If the fired results of cones significantly differ to your benchmark, then look to your kiln for the cause. 
• If the fired result of the cones is the same as your benchmark, look to your glazes and or clay body for the cause. 

It is useful to place cones next to your thermocouple and in areas where you get your best results, as these are your litmus tests.

Our created a quick reference guide may be helpful.

Thermocouples only measures temperature, and they do so only in the immediate vicinity of the junction (tip). Pyrometric cones measure “heat work” – which is a measure of the impact of time and temperature.

1. Cones consist of a mixture of carefully controlled ceramic materials that are designed to give a graduated scale of fusing temperatures. The most commonly available cones are manufactured by the Orton company, and they provide a chart that provides the fusing temperature with a corresponding cone number.
2. Orton Cones are frequently shipped in "Compacts" (2 Connected Cones) to improve stability and prevent damage. These cones need to be separated before use by gently snapping them apart. A video of how to do this is here.
3. Cones are mounted either in a specific refractory cone holder or alternatively embedded in a wad of clay, with each cone placed to the same depth and at an angle of 15° to the vertical. This is assisted by a slant on the base of the cone.
4. A series of three cones is standard, the cone placed on the far left indicates 20° below the required temperature, the middle cone indicates the required temperature and the cone to the right indicates a temperature 20° above the required temperature. The collapse of the first cone serves as a warning that the required temperature is being reached, whilst the second cone collapse indicates the correct temperature. The third cone, or “guard” cone should remain upright as it serves to warn of potential over firing. The fusion point of any cone is indicated when the tip of the cone touches the base on which the cone is mounted.
5. It is a good idea to place cones in several locations in your kiln so you can get a feel for the hot and cold spots. This is more important in larger kilns. Cones also provide a guide as to the accuracy of your thermocouple. 
6. Every kiln is different, and it may take some time to learn the idiosyncrasies of your kiln!
7. Orton have a treasure trove of resources and videos available to help you learn about cones and how best to use them.

Our created a quick reference guide may be helpful.

CONE DRIVEN ELECTRIC WHEEL

1.      WHISPER QUIET, POWERFUL 0,37kW MOTOR.

2.      TRIED AND TESTED SMOOTH CONE DRIVE

3.      COMFORTABLE SEAT

4.      EASILY CLEANED FIBREGLASS BASIN WITH DRAIN AND PLUG

5.      ALUMINIUM WHEEL HEAD

6.      AUTOMATIC "SWITCH OFF" ON PEDAL RELEASE

7.      SIMPLE AND INEXPENSIVE TO SERVICE.

ELECTRONIC BELT DRIVEN WHEEL

1.      WHISPER QUIET, POWERFUL 0,37 kW, THREE PHASE MOTOR DRIVEN THROUGH A SINGLE PHASE ELECTRONIC CONVERTER.

2.      HIGH TORQUE THROUGH THE ENTIRE SPEED RANGE.

3.      FLEXIBLE RIGHT HAND, LEFT HAND OPTIONS.

4.      FULLY MOBILE FOOT PEDAL

5.      CAPABILITY OF CONSTANT SPEED AND IDEAL FOR DECORATING AND TRIMMING.

6.      VERY FEW WEAR COMPONENTS RESULTING IN SIMPLE AND INEXPENSIVE SERVICING.

7.      COMFORTABLE SEAT

8.     EASILY CLEANED FIBREGLASS BASIN WITH DRAIN AND PLUG ALUMINIUM WHEEL HEAD

The firing temperature of casting slip varies depending on the clay used in the slip casting process.

Earthenware Slip – 1000ºC to 1120ºC is best, but we have taken it up to 1200ºC, where it goes slightly grey and it tends to warp. 

Stoneware Slip - 1000ºC for bisque and 1200ºC for glaze firing. It can be taken higher (up to1260ºC), however at this temperature it can warp (depending on the shape of the ware) because it becomes soft at temperature. An open shape is more likely to warp than closed shapes. 

Porcelain Slip - has many of the same properties of stoneware casting slips and therefore will react similarly at 1200ºC and 1260ºC, only it remains whiter. 

Charcoal Slip - is best fired to 1140ºC if no glaze is applied for the “blackness”. But if glazed, then it is best fired to 1120ºC only. This low temperature is because of the amount of flux in the body, and if it is taken higher it will bloat and ultimately melt into a puddle on your shelf!

Yes!  And it doesn’t mean your clay is bad, poorly quality or ruined.

Clay is an organic material and not sterile, therefore green & black mould can grow in any sort of clay, new, old, or recycled. 

If the conditions are right, mould will grow (moisture, oxygen, organic material, warmth & time). It is a sign of healthy bacterial activity that breaks down the organic matter in the clay.

A small amount of mould is perfectly normal, and many potters like the way it gives the clay more plasticity, making it smoother and more stretchable. 

However, excessive mould can smell bad and be unpleasant to handle.

Buckets, plastic bags, containers, and damp boxes can all create an environment where mould can grow.

If your concerned, the following products can be applied externally or even wedged in, to remove or help prevent excessive mould build up:

• Vinegar
• Bleach
• Hydrogen peroxide

Mould will burn off in the kiln, so your clays colour will not be changed by any mould, even the pristine white of porcelains is retained. 

If you have allergies or sensitivities, then you should use PPE (including gloves, mask and face shield) until you have disposed of, treated, removed or wedged it into the clay fully.

Generally speaking, yes.

Clays and glazes should be compatible in terms of their firing ranges. When selecting materials, you’ll often see terms like ‘Stoneware’, ‘Mid-fire’, or ‘Earthenware’ displayed on the packaging of both clays and glazes. Sometimes, these products will also list a firing range, such as ‘Mid-fire to Stoneware’, or a specific temperature or Cone range. These labels indicate the heatwork (the combination of temperature and time) necessary to transform clay into ceramics and glaze into its final hardened, glass-like coating.

Understanding Firing Ranges:

The firing range is crucial because it determines when the clay vitrifies—turning from fragile, dried clay into durable ceramics—and when the glaze matures, forming a smooth, glassy surface. If the clay and glaze on a single piece do not share a similar firing range, or if you mix different clays or glazes with mismatched firing requirements, one component will inevitably be underfired or overfired.

What happens when firing ranges don't match:

• Overfired Clay: The ware may warp dramatically (think Salvador Dali’s melting clocks) or even melt completely, risking damage to the kiln shelf, walls, elements, and anything else it touches.
• Overfired Glaze: The glaze colours can burn out or liquefy, running off the piece onto kiln shelves and causing significant damage.
• Underfired Clay: The clay may not vitrify, remaining brittle and prone to breaking easily.
• Underfired Glaze: The glaze may look matt and opaque, with colours that do not fully develop. It will also fail to become waterproof.

How to prevent firing issues:

1. Always check and understand the firing ranges of both your clay and glaze before use.
2. Maintain a firing log to record the specific clays and glazes you use for each piece.
3. Test new combinations on small test tiles before applying them to larger works.
4. Exercise extra caution when mixing two different clays or glazes together.
5. Use setters or casters when testing new clay and glaze combinations.
6. Keep your fingers crossed and cede to the Kiln Gods!

There are a few reasons why your clay may be too hard, including exposure to the air, stored in a hot location or the clay is getting old.

How do I fix hard clay?

Rehydrate the Clay – Use damp towels or soak in water.

Slaking Method (for Very Hard Clay)

• Break the clay into small pieces.
• Submerge the pieces in water completely until they dissolve into a slurry.
• Spread the slurry on a plaster bat or fabric surface to let excess water evaporate.
• Once it reaches the desired consistency, wedge it to prepare it for use.

Use a pug mill - If you have access to a pug mill or clay mixer, you can reprocess the clay, adding water gradually until it softens. Otherwise, you will need to wedge the clay by hand and gradually add small amounts of water using a spray bottle for better control.

How do I prevent hard clay?

Store Properly - Keep your clay in an airtight bag and seal it well after use.
Add Moisture Regularly - Place a damp sponge or cloth inside the bag with your clay if you plan to store it long-term.
Rotate Stock - Use older clay first to ensure it doesn’t dry out over time.

There are a few reasons why your clay may be too soft, including:

Excess Water Added - Overhydration during reclaiming or storage can make clay overly soft.
Improper Storage - Storing clay in a very damp or humid environment can increase its water content if not properly sealed from the atmosphere.

Improper Handling - When handling a bag of clay, care should be taken not to drop or bang the bag against hard surfaces, as this can cause the clay particles to become excessively mobile and thus create a product which is too soft to work with.
Clay Composition - Some clays naturally have a softer, stickier texture depending on their formulation, for example those containing a high proportion of ball clay.
Temperature Effects - During storage, large changes in the temperature can cause the clay to sweat inside the plastic bag, creating a film of water on the surface of the clay which creates a wet sticky product.

How do I fix soft clay?

Dry the Clay Out

• Spread the Clay on a Surface - Place the clay on a plaster bat, wooden board, or any absorbent surface to draw out excess moisture. Flip the clay occasionally for even drying.
• Use a Fabric Surface - Wrap the clay in a cotton or canvas cloth and let it sit to wick away moisture.
• Avoid Over-Drying - Check the clay periodically to prevent it from getting too hard.

Wedge the Clay - Thoroughly wedge the clay to distribute any remaining moisture evenly. This can help improve the workability of slightly soft clay.

Blend with Firmer Clay - Combine the soft clay with harder clay of the same type. Wedge or use a clay mixer to create a consistent texture.

How do I prevent soft clay?

Store in Airtight Containers - Prevent clay from absorbing excess moisture during storage.

Control Humidity - Keep clay in a cool, dry area to avoid additional moisture absorption.

Avoid Adding Too Much Water During Reclaiming - Use just enough water to soften the clay without making it sticky.

Don’t throw the clay around - Unless intentionally wedging the clay, handle the bag with care as force applied directly to the bag will soften the contents and may make the clay unusable at least for a while.

Yes, but…

People mix clays for a variety of reasons:

To Modify Properties - Combine clays to adjust texture, plasticity, colour, or firing temperature.

To Use Up Scraps - Reclaim leftover clays by combining them, as long as they're compatible.

Create Unique Effects - Layer or swirl different clays for decorative techniques.

Important Considerations:

Firing Temperature (Maturity) - Ensure the clays have similar firing ranges. Mixing a low-fire clay (e.g., earthenware) with a high-fire clay (e.g., stoneware) can cause issues like warping or unusual melting behaviour.

Shrinkage Rates - Clays with different shrinkage rates during drying and firing can lead to cracks or separation. Test a small batch first if you’re unsure of the shrinkage compatibility.

Plasticity - Some clays have more plasticity than others. Mixing a very plastic clay with a less plastic one can seriously diminish workability. Wedging thoroughly helps blend the properties evenly. 

Mineral Content - Clays with different mineral compositions may react differently in the kiln, affecting colour, glaze adhesion, or even causing unexpected results such as sudden rapid melting during firing due to a phenomenon known as a eutectic.  A eutectic can be created where the ratio of some ingredients combine to shorten the firing range of a clay by 50°C or more.   

Consistency - Mix clays of similar moisture levels to avoid difficulty during wedging. If one is much wetter, let it dry out slightly or rehydrate the drier one before mixing.

How do I Mix Clays?

Prepare Both Clays - Ensure both clays are at similar moisture levels.
Cut and Layer - Slice each clay into thin slabs and layer them together.
Wedge Thoroughly - Wedge the clays together until the mixture is uniform.
Test Fire - Make a small test piece and fire it to your usual temperature to ensure compatibility. Then repeat the firing at 10 - 20 degrees above your normal temperature. This will determine if you have sufficient firing latitude for unexpected melting behaviour.

Any Tips for Success?

Start Small - Test a small batch before committing to a large amount.
Document Ratios - If the result is successful, note the proportions for future use.
Be Creative - Use intentional mixing techniques (e.g., marbling or blending colours) to create visually interesting results.

Exploring ceramics reveals a range of clay types, each with unique qualities. 

Stoneware clay and Earthenware clay are prominent options, each with specific compositions and applications.

Stoneware Clay is renowned for its endurance and adaptability, occupying a revered spot in the ceramics industry. Maturing at approximately 1260°c to 1300°C it is a very durable and non-porous clay. However, given the impact of this high temp on electric kilns and element life-span, many people are moving to modern Mid-Fire Clays that can achieve the same results at a lower temperature.

Mid-fire Clay is similar to Stoneware but is popular because it matures at a lower temperature, approximately 1200°c to 1240°C.

Earthenware Clay embodies a more primal essence and malleable nature and offers a lower firing temperature. Maturing at approximately 1060°C to 1100°C it can be quite porous, so normally can’t be used in a dishwasher or microwave. Handy for plant pots as it slowly wicks moisture. 

Terracotta is a form of earthenware.

Porcelain is a super fine clay that matures at approximately 1220°C to 1300°C.  Generally considered harder to throw with and more costly to fire due to the heat requirements.

Cracking is a common issue in ceramics that can occur at various stages of the process. Understanding the causes and how to prevent them will help you produce stronger, more durable pieces.

Uneven Drying

Cause: Clay dries unevenly when some areas lose moisture faster than others, creating stress and cracks.
Fix: Dry your pieces slowly and evenly, especially larger or thicker ones. Cover with plastic and let the moisture equalise gradually. Turn pieces periodically to allow even airflow.

Poor Design

Cause: Sharp corners, inconsistent wall thickness, or weak joins can create stress points.
Fix: Ensure walls and bases have consistent thickness. Round sharp edges and avoid abrupt transitions in the design. Properly join pieces by scoring, slipping, and compressing well.

Inadequate Wedging

Cause: Air bubbles trapped in poorly wedged clay can expand during drying or firing, leading to cracks.
Fix: Wedge clay thoroughly to remove air pockets and create a uniform consistency.

Rapid Temperature Changes

Cause: Sudden changes in temperature during firing or cooling can cause thermal shock, leading to cracking.
Fix: Use a slow and controlled firing schedule, particularly during critical stages like bisque firing and cooling. Allow the kiln to cool completely before removing pieces.

Overly Wet or Dry Clay During Assembly

Cause: Joining pieces at different moisture levels can lead to cracking as the clay shrinks unevenly.
Fix: Assemble pieces at similar moisture levels (leather-hard is ideal). Score and slip properly to ensure a strong bond.

Incompatible Clay Body

Cause: Some clay bodies are more prone to cracking due to their composition or firing requirements.

Fix: Choose a clay body suitable for your project (e.g., grogged clay for large or sculptural pieces). Test new clay bodies before using them for significant projects.

Excessive Drying Shrinkage

Cause: Clay with a high shrinkage rate may crack as it dries and shrinks unevenly.
Fix: Use a clay body with lower shrinkage if cracking is a persistent issue. Dry pieces slowly and evenly to reduce stress.

Overfiring

Cause: Firing at too high a temperature can weaken the clay and cause cracking.
Fix: Verify the correct firing temperature for your clay and glaze. Use cones to ensure accurate firing in your kiln.

Improper Handling After Firing

Cause: Mishandling finished ceramics, especially large or thin pieces, can create cracks.
Fix: Allow pieces to cool completely in the kiln before handling. Support delicate or large pieces properly when moving them.

Cracks in Glaze

Cause: Crazing or cracking in the glaze can result from an incompatible glaze and clay body.
Fix:Test glaze fit with your clay body to ensure proper thermal expansion compatibility.

By identifying when and where the cracking occurs (during drying, firing, or post-firing), you can pinpoint the cause and take appropriate steps to prevent it. Testing and adjusting your process can lead to stronger, more reliable ceramic creations.

Glaze blistering, also known as "bubbling," occurs when trapped gases in the glaze or the clay body expand during firing, creating bubbles that burst and leave crater-like marks.

Here are common reasons for blistering and how to fix them:

Insufficient Firing Time or Temperature

• Cause: Gases from the clay or glaze don't have enough time to escape before the glaze cools and solidifies.
• Fix: Extend the firing time or increase the hold at peak temperature to allow more time for the glaze to mature and gases to escape.

Poor Glaze Application

• Cause: Glaze applied too thickly traps more moisture and air, leading to bubbling during firing.
• Fix: Apply thinner, even layers of glaze. dip, brush, or spray evenly, and let each layer dry thoroughly before applying the next.

Contamination

• Cause: Dust, dirt, or oils on the bisqueware can interfere with the glaze, creating bubbles.
• Fix: Wipe your bisqueware with a damp sponge before glazing to remove any surface contaminants.

Bisque Firing Issues

• Cause: If the bisque firing is too low or rushed, organic materials and moisture remain in the clay, releasing gases during the glaze firing.
• Fix: Bisque fire to a higher temperature (e.g., cone 04 instead of cone 06) to burn out impurities more thoroughly.

Clay Body Issues

• Cause: Some clay bodies contain organic materials, grog, or impurities that release gases during firing.
• Fix: Test your clay for compatibility with the glaze and consider switching to a less gas-prone clay body if issues persist.

Incompatible Glaze Formula

• Cause: Certain glaze recipes are more prone to bubbling due to ingredients that release gases at high temperatures (e.g., carbonates or organic materials).
• Fix: Adjust the glaze recipe to reduce volatile ingredients, or reformulate with a flux that melts at a lower temperature.

Rapid Cooling

• Cause: Cooling the kiln too quickly can cause bubbles to solidify before they pop and smooth out.
• Fix: Slow down the cooling cycle, especially in the early stages after peak temperature.

Firing Schedule

• Cause: Firing too fast or not allowing proper soaking at certain temperature ranges can trap gases.
• Fix: Use a controlled firing schedule, with slower ramps and soaks, particularly between 500°C–900°C (932°F–1652°F) to burn out carbonates and organics.

Re-glazing and Refiring

• Solution: If the bubbling is minor, you can sand the surface, clean it, and apply a thin layer of glaze before refiring. Ensure the firing schedule is adjusted to address the original issue.

By identifying the specific cause of the bubbling, you can take targeted steps to resolve it. If you’re unsure, test changes on small pieces before applying them to a full batch.

Mixing the glaze from powder for dipping, pouring, or spraying: 

1. Wear a suitable protective mask.
2. Sprinkle the glaze powder into a suitable container of water. 
3. We suggest you start with a 1:1 ratio, (i.e. 1 kg of powder to 1 litre of water).
4. Stir thoroughly.
5. Leave to settle overnight and skim off any surplus water. 
6. Stir again and then sieve through an 80 mesh (or finer) sieve.
7. If necessary, add small amounts of water to achieve your desired consistency.
8. We suggest a consistency a bit thicker than Full Cream Milk (like pouring cream) for a dipping glaze, however you may want it thinner for spraying or thicker for pouring. 
9. Your glazes may start to settle during use, you should regularly stir or agitate during your dipping / pouring / spraying session. 

Note: When adding water: add small amounts cautiously and stir well between each addition until you reach your desired consistency.

The more water you have in a glaze, the less solid particles there are (proportionately) to stick to the bisque! Less solid particles means a thinner glaze application. Each glaze (and each potter) will have a different “ideal” ratio of solid particles to water. 

Liquid glazes can settle out over time. They sometimes set hard at the bottom of the container, making them difficult to re-mix. To overcome this a flocculent or anti-set solution should be added a little at a time. 

Epsom salts are a good flocculating agent. Adding 1% saturated Epsom Salt solution to your glaze mix with thorough stirring will re-suspend your glaze mix. 

Some common glaze problems (or perhaps the effect your looking for) and their solutions as excerpted from Robin Hopper’s book called 'The Ceramic Spectrum'.

Cloudy or milky transparent glazes often occur due to micro-bubbles, crystals, or other factors that affect transparency. Commonly caused by the glaze being applied to thick, however firing temperature, glaze chemistry, & interactions with the clay body can also be the cause. Solutions for Clear Glazes include: 

• Apply glaze in thin, even layers. 
• Ensure the glaze is fired at the correct temperature for it to fully melt. Refiring it can sometimes help.
• Ensure the glazes are proper stirred (not shaken). 
• Consider the glaze chemistry and how it interacts with your clay body. 
• Test different glaze applications and firing temperatures on test tiles to find the right balance. 

Crazing is the most common glaze defect, and normally the easiest to correct. In both crazing and shivering the eradication of problems relies on matching the thermal expansion characteristics of both body and glaze. Common factors that increase the risk of crazing include:

• Sudden temperature and humidity changes.
• Moisture getting into the glaze.
• Wares being bumped or knocked repeatedly.
• The kiln heating or cooling too quickly, where the glaze will shrink quicker than the body of the ware.
• The wrong clay body for the glaze. High silica content will cause crazing.

Shivering is the most problematic of glaze defects, particularly in any functional ware, since slivers of glaze from the edges can drop into food or drink. These slivers are usually small, sharp, jagged-edged pieces that detach themselves from the body. It tends to happen because the thermal expansion of the body is more than the glaze's.

• The best way to resolve this is to try another clay body of the same fired colour and temperature range, to get a better ‘glaze fit’.

Crawling is caused by a high index of surface tension in the melting glaze. It is triggered by adhesion problems, often caused by bad application. It occurs where a glaze does not fully adhere to the surface of the clay. Crawling is more common in matte glazes than in fluid ones. Crawling can also occur when one glaze is applied over another, particularly if the first is allowed to dry out completely before the second application. 

• Follow this link to read a comprehensive article about crawling.
• The best way to correct crazing is to change to a different clay body, which better fits the glaze or try increasing the firing temperature.

Pitting and Pinholing are the most annoying and difficult glaze defects to cure. They can be caused by a badly controlled firing cycle, the glaze composition, or can originate with the body, particularly highly grogged clay bodies. The following remedies should be tried to cure pinholing or pitting:

1. Apply the glaze less thickly
2. Make the glaze more fluid to alter its surface tension.
3. Lengthen the firing cycle to give the gases longer to escape.
4. Increase the maturing temperature of the glaze.
5. Hold the kiln at the glaze maturing temperature for a longer soaking period.
6. Cool the kiln down more slowly.

Blistering and blebs are caused by the escape of gases from the clay body or the glaze, usually the result of either an excessively thick application of glaze or incomplete clay preparation (wedging, blunging, etc). Therefore the solution is prevention:

• Make sure the clay is well prepared.
• Has the ware adequately matured and lost most of the escaping gases in the bisque firing.
• Increase the ventilation of the kiln and its environments.
• Make the glaze more liquid or apply less thickly.
• Review your clay and glaze choices.

The Brush-on glaze contains a medium so that it can be stored in a liquid form and allows it to be applied smoothly with a brush (whereas the powders don't). Its good practice to stir the glaze until you notice it becoming nice and creamy. Shaking the glaze vigorously changes how the glaze chemicals react, so it's not recommended.

The Powder glazes are designed for dipping, spraying or pouring. You have more flexibility in regards to the volume and consistency to achieve your desired results. However, you may not get an even application if brushed on.

YES!

Some people fire a single piece 3, 4 or even more times until they get exactly what they like. 

Re-glazing is also useful in repairing small chips or cracks in the pottery along with fixing a glaze problem. Layering new glazes on old glazes can also can add an interesting texture & depth.

The only rule in multiple firings is that you can't re-fire at a hotter temperature than a previous firing, or you will burn off the lower temperature glaze.

Most of our other glazes are food safe when used as instructed and fired to maturity on an appropriate clay body. However, some metallic and low fire glazes are NOT food safe... you should always check the container / package.

Generally speaking, food safe implies that the ware is:

• Non-porous (so liquids and bacteria can’t seep in)
• Fully sealed with a food-safe glaze on all surfaces that touch food or drink
• Fired to maturity (so the clay and glaze mature together)

Its always wise to refer to the Safety Data Sheet of a product if you are concerned.

Some people recommend the 'Lemon Test' - squeeze on some lemon juice, and leave the lemon wedge on the piece of ware overnight. If there is no colour change then leaching hasn't occurred and your pieces are likely suitable for functional use.

For lots of helpful FAQ's about the Claybright range of underglazes and their other products:

Check out the dedicated  Claybright FAQ page.

°Cadmium glazes are notorious for being temperature sensitive.  This means that when firing a cad glaze be it yellow, green, orange or red, care should be taken in the firing.

Cad glaze will appear transparent if over-fired or to thinly applied.  If you have access to a brush on cad glaze, more glaze can be applied to the surface where it burnt out and re-fired to the glaze temperature (1060°C).  Just remember that cad glazes should be applied very thickly.  When firing these glazes do not soak them at temperature.  FIrst thing to do is make sure that your kiln is not packed too tightly.  Cad glazes must "breathe".  Then start your firing by going to 100°C and holding it there for an hour or two to warm up the ware in the kiln.  Thereafter go up to 1060°C at a rate of 250°C an hour.  If your firing consists of bigger platters and sculptures keep on firing slowly to 600°C ( a rate of 150°C per hour) and only then go to a rate of 250°C per hour to 1060°C.

If you are firing manually (with cones), put the kiln on setting 1 for 2 hours then on 2 for 2 hours then on 4 for 1 hour and then on 6 until the cone bends.

Carmen red glaze is not the only red cad glaze in our range, we also have some Gare glazes that are cadmium based like the Xmas Red and Fire Engine Red.  These should not be fired higher than a 1000°C.  In application they state paint first coat wait 2 hours then paint the second coat wait a further 4 hours and then paint 3rd coard wait 8 hours and then pain the 4th coat.  The finished thickness should be between 1,5 and 2 mm thick.  When firing it - same as for Carmen red but it only fires to 1000°C with no soak.

Paper stencils, adhesive backed stencils, stickers, masking tape, contact paper, stencil paper (acetate), paper doilies, lace – all work as stencils.

Most items used as stencils will disappear after firing as they burn off in the extreme temperatures.

Li2O.Al2O3.4SiO2.

We no longer stock Spodumene, a  good source of Lithium, a flux at stoneware temperatures.

Spodumene is used in white bodies and glazes and lowers the vitrification point.

You could try substituting 4 g of Silica and 1 g of Alumina for every 1 g of Lithium Carbonate instead.

Both of these products have been discontinued some years back and are no longer available.  Potters worldwide have been reformulating their glazes as a result.  More information can be found at www.digitalfire.com/gerstleyborate/substitutes.html

We were recently asked what the difference was between kaolin and talc, good question. But before getting to the differences, let's first see what they have in common.

They are both fine white powders that come from digging a mineral out of the ground and refining it. If you take a microscope and look at the particles close-up, they both look like tiny flat plates, which are called (surprise, surprise), platelets. This platelet shape makes them good at cutting out the light, which is why we put them into paints and ceramic glazes to help with opacity.

Kaolin and talc have a lot more in common: They are both inert, which means they take no part in chemical reactions. They are also both insoluble in water, so they do not dissolve (although it looks like they do when all the particles are dispersed and form a milky solution).

Although both are minerals, only kaolin is called a clay. In fact kaolin's common name is china clay. The common name for talc is talcum powder and it is the softest mineral on earth. That must be why it is chosen for use on babies bottoms!

Kaolin is also a soft mineral, though. It comes just above talc on the Mohs hardness scale of minerals:

Looking at a pile of kaolin powder and a pile of talc powder, however, you will notice an obvious difference. The talc is much whiter (unless it is very impure). If you put your hand into the powder, you will find that although the kaolin makes your hand white and dusty, the talc sticks to it like blazes. And to your clothes, your face, the dog, etc.

That's the biggest difference, I think. Talc is hydrophobic which means water-hating. Hence it loves anything organic like you, your face, the dog.....you get my drift.

Kaolin on the other hand, loves water so it is hydrophilic. That makes it much easier to disperse into water than talc, which tends to sit on top of it. Talc may be water-hating but surprisingly, you can still disperse it into your water-based paint without too much of a problem. This water-hating property does come in useful in waterproofing products, where you need ingredients that help to reject water.

Open a chemistry book (does anyone still do that these days?), OK strike that, go to Wikipedia, and it will tell you that kaolin is a clay mineral and falls into a family called alumino-silicates. Talc, however is a magnesium silicate. This would explain their different behaviour. However sometimes when you are just using them as inert fillers, their differences are not important and you would just buy whichever is cheapest - usually kaolin. Like when you are using them in laundry soap bars, for example. For white toilet soap, though, you will need whiteness, so then you would chose talc rather than kaolin.

It gets even more interesting when you melt these two minerals, as happens when they are used in ceramics. Kaolin is a basic ingredient of most ceramic bodies and glazes and is needed for its alumina content, while talc is used mainly as an additive which helps to control thermal expansion, reduce crazing and improve the whiteness of the ceramic article or glaze.

Just like a brother and sister, these two minerals sometimes work well together and sometimes they compete with each other. But we love them both, just the same (OK, I admit it, I prefer kaolin, but that is only because it has been my baby for so long...)

THIS ARTICLE WITH THE KIND PERMISSION OF JENNY JAY OF SERINA TRADING : www.kaolin.co.za

Kaolin and calcium carbonate are both used as fillers or extenders, in other words they make something cheaper. By adding them the volume goes up and the cost per ton goes down. What music to our ears!

But add too much filler and you start to lose good properties, so it is always a trade-off of cost versus quality.

Fillers replace a bit of something that is much more expensive, such as titanium dioxide in paint, soap in soap bars, resin in plastic parts, pulp in paper or rubber in conveyor belts. Like it or not, there is a filler in nearly everything we see around us.

If kaolin is called china clay and the mineral is kaolinite, then calcium carbonate is called limestone, calcite or chalk, and the mineral is calcite. Limestone is the name of the sedimentary rock it comes from. However you also get calcium carbonate from marble, chalk and crushed sea shells.

The main difference in my mind between kaolin and calcium carbonate is that kaolin is a clay, while calcium carbonate is a salt. That means it can dissolve. Lucky for us, it won’t dissolve at high pH such as in paint or soap, or in organic media like plastics or rubber. It only really dissolves in acids.

You can be pretty sure that kaolin, though, will not dissolve whatever you do to it. (The only thing I know that can dissolve kaolin is a super-strong acid called hydrogen fluoride).

For many years, printing paper was made in acid conditions. This meant calcium carbonate could not be used as filler because it would dissolve. Now most paper mills have gone over to alkaline sizing. Thus calcium carbonate now beats kaolin as the main filler for paper.

Calcium carbonate is preferred for paper because it is much whiter than kaolin. Its ISO-Brightness is usually 96%, compared to around 83% for a typical kaolin. Quite a big difference!

Another big difference with these two fillers is the shape of their particles. Kaolin has plate-like particles (platelets) while calcium carbonate particles are irregular rhombohedral (or effectively round) in shape. This is why kaolin particles cut out the light better than calcium carbonate particles. In the paint industry we say kaolin has better hiding power than calcium carbonate.

Some clever scientists have now been able to make precipitated calcium carbonate with a platy shape for the paper industry (for more about this, click here).

I recently visited a lime factory and saw the age-old process of making lime from calcium carbonate. Not surprisingly, you are sure to find a lime factory next to a limestone deposit. The limestone is crushed and calcined to 930 degrees C to form what is called burnt lime/quicklime or unslaked lime:

CaCO3 + heat = CaO + CO2

The burnt lime or calcium oxide is reactive to water (it heats up and gives off steam). This process is called slaking and the result is slaked lime or calcium hydroxide – Ca(OH)2. That’s the stuff that is sold as builder’s lime. It is also used in water treatment and chemical plants for pH control.

Calcium carbonate is useful to us humans as a source of calcium and as an antacid. It is also used as the carrier in many forms of tablets and pills. Kaolin’s main medicinal use is in diarrhoea remedies.

So these two useful fillers are not only all around us, they may also be inside us!

This article with kind permission of Jenny Jay - Ph.D (Chemistry) ATSC - SERINA TRADING www.kaolin.co.za

The best way to do this is to peel back the top canvas sheet and to place a wooden board or batt on top of your clay slab, then turn the boards over and your clay slab will now be on top of the wooden board or batt.   

Remove the drive board, your clay slab is ready for cutting.

Slabbing can be very tricky at times.  Here are a few tips to make the process a little easier.

1.  When scoring/ cross hatching the edges it needs to be relatively deep.  The clay slip applied to the area, scored again until it is mush.  The idea is that when the two pieces are pressed together the scored edges will mix.

2.  Take a tool and run it along in the corner, creating a shallow groove.  This action will help compress the clay in the joint.  Next is roll a thin coil of clay.  Whilst supporting the joint on the outside, reinforce the joint by smearing the coil into the groove.

3.  When it comes to drying your pieces, it is always advisable to dry it out slowly.  Keep it completely covered for the first 24 hours.  Thereafter keep it partly covered for +/- 3 - 7 days, only then open it up to dry naturally.

When rolling out a slab it is always advisable to roll in a cross hatch fashion, otherwise the clay particles align in one direction.  This causes the clay to shrink differentially creating stress on the joint.

1. To mix plaster of paris you need a ratio of 1.2kg of plaster of paris to 1litre of water (or 1kg plaster of paris to 833ml water).

2. Pour water into a bucket, sieve plaster of paris quickly through your fingers into the water, to disperse powder evenly over the surface of the water.

3. When the plaster of paris forms a peak in the water let it stand for approximately half a minute (to allow the plaster of paris to absorb the water).

4. Stir mixture vigorously with your hand until all the lumps have dissolved.

5. Let mixture stand for a few seconds until it becomes a creamy liquid.

6. The plaster is now ready to pour into the mould.