Resources

1. Why do black specks appear in my glaze?
   

   Black specks are usually caused by contamination from dirt. This can come from a dirty brush, bisque, glaze container, or kiln. To prevent this, ensure all tools and surfaces are kept clean.

    

2. What causes glaze to blister or bubble?
   

   Blisters and bubbles result from trapped gases released from underfired bisque or glaze. To fix this, sand down the blisters, apply a thin coat of glaze, and re-fire at a slightly higher temperature. Soaking the piece for 30 minutes at the end of re-firing may help.

    

3. Why does the colour peel off after firing?
   

   Peeling usually happens due to heavy glaze/underglaze application, dirty bisque, oil or grease contamination, or rapid cooling. To prevent this, apply glaze with clean hands, ensure bisque is clean, use thinner coats, and avoid forced cooling.

    

4. What causes cracks in fired ceramics?
   

   Cracks can occur due to uneven or rapid heating or cooling. If the edges of the cracks are sharp, they happened during cooling; if they are smooth, they occurred during heating. To prevent this, fire more slowly and avoid forced cooling. Cracks can also result from glaze-clay incompatibility.

    

5. How can I fix craters in my glaze?
   

   Craters are usually due to under-firing. Apply additional glaze to the affected areas and re-fire at a temperature 10°C higher than the first firing, with a 10-minute soak.

    

6. What is crazing, and how do I fix it?
   

   Crazing appears as a fine network of cracks on the glaze surface, caused by underfired bisque, glaze-clay thermal expansion mismatch, or rapid cooling. To fix it, re-fire at a slightly higher temperature.

    

7. Why do my decals fade after firing?
   

   Fading results from incorrect firing temperatures. Check the manufacturer’s recommendations. If underfired, re-fire to the correct temperature. Overfired decals cannot be salvaged.

    

8. What causes glaze to creep (bare spots in the glaze)?
   

   Creeping occurs due to dust, grease, or oil on the bisque, under-firing, or firing before the glaze dries. To fix this, apply more glaze to the bare spots and re-fire.

    

9. How do I fix problems with lustres?
   

   Lustres can flake or peel if applied too thickly and will frost if overfired. To fix overfired lustre, fire to 1000°C to burn it off, then reapply and re-fire.

    

10. Why does metallic glaze look dull or crack?
    

    Metallic glazes appear dull if applied too sparingly or underfired. Over-firing or excessive glaze application causes cracking. Underfired metallics can be re-fired to the correct temperature, but overfired metallics must be burnt off at 1000°C and reapplied.

     

11. What causes pinholes and pitting in glaze?
    

    Pinholes occur when volatile materials are released during firing, causing bubbles to freeze in the glaze. This can result from rapid heating or cooling, dust, dirt, overfired glaze, or underfired bisque. To fix this, re-fire at 30°C higher than the original firing temperature.

     

12. Why does my red glaze have gray or black spots?
    

    Gray areas indicate excessive glaze application. Black spots result from over-firing, contamination from yellow or green glazes, or inadequate kiln ventilation. To fix this, reapply the glaze, allow more spacing between pieces in the kiln, and re-fire.

     

13. How can I correct rough matte and satin glazes?
    

    These textures result from under-firing, uneven glaze application, or insufficient glaze. Reapply glaze and re-fire.

     

14. What causes smooth textured glazes?
    

    Smooth glazes may result from insufficient glaze application or over-firing. This can be corrected by adding more glaze and re-firing.

     

15. Why does my glaze have streaks?
    

    Streaks can be caused by thin or uneven glaze application, improper stirring, or misaligned glaze coats. To fix this, re-glaze the piece and re-fire.

Key information

To calculate the cost of running your kiln you will need to know the following information:

• How much electricity your kiln consumes in an hour. This is expressed in Kw. Most good manufacturers will state on the kiln (normally on an information plate on the kiln) the Kw used per hour – e.g. 10Kw
• You then need to know the cost per Kw. You should find this on your utility bill. This can be anything from R1.30 to R2.50 depending on your electricity supplier.
• Finally, you need to know how long your programme (or firing cycle) will be.

Firing programme example

This example is based on a 5.2 cu ft. front loading kiln:

• Electricity consumption per hour: 6.7Kw
• Cost per Kw: R2.50
• Total running time: 6 hours
  • • 1st ramp up to 500°C @ 250°C/hour = 2 hours
    • 1st soak for 1 hour = 1 hour
    • 2nd ramp up to 800°C @ 300°C/hour = 1 hour
    • 2nd soak for 2 hours = 2 hours

Cost Calculation:

• Consumption X Cost per Kw X Amount of hours
• 6.7Kw X R2.50/Kw X 6 hours) = R100.50

It will thus cost you R100.50 to run your kiln for a six hour cycle.

Please note this example is based on costs in South Africa in ZAR (Rands)

Our selection of kilns have grown steadily over the last few years.

With so many available options, making a decision could be somewhat overwhelming. To help you sort through the confusion use these steps to guide you towards selecting the kiln that best suits your needs. If you have more questions, our dedicated team is only a click, email, or phone call away.

Step 1: Electric or Gas?

Electric kilns are easier to manage and tends to be safer. With the exception of large Industrial kilns that use ‘piped’ Sasol gas, small installations using bottled gas tends to have a higher running cost than its electric equivalent.

Traditionally gas has always been used for ‘reduction firing’, Raku work, and for temperatures higher than 1400°C.

Step 2: Electricity Requirements

People often overlook the power that is available to run a kiln. There are two main types available in South Africa: Single Phase or Three Phase.

Most residential homes only have 60 amps, single phase electricity supply. When selecting a kiln, check the specifications to see if it needs single or three phase power. This does limit your choices as very few kilns are able to run from a normal household plug. We do not recommend installing kilns larger than 7 cubic feet (cu ft).

In most cases a small amount of work will be needed to meet the legal requirements for an electrical installation. A qualified electrician will need to add a suitable breaker, appropriate wiring, an isolator switch and possibly an additional breaker on you main distribution box. This is not an expensive exercise but vitally important to ensure your electric connection is safe and up to code.

There is no significant cost difference between using single or three phase electricity, it comes down to what type you have available. You can apply to have Three Phase electricity installed at your premises if this is the route you wish to take.

Step 3: Type of kiln

Before selecting a kiln consider the type of work you want to use the kiln for, the size of the items you plan to produce, the quantities you would like to make with each firing, and how often you intend to fire. Kilns come in different sizes, so make sure the heat chamber is large enough for the items you are planning to produce.

The most commonly used kilns are front and top loaders with both having pro’s and con’s. Let’s have a look at some of the kilns available.

Front Loading

These kilns are easier to pack and unpack. They are fitted with a front opening door and most are made with a stand. Smaller options without a stand can be placed on a table top or bench. Front loading kilns are sturdy and heavy, making them hard to move.

Top Loading

Conventional top loaders tend to be smaller, taking up less space, and have a round or oval fire chamber. They are ideal for small work areas and can be fitted with wheels, making them easier to move around.

They tend to be less expensive and the smaller ones will work on a standard household, single phase socket. Beginners often prefer to start with a top loading kiln as it requires a smaller initial investment.

They are harder to load. You need to load them from above and need to layer the shelves as you pack the kiln. They are also lower and you would need to bend over to pack them, taking its toll on your back.

Top loaders are not built with a sturdy metal frame and depend on the internal insulating bricks for their rigidity. It is more prone to damage if treated roughly.

Glass slumping & fusing

Traditional glass slumping and fusing kilns looks like a large square box with a top opening lid. Because of their shape they are often called ‘coffin kilns’. They tend
to be wide and shallow to allow space for flat sheets of glass that can be fused or slumped over a mould.

Glass needs radiant heat to soften and mould. Because most of the work starts out flat the majority of the heat is designed to come from above.

These kilns cannot be used to fire pottery as the maximum temperature they achieve are about 900°C. This is too low for ceramics.

Custom Kilns

There are many different types and shapes of kilns used for various applications and in many industries. The need for heat is widespread and varied and we can design and build a kiln to your specifications and heating requirements.

Step 4: Size

Select a kiln that will be capable of firing the largest item you will produce, consider how long it will take you to make enough pieces to fill your kiln, and decide how often you want to fire.

Do you think your current production will increase over time? Kiln owners will typically tell you to select a kiln with larger capacity than your current needs, because as you grow your hobby or business, you will outgrow your current kiln as well.

To determine which size best suits your needs, consider the following:

• What type of items/products do you plan to produce?
• If you make larger pieces, do you make them regularly or on the odd occasion? Can you fire your
  larger pieces off-site?
• What quantities do you wish to produce?
• For maximum efficiency you need to fire a fully loaded kiln. Think about the time it would take to
  make the items you need to fill your kiln.

A small kiln is great if you make dolls, jewellery, or smaller items. If you make larger items and quantities or
throw (which is considerably faster than hand-building), we recommend a kiln of at least 5 cu ft.

Step 5: Control Options

Manual kilns are obsolete and only die-hard enthusiast still prefer this method of firing. It requires constant attention and vigilance. You will need to be in the vicinity at all times to monitor the firing cycle. This requires time, that most of us do not have.

In you search for a kiln, you might encounter an Automatic kiln that is fitted with a kiln sitter. This is a mechanical system that uses a cone, placed in the kiln sitter. Once your kiln reaches the desired temperature, the cone folds over, and triggers the kiln sitter to switch the kiln off. Although effective, this mothed is dated. Your kiln can easily be converted to digital. Still need convincing? Read the benefits below.

Benefits of using a Digital Controller:

• It requires less of your time. You program the firing cycle, press start, and the digital controller does the rest.
• If the electricity should go off for some reason (load shedding), your controller will automatically start your kiln up again when the power is back, recalculate, and continue with the firing cycle.
• You will never need to use a cone again. The controller regulates and monitors the temperature of your kiln.
• You can program up to 36 firing cycles into your controller. One for every type of clay or glaze you might want to fire. Next time you need to fire some Porcelain, select the program and press start.

Programmable controllers are suitable for work in all mediums.

We will be launching a controller you can manage via Wi-Fi. Digital will soon go wireless. Most manual and mechanical kilns can be easily converted to digital.

Step 6: Kiln Furniture

You will need to consider the shelves and props you will need for your kiln. The type of kiln, size of your items and the way you will pack your kiln will determine how many shelves and props you will need to use your kiln’s capacity to achieve maximum efficiency.

Step 7: Making the ultimate decision

We hope this information will steer you towards choosing the kiln that will suit your needs and budget. We do try and keep the most commonly used kilns in stock, if however it needs to be manufactured it can take up to 4-6 weeks. Contact us for more information or a quotation.

This guide will assist you to install a kiln element. It should be noted that this is the way Van Tuyl fits elements on a Front Loading Kiln but this could change from time to time, so always check with your supplier. Fitting elements to other kilns (e.g. top loaders) can also be a DIY job, ask your manufacturer for details.

It is normally fairly easy to change the elements in your kiln.

Steps to follow

• Make sure your kiln is switched off and disconnected from all power sources.
• Before you start to disconnect any wiring, mark all the wiring and take photos that you can use to refer to later.
• Most elements are supplied as a closed coil with 2 tails on either side. Most kilns are built as a standard, however over time some changes might have been made, the tails should compensate for any changes that might have been made.
• Inside your kiln the element normally consists of several rows. Depending on the size of you kiln these rows could run back and forth across the side and back walls as well as the door. Do not make the mistake of thinking that each row is an element.
• Each element (normally) has a ‘Power IN’ and a ‘Power OUT’ where the tails of your coil fits through. You should find these on the back wall of your kiln.
•  Count the number of rows on the wall where you need to fit the element and divide the closed coil into equal lengths or segments.

IMPORTANT: Elements are manufactured to ensure the correct Amperage. Never cut or altered the element as this could affect the Amperage.

• You should now stretch the element to the same length as the groove in the kiln wall.
• Clamp the tail to (for instance) a workbench and stretch each segment to the required length. (In a standard 5.2 cu ft. Van Tuyl kiln it will be 440mm long.)
• Once you have created the stretched segments, you need to straighten out the segment elbow. This is the section between each segment. Do this by straightening out a coil or two with a pair of pliers. Each segment should now fit nicely into the horizontal grooves in the kiln wall.
• There should be a smaller vertical groove in the brick between each horizontal groove. This is where you need to fit the segment elbow you made between each segment.
• It is not an issue if the segment is not totally exact as long as the fit into the horizontal groove neatly and are not bunched together (you can always stretch the coil out a little bit more if need be).
• Now push the tails through the holes in the back wall where they can then be connected to the power on the back of the kiln.
• Sometimes elements are pinned to the bricks using element pins. If you do have some element pins you can do this, but it is not necessary. You can make small element pins from the old element wire. These pins are U-shaped and easy to make using pieces of wire about 50mm long and then bent into a U shape. Push the pins into the soft brick to secure the element.
• The element tails needs to be connected to the electrical power. You can do this either with a line tap or a bolt connection. If you will be using a Bolt connection create a loop at the end of the element tail for the bolt to go through and connect as shown in the illustration below.

All connections should be as tight as possible to prevent a ‘Hot Joint’ that can impact the performance of your kiln.

There is a common misperception that electric kilns for ceramics are expensive to operate. However, when compared to gas kilns and other factors, this is not necessarily the case. Below is a simple method to calculate the cost of running an electric kiln.

Key Information:

To determine the cost, you need answers to three key questions:

• What is the Kilowatts usage of your kiln?
  • The electricity consumption of your kiln is expressed in kilowatts per hour (kW/h). This information is typically
    found on an information plate on the kiln, e.g., 6.6 kW/h or the Amps the kiln uses.
  • If you have the total Amps of your elements, use the following calculation: 1 Amp = 0.22 kW/h. For example, if
    your kiln uses two 15 Amp elements (total 30 Amps), the calculation would be 30 x 0.22 = 6.6 kW/h.
  • If the above information is not available, a good kiln manufacturer can provide an estimate based on the
    internal dimensions of the kiln.
• What is the cost of electricity per kilowatt-hour (kW/h)?
  • You need to know the cost per kW/h, which can be found on your utility bill (e.g., Eskom, COJ). This cost
    typically ranges between R2.10 and R3.20 per kW/h, depending on the supplier.
• What is your firing time?
  • • Know the duration of your firing program. Most ceramic programs run between 8 and 10 hours. Note that the
      firing time is not the same as the time your elements are actually on and consuming electricity. A good
      estimate is that your elements are on for approximately 70% of the firing cycle time.

Cost Calculator

Use this simple calculation to work out the cost of a firing.

Consumption (kW/h) × Cost per kW (R) × Firing Cycle Time (hours) × 70%=Cost of Firing (R)

Examples:

1. For a 30 Amp kiln:
6.6kW × R2.30per kW/h × 8hours × 70% = R85.00
2. For a 40 Amp kiln:
8.8kW × R2.30per kW/h × 8hours × 70% = R141.68
3. For a 45 Amp kiln:
9.9kW × R2.30per kW/h × 10hours × 70% = R159.39

By understanding and applying these calculations, you can accurately estimate the cost of firing your electric kiln and see that it may be more affordable than you previously thought.

If you’re experiencing firing issues with your kiln, pinpointing the cause can be frustrating. Is it the glaze, the bisque, the application, or the kiln itself? While multiple variables can be at play, troubleshooting your kiln systematically can help you find a solution quickly and efficiently.

Step 1: Check Your Kiln’s Settings and Controller

Before assuming a kiln malfunction, start by reviewing your controller settings. Many firing issues stem from programming errors.

• Use the controller’s review feature to verify the last inputted program. Ensure it aligns with your intended firing schedule and the load inside the kiln.
• Common programming mistakes:
  • Unintended delay: If your kiln isn’t turning on, check if a delay has been set.
  • Slow ramp rates: If the temperature is rising very slowly, ensure the ramp rate isn’t set too low (e.g., 1°C per hour).
  • Incorrect target temperature order: If the second step (target temperature) is set lower than the first, the controller may reject the program.
  • Error and warning codes: Check the controller for any error messages, such as thermocouple failure, which can directly indicate the issue.

Step 2: Identify What Has Changed

If your kiln has been firing successfully and suddenly develops issues, ask yourself: What has changed? Some common changes that can affect kiln performance include:

• New suppliers: Different material compositions can impact firing results.
• Different user programming the kiln: An incorrect program entry or different packing technique can cause variations.
• Kiln relocation: If the kiln has been moved, improper reassembly may be affecting performance.
• Thermocouple placement: If it’s inserted incorrectly (e.g., touching the kiln wall), temperature readings may be inaccurate.
• Recent repairs: If the kiln has been serviced, confirm that it was reassembled correctly.
• Time of day for firing: Voltage fluctuations, particularly in summer months, may impact heating consistency.
• Glaze or clay body changes: Even slight formulation alterations can affect results.
• Loading adjustments: Uneven mass distribution in the kiln can cause uneven firing.

Step 3: Isolate the Issue

If you’ve ruled out programming and external factors, check the kiln’s essential functions:

• Is the contactor engaging? This switch activates the heating elements, and you should hear a distinct ‘click’ or ‘clunk.’ No sound may indicate a faulty contactor.
• Are the elements working?
  • Visual inspection: Look for visible damage, breaks, or disconnections.
  • Test fire the kiln empty: Run a short program (Ramp: 250°C per hour, Target: 250°C) and check if all elements glow evenly.
  • Potential issues:
    • One element not glowing at all → Likely a broken element.
    • Cool spots on certain rows → Worn-out elements.

Final Steps: Safety & Manufacturer Support

Before performing any maintenance, always switch off the kiln both at the unit and at the power source. Consult your kiln manual and the manufacturer’s website for guidance. If the problem persists, reach out to your kiln manufacturer with detailed observations to help expedite troubleshooting.

As kilns get older over time and after many firing, your bricks may start to get a little loose. Over time bricks do shrink slightly and may need to be pinned back into place, or it may be due to damage etc. Some manufacturers recommend the use of kiln cement for repairs, and while many of these products are good and will work, over time bricks will move/shrink and the cement may work itself loose and you could end up having this on you products, especially if applied to the roof of your kiln.

Steps for pinning bricks:

1. Ensure your kiln is switched OFF.
2. First ensure you have some brick pins. Brick pin are made from element wire (anything from 2.4mm to 3mm in thickness), and are cut into lengths of +/- 100mm. Never use normal wire as this will melt!
3. Reposition your brick back in place or, if it is a replacement brick, position where you would like it. Ensure that the bricks fit snuggly into each other. The tighter the fit the better.
4. The aim of pinning bricks is to get a good hold into the surrounding bricks.
5. Using some thin nose pilers, hold the pin and push it into the brick at a 45 Deg angle (note: insolation bricks are soft and no excessive force is required). The intention is to have the pin flush with the brick. NB – Ensure when you are pinning near an element do not let the pin touch the element or the outer casing (normally metal sheeting) of the kiln, the reason for this is you do not want to create an earth leakage that could trip your fuse breaker. NB – your elements carry electricity.