Digitalfire Ceramics Technical Articles

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. 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! Hobby kilns are 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. 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 of these kilns.

Consider some specific points about making these contraptions work:

• Modern electric kilns have electronic controllers. This sounds impressive at first, but in some ways it is an efficient method to automate failure. The kiln still depends on the thermocouple to know what the temperature is and the elements to heat it up. Both have their limits and need maintenance and replacement regularly. A good example of the shortcoming of these controllers is the deterioration of elements: as this happens the device can no longer fire the the requested schedule, most users just ignore this truth and wonder why results are changing. Admittedly, electronic devices have the ability to control the cooling rate and soak of kilns, this is a major advance.

• Mechanical sitter devices introduce more things that need maintenance and adjustment (the rod and supports bend a little with each firing). Since few people do this many times they are little more than fail-safe devices. It is actually best to use a timer and stay within earshot of the kiln as it nears completion and use manual override to finish the firing if necessary (people who do this will testify to how seldom the device shuts the kiln off at the right time).

• When firing electric periodic kilns, you must get to know how to use cones properly, they are the only way to confirm what the kiln is actually doing.

• Electric kilns fire very unevenly as a result of compartmentalization created by full kiln shelves that reach to nearly the edge of the kiln chamber, elements of differing efficiency, uneven distribution of ware and kiln furniture, improperly sealed lid, and lack of draft. 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 so you do manual overrides as needed. Also, use as little kiln furniture as possible, distribute it evenly throughout the chamber, and use half shelves where practical.

• 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.

• 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 hobby kiln has little 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. Kiln vents create some airflow, but common sense shows that this airflow is restricted by full shelves.

• 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 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:

• Fire lower. Did I mention that you should fire lower? Since it is possible to produce stoneware as low as cone 1 why on earth would anyone fire to cone 10? It is because there is not as much knowledge about low fire glazes. Also, they are more difficult to fit to bodies and there are fewer natural materials that melt that low and there are few mechanisms that create interesting glazes. On the other hand, there are tons of frits that melt at low temperatures. Low fire glazes are brighter and stains work well. There are methods to variegate the glazes chemically, artificially and physically. Actually it is possible to do almost anything you want, you just need to understand a little glaze chemistry, have the ability to calculate a glazes formula and compare that with how it is firing in the kiln and be open to new decorating and application methods. If you have control of your bodies and glazes, then you have the freedom to move downward over time, adjusting current glazes and introducing new ones. Some industries have achieved dramatic reductions in cost by doing this.
• Make sure the lid of your kiln is sealing well all the way around.
• If you can possibly afford an electronic kiln sitter, then get one. These devices, although having problems, go a long way to overcoming shortcomings of hobby kilns.
• Get a kiln with porcelain element holders of some sort, these extend the life of the kiln and the elements fit and stay better.
• 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. 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 go into the corners well.

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 grade kiln as soon as you can, they are amazing.

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