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Selecting an Electric Kiln

by Ken Shelton

Published: January 2012

Buying a new kiln is a big step, whether you are a beginner or established potter, it is a substantial cost and you need to answer a host of questions if you are to ensure that you make the best choice. I have summarised some of the most important points here; there will be many other considerations, but hopefully this might act as a checklist to start you off in the process.

Shape and Size
What are the size, shapes and quantity of the work that you make now and how might it change in the future. Tall sculptural work clearly needs a firing chamber with at least an inch or two to spare in height. Large flatter work, plates, bowls etc need a kiln with a wider chamber and, if items are to be fired on more than one shelf, the crucial measurement is the space left after props supporting the shelf above have been put in place. There is not always a huge difference in cost for the next size up, so my advice  is usually to go for the biggest kiln you can.

Top or front loading
No longer are top loaders seen as lightweight, hobby kilns, times have changed and advances in materials and engineering have produced very robust kilns. Companies like Potterycrafts have been at the forefront in recent years with   a complete redesign of their top loading range. At their Stoke-on-Trent factory they have concentrated on producing kilns with strength and economy to satisfy professional potters while keeping the prices realistic for the amateur.     There is little to choose between a Potterycrafts top loader and their front loaders  in respect of quality; when the door is closed the bricks and elements are the same. Front loading kilns must have a more rigid, heavier construction to support the weight of the door as     it swings open; this of course makes them more expensive. Where there is heavy usage, for example in schools, colleges and production potteries, the preference is often for a front loader. 

Program controller
Program controllers are the instruments that control the rate of heating, the top temperature and if required the rate of cooling. Kilns are offered with a number of options for controllers, if firing to only one temperature, a simple single program controller will suffice; if a number of different program are used a multi-program controller is recommended.
A simple controller may only offer two rates of heating, a hold (or soak) at top temperature and cut-off. For more controlled firings instruments with many different segments in each program are available, this enables a more efficient use of power and a more gentle and accurate firing for the pottery. It is essential that the controller has safety features such as over-temperature safety cut-off to protect against over-fire, anti-surge to protect against electrical power surge that could damage the electronics and diagnostics to inform you of problems found in the firing. 

Ceramics, Glass and Enamelling
Most electric kilns can be used equally well for glass slumping, fusing and annealing; in fact much of the slumped and fused glass on the market is produced in pottery kilns. Where large work such as panels for architectural applications are  being produced it is preferable to use a designated glass kiln. These are a “flat bed” construction and provide a large flat area with heating elements in the roof, spaced to provide an even distribution of heat over the work. The crucial point with using pottery kilns for glass is to have the right type of controller. As discussed above, simple ceramics programs require controlled heating and power cut-off; however glass work requires additional control  of the cooling cycle through the annealing phase. Annealing is where the stresses of the process are relieved by very specific cooling rates; sometimes several stages of cooling to different temperatures are required. This necessitates the use of a controller with many segments in each program, these are often used for more sophisticated ceramics programs as well, so there is no problem with fitting multi-segment controllers to a pottery kiln. There is a price difference, but you would typically pay something under than £100 for these controllers. Pottery kilns can also be used for enamelling in so far      as they can provide the necessary heat and control, but    it is better to use a specific enamelling kiln such as manufactured by kiln makers such as Potterycrafts.  Enamelling processes are carried out at lower temperatures than ceramics, so the kilns need less insulation and are consequently significantly cheaper.

Positioning the kiln
It essential that you have plenty of space to load your kiln and that there is some room around it for airflow, usual advice is to allow 20/30cm between the sides and adjacent walls. With front loading kiln you will need extra space behind the kiln to allow access for maintenance, 45cm is usually sufficient. Do also check door widths to ensure the kiln will pass through. In domestic situations kilns are often housed in garages or outhouses, even wooden garden sheds. It is of course vital to ensure the conditions are dry and no combustible materials are touching or near to the kiln, fireproof materials may be used to eliminate any risk to floor, walls and ceiling.

Power supply
It is vital that you check available power supply before making a decision. Only the smallest kilns can be plugged in to a domestic 13 amp, three pin socket. Larger sizes will need to be wired in like a cooker. Most popular sizes of craft kiln can be run off a “cooker socket” but you will need to check with an electrician and get a quotation as installing a new supply can sometimes be costly.

Health and Safety
Kilns are designed to contain heat, so even when serious over-fires occur (a very unusual event nowadays), the kiln is unlikely to become a fire hazard. Ensure that no combustible material is touching or near to the kiln. Although with electric kilns only low levels of fumes are generated, it is important to have an airflow through the kiln room, an open window may be sufficient. An electric extract fan is a good solution, but ensure that you have an open window, airbrick or some other source of replacement air or the fan will not work.  Whatever form of ventilation you have, do not work in the same room  as the kiln when it is firing.    

Servicing and spares
At some stage in the future your kiln will need servicing, elements replacing etc. Check out the backup offered with a new kiln; is there a quick supply of spares, are there service engineers available. Ask how much a replacement element set costs, there can be massive differences between makes. If considering a second hand kin check that the maker is still in business and that spares are available, even small repairs can be impossible or very costly if the correct parts are no  longer obtainable.

Ken Shelton
Potterycrafts Ltd.

Ken is a professional member of the Craft Potters Association and a technical consultant to Potterycrafts Ltd.

 
British Crafts at Blackthorpe Barn

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