Electric Hobby Kilns, How Good Are They?
Section: Firing, Subsection: General
Description
Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, but if you are aware of the limitations and take precautions they are workable.
Article
Firing an electric kiln is like using a microwave oven, right? Just slap the ware in, slam the lid, turn the switches on, 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. You have something that is fragile, hard to control, difficult to maintain, fires unevenly, and is an energy hog! Firing consistency is difficult with a good kiln; it’s really hard with one of these. Don’t get me wrong. Hobby kilns are great for earthenware and slip cast ceramics. They have also given many people the opportunity to get into stoneware pottery and porcelain, and even small scale manufacturing. But make no mistake, producing consistent ware will be a matter of developing a feel for what is happening inside and learning to compensate for the shortcomings.
Consider some specific points about making these contraptions work:
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When firing electric periodic kilns, you must get to know how to use cones properly (see the chapter on Cones). Mechanical sitter devices are not accurate unless they are kept in proper adjustment (the rod and supports bend a little with each firing). Since few people do this, it is better to treat them as fail-safe devices. Use a timer and stay within earshot of the kiln as it nears completion and use manual override to finish the firing if necessary.
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Electric kilns fire very unevenly as a result of compartmentalization created by full kiln shelves, elements of differing efficiency, uneven distribution of ware and kiln furniture, improperly sealed lid, and lack of draft. Set cones to be visible in peep holes on all levels of the kiln so you can adjust individual switches during the final stages to counteract. Also, use as little kiln furniture as possible, distribute it evenly throughout the chamber, and use half shelves where practical.
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It is best to fire as low as possible to minimize energy consumption and firing time. Remember, exceptionally strong ware can be made even at cone 1 and weak ware can be made at cone 12. A good approach is to develop glaze formulation and adjustment ability at your current temperature for a few years, then use this knowledge to gradually move downward. With effort, you can reduce firing temperature while increasing ware strength and going easier on your kiln.
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What really matters is not how much heat the kiln produces, or even how much heat-work the cones indicate, but how much heat the ware absorbs. It is thus easy to appreciate the wisdom of placing the cones with the ware, insulating them from the shelf and away from the elements so you can be confident that they represent the ware. Remember, an electric kiln has no draft so it is very likely that center sections will not be as hot as outer areas. A large bowl or sculptural piece that fills the chamber wall-to-wall will experience the kiln’s entire horizontal heat gradient. Firing slowly will ease these situations. Better yet, create some airflow with a kiln vent.
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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! An electric kiln has no draft to remove pore and crystal water so temperatures can generate an extremely humid atmosphere which retards drying of thick pieces. If ware isn’t dry when the really hot air starts to hit you know what happens! If possible, get a dedicated drier.
Here are a few other suggestions:
- Use a thin layer of insulating blanket between the kiln lid and top edge to minimize heat loss from poor lid fit.
- If you can possibly afford an electronic kiln sitter, then get one. These devices go a long way to overcoming shortcomings of hobby kilns.
- 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 rather than a metal grate that will 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.
Hobby kilns are not so bad after all. Like so many other things in ceramics, limitations can be compensated for by experience and care. And if you are serious, take a look at an industrial kiln as soon as you can. •
Authors
- Tony Hansen (Owner)
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