Electric Hobby Kilns: What You Need to Know

Description

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 some things. Compared to industrial electric kilns, these kilns are fragile, hard to control, difficult to maintain, fire unevenly, have little or no ventilation and are an energy hog! They have 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. It is still necessary 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). Close monitoring is needed to be sure of ongoing accurate reproduction, because, in ceramics, lack of consistency in firing will certainly bring issues. The 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 with traditional cones. Cones indicate what firing actually happened, which is valuable information to compensate the firing program. Their presence in firing after firing will indicate when the thermocouple is starting to stray or alert you to other issues. Self-supporting cones are by far the best.
Document firing schedules and stick to them. Adjust and perfect them over time. The schedule manager in Insight-live.com enables accurately predicting when firings will end (provided no part of the schedule climbs faster than what the elements can deliver). At Plainsman Clays, we have found that we can predict the end of firings from cone 06 to 11 to within 5 minutes! For the most accurate firing, this is valuable because it enables overriding when 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. A controller that compensates zones can improve matters. Setting cones to be visible in peepholes on all levels of the kiln also enables stacking future firings with this in mind. 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 the kiln is held at temperature. 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 2200F 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). Industrial kilns are light-years ahead of hobby kilns. Better refractories. Better bricks, thicker walls, ceramic fiber, better elements, more elements, etc. 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. Pottery kilns simply use the early stages of firing to dry ware. As mentioned, an electric kiln has little or no draft to remove pore (and crystal water) so a humid atmosphere persists, even where ware starts to get really hot. 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 when firing a heavy mass of ware. Firing too quickly and not soaking at the end of the firing means the ware simply will not reach temperature (even though cones or instruments may indicate otherwise). Since the color of stoneware clays typically varies with temperature, comparing the color of unglazed surfaces on light thin pieces with heavy thick ones will indicate differences in maturity.
Smaller electric hobby kilns shine at lower temperatures (e.g. cone 04-2). Elements can endure a thousand firings on adequately powered kilns. Conversely, the elements and relays in larger electric kilns that are usually fired full might only last 100 firings.
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 switches (on older style kilns) are well-ventilated or they will overheat and fail (kilns lacking venting on the switch housings are prime candidates for burning out switches).
Electric kilns are fragile, so treat them with care. When changing elements, use a plumbers torch to soften elements to they pull out of groove corners without damaging bricks. When installing: Read the instructions carefully, use good crimp or screw connectors, and quality tools. Make sure the elements are not stretched into the groves, under no tension and be bent to stay in the corners.
Ventilation Systems: These 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, care and an electronic controller.

Should you get a gas kiln instead? 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 frits are not needed. 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. Since there is a danger of spending $50,000 and running into serious issues it is best to buy one through your local ceramic supplier to get their support. A big advantage of this is being sure about by-laws and installation issues.