Electric Hobby Kilns: What You Need to Know

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Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, being aware of the limitations and keeping them in good repair is very important.

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Firing an electric kiln is like using a microwave oven, right? Just slap the ware in, slam the lid, set the controller to cone fire, and take out the beautiful ware the next day. It is that simple isn't it? Not quite! If you are using a top loading hobby electric kiln for stoneware pottery, it is good to be aware of what you have. Compared to industrial electric kilns, you have something that is fragile, hard to control, difficult to maintain, fires unevenly, has little or no ventilation and is an energy hog! It has no element holders, no draft, a heat leaking lid, bulky energy-stealing kiln furniture and a toy controller. Yet hobby kilns have proven great for earthenware and slip cast ceramics that do not require tight control and they have also given many people the opportunity to get into stoneware pottery and porcelain, and even small scale manufacturing. Producing somewhat consistent ware will be a matter of learning to program the up and down temperature ramps to compensate the amount of ware in the chamber with the inaccuracy of the pyrometer and the condition of the elements. Uptime will depend on being vigilant about maintenance (e.g. replacing relays, thermocouples, elements as needed). Before getting too depressed, it is possible to do amazing things: Crystalline glazes for example were once the domain of a select few, but now they are simple because of these devices.

Consider some specific points about making these contraptions work:

Modern electric hobby kilns have electronic controllers. This sounds impressive at first, but in some ways it is an efficient method to automate failure. You still need to think about what is the best firing schedule for your type of ware and implement it in a way the kiln hardware is capable of reproducing (for both up and down ramps). And you need to monitor it well to be sure of ongoing accurate reproduction, because, in ceramics, lack of consistency in firing will certainly bring issues. Your kiln depends on the thermocouple to know what the temperature is and the elements to heat it up. As already noted, components are consumer-grade, they have their limits and need maintenance and replacement regularly. Mechanical sitter devices introduce even more things that need maintenance and adjustment (the rod and supports bend a little with each firing).
Use cones. Consistently accurate firings will not happen if you do not use traditional cones. They tell you what firing you actually got, giving the information you need to compensate the firing program. Their presence in firing after firing will tell you when the thermocouple is starting to stray or alert you to other issues. Of course, make sure the cones are set at the right angle and away from close proximity to elements (self supporting cones are by far the best).
Document your firing schedules and stick to them. Adjust and perfect them over time as you get to understand your process better. Using the schedule manager at Insight-live.com you can accurately predict when your firings will end (provided no part of the schedule climbs faster than what the elements can accomplish even at the poorest condition you allow them to deteriorate to). At Plainsman Clays, we have found that we can predict the end of firings from cone 06 to 11 to within 5 minutes! When you can do this you can monitor the kiln and override it if necessary (to finish early or continue if the cone has not fallen to the proper angle).
Electric kilns fire very unevenly as a result of compartmentalization created by full kiln shelves that reach to nearly the edge of the chamber, elements of differing efficiency, uneven distribution of ware and kiln furniture, improperly sealed lid, poor insulation, lack of draft and the high ratio of shelf-weight to ware-weight. You can improve things by having a controller that compensates zones or by setting cones to be visible in peep holes on all levels of the kiln and stacking future firings with this in mind. Also, use as little kiln furniture as possible, distribute it evenly throughout the chamber, and use half shelves where practical (to prevent the compartmentalization). But even with all this, heavy ware cannot be fired evenly no matter how long you soak the kiln. That is because electric kilns heat via radiation and the shady side away from the elements is always going to be cooler than the element side.
As noted, hobby kilns are poorly insulated. A typical potter thinks that 2350F is really hot because his/her kiln has to struggle so much to get that high. But kilns can go much higher (e.g. 2800F). How? Better refractories. Better bricks, thicker walls, ceramic fiber, etc. Industrial kilns are light-years ahead of hobby kilns in this area. All of this being said, since hobby kilns do not have forced ventilation it would not be possible to fast-cool them evenly if they were better insulated, so they are what they are!
In industry, the final pore water is removed quickly and evenly from ware in drying chambers that employ boiling-point temperatures and very stiff humidity controlled drafts. I'm guessing you use your kiln for this during early stages of firing! As mentioned, an electric kiln has little or no draft to remove pore and crystal water so temperatures can generate a humid atmosphere that retards drying of thick pieces. If ware isn't dry when the really hot air starts to hit you know what happens! A dedicated drier is the norm in industry but not usually an option for potters, so the only alternative is to heat slowly at the low end (we hold the temperature at 250F for hours if needed).
Fire slower and soak at the end. Firings will be more even, consistent, ware will be better quality, glazes will have less imperfections. This is especially true if you are firing a heavy mass of ware. If you fire too quickly and do not soak at the end of the firing, the ware simply will not reach temperature (even though cones or instruments may indicate otherwise). The color of stoneware clays typically varies with temperature, often from a yellowy straw color to a grey (or light red to dark red, then brown). Thus you can compare the color of the raw clay (or clear glazed) surface on a light thin piece with a heavy thick one (or the shady side of a heavy piece with the element side). Differences in color indicate differences in maturity.
Electric kilns really shine at low to medium temperatures where it is possible to create high strength stoneware bodies. "Stoneware" is simply dense and strong non-pourous ceramic. It is no longer synonymous with cone 10, it can be made as low as cone 1. However it is more difficult to create low-fire glazes that are non-leaching, hard and uncrazed. Matte glazes are easy to make at cone 10, but more difficult at medium temperature oxidation. And very difficult at low temperatures. Glazes at high temperature have lots of clay and the slurry suspends well, but at lower temperatures more flux is needed, that means less clay and more problems with the slurry and application. Materials that melt well a high temperatures (e.g. dolomite, talc, feldspar, whiting) melt poorly or not at all at middle and low temperatures. Boron is the king of fluxes at medium and low temperatures, glazes need it to melt. It is sourced from frits and natural boron materials like gerstley borate, ulexite and colemanite.
Can you fire even lower? Since it is possible to produce stoneware as low as cone 02. On the one hand, there is not as much knowledge about low fire glazes, they are more difficult to fit to bodies, there are fewer natural materials that melt that low and there are fewer mechanisms that create interesting glazes. On the other hand, tons of low-melting frits exist and low-fire glazes are brighter and stains work well. Frit-ware bodies are awesome (e.g. check our Zero3 body and glaze) and enable stoneware even lower. There are methods to variegate the glazes chemically, artificially and physically. Some industries have achieved dramatic reductions in cost by going low.
Make sure the lid of your kiln is sealing well all the way around. When changing elements, do them all at once when possible. Also, make sure the switches are well ventilated or they will overheat and fail. If your kiln has a solid metal top on the switch housing (with no vents or metal grate to allow air passage), it is a prime candidate for burning out switches.
Electric kilns are fragile, so treat them with care. When changing elements, you can minimize brick damage by turning the kiln on for a few minutes, then unplugging it and pulling the otherwise brittle elements out while they are hot and flexible. When installing, read the instructions carefully and use good crimp or screw connectors. It is really important to make sure the elements are not stretched into the groves, they must sit in there under no tension and be bent to stay in the corners (if not, they will sag out during the firings). High quality electric kilns for industry have always been available and their element mounting systems are far superior to the way electric hobby kilns work, but we make do!
Ventilation Systems: These not only make kilns safer to use but they introduce draft, a key to improved fired results (if the interior of the kiln can be kept at even temperatures throughout). When products of decomposition are removed quickly during firing (especially carbon, sulfur) results are much better and problems are fewer.

Hobby kilns are not so bad after all. Like so many other things in ceramics, limitations can be compensated for by experience and care. If you get richer some day, take a look at an industrial grade electric kiln, they are amazing.

Should you get a gas kiln instead? If you get really rich it is an option, but be prepared for quadruple the price! And installation hassles and costs that could double that again! At cone 10 high temperatures are "on your side", all the common ceramic materials melt easily so you don't have to fiddle with frits or boron. Bodies and glazes are less expensive. Glazes seem to just fit bodies naturally. Ware durability is almost a given. That being said, gas kilns require more expertise and dedication to fire and willingness to lose loads of ware during the learning period (when fired wrong neither the temperature or reduction atmosphere distributes evenly). It is possible to spend $50,000 or $100,000 and not be able to get it working! It is definitely best to buy one through you local ceramic supplier to get their support. You will know that other customers are using it successfully and learn details about by-laws and installation issues. I personally have a cone 10 reduction kiln. But, strangely, I do hundreds of electric firings for every gas firing.