Kiln Firing for the Twitchy Art Teacher
*Disclaimer: This article is not meant to replace your kiln manual or establishment's procedures - I'm just here to give you some helpful tips and maybe a snicker or two!*
The kiln. For some, it is a holy grail instrument sent from the heavens to enhance the art program to another level of professionalism. For others, it's a mysterious machine as scary as the haunted basement furnace in Home Alone. Kilns also appear in a wide range of wear and tear, from rusty, melted, cone-sitting, glaze-covered, chipped and corroded ancient artifacts to glorious, shining, automated robots of the future. As art teachers, we may have had limited experience in ceramics entirely or we may have fired electric, gas, raku, and wood kilns alike. So, what to do if you are the former and staring down your own classroom kiln? Here are my suggestions for the first places to start:
Find Your New BFFs
A kiln is a bit like a stumpy-legged animal with its own personality. When encountering a new one, it's best if you can talk with someone who has tangled with the beast previously. Check with former art teachers in the building or the wider department. They may be able to tell you about misfiring, cold spots, programs to use, quirks, and other insider information. Also discuss it with your administration. Some building principals or superintendents have specific guidelines they must or prefer to follow. These guidelines might include when firing can happen and who needs to be there, specifics about the room (doors open or closed, how venting works, heat sensors, presence of students), and any other tidbits or stories of mishaps from years gone by. Last but certainly not least, talk to your custodian or maintenance department. They are frequently partners in monitoring kiln firing and potentially upkeep. Keep in mind that a firing schedule can last for 12 hours or longer...you'll want a buddy or two at school at various hours!
Find Your Kiln Manual
If at all possible, scour your room or the internet for your kiln model's manual. This will tell you exactly how to program firing schedules, maintain the elements, and click hinges, flip switches, and vent peepholes. If for some reason you are unable to find the manual, there can often be really helpful advice in art educator social media groups. Probing this hive mind is also helpful when seeking advice on firing specific projects based on thickness, building style, size, and time constraints. These are the people who can give you their own first hand experience.
Not all clay and glaze is created equal! Although it's likely that the materials in an art room will be dedicated to one type of firing, you will still want to know if your clay and glaze is low fire, high fire, or even raku. Low fire clay and glaze goes to around cone 06-04 while higher fire clay and glaze goes to cone 5-10. If a low fire clay or glaze goes into a high fire firing, it will melt all over the kiln. If a high fire clay or glaze goes into a low fire firing, it will be compromised in terms of durability or appearance. Clay boxes and glaze bottles should note what cone they fire to on the outside. Do not fire air-dry clay.
What I have done in a new art room is go through the ceramic supplies to clean and organize them. This lets me see what inventory is like, what the firing temperatures will be, and I am able to separate underglazes from overglazes, food safe from decorative. I also like to give the clay bags a good poke to see if I will need to re-hydrate anything or allow additional drying time for the clay before using it.
Brush Up on Firing Basics
There is a wealth of information on basic kiln firing online, and any good guide should run through pyrometric cones (05 vs. 5), different stages of clay (greenware, leather hard, bone dry, bisqueware), odd smells, and intense glows.
In general and quite briefly, the more you can let greenware clay dry before firing it into bisqueware, the less likely it is to explode in firing. The thicker it is, the more likely it is to trap moisture and explode or crack. If greenware is still cold to the touch, it has moisture inside. My rule is for students to make the clay no thicker than a thumb and no thinner than a pinky or pencil.
When loading the kiln, organization is key. While you will likely have student names or initials and a class abbreviation on the work, it helps tremendously to keep these grouped inside the kiln as well. When adding another shelf into the kiln, stack the stilts for the next level directly on top of the first set of stilts. If you have particularly tall works, save these for the top shelf of the kiln rather than trying to make a tall bottom shelf to accommodate them. Be sure that no kiln furniture or works are touching the thermocouple. Try to load the kiln evenly from side to side and top to bottom, while keeping in mind that bisqueware can touch, but glazed works need to have space between them (and no glaze on their bottoms!).
Typically if you are doing a low fire firing, the bisque firing (first firing) will be up to cone 04, and the glaze firing (second, if occurring) will be to cone 05. The reason for this is that the hotter cone 04 firing will burn out more contaminants that can mar a glaze surface (which happens at the lower 05 temperature). The more slowly you can fire, the less likely it is that pieces will explode. The more slowly the kiln is allowed to cool, the less likely that cracking or other glaze problems will occur.
When a kiln is firing, there will be intermittent clicking and buzzing. This is from the different elements turning on and off to heat the kiln to the appropriate temperature. When the kiln begins to get really hot, you will likely see a red glow shining just under the lid. If it is an automatic kiln, you will see the current temperature displayed on the panel. More information about what the display abbreviations mean can be found in the manual.
Health and Safety
The more you know about your kiln, and the more you get a few firings under your belt, the more comfortable you will feel. Regardless, there are certain safety measures that should always be taken.
Always vent the kiln. This keeps contaminants out of your air and helps to manage the heat that can be thrown off the kiln. Don't open the kiln before it is reasonably cool. Kilns get way hotter than a kitchen oven, and opening it early can not only ruin pieces, but it can set off heat sensors in the school and even burn you. To that end, keep the students away from a hot or firing kiln. Sometimes this will be easy as you may have your own kiln room, and other times you will have to set up a little guard around the kiln if it is sharing your space.
Do not look into a hot kiln without safety goggles. Really there shouldn't be much need to do this when firing an electric kiln, even if you are curious about whether or not something exploded. All will be revealed in time!
Keep a clean kiln. This means chipping off any glaze blobs from shelves and re-coating them with kiln wash, as well as sweeping out any pieces of exploded bisqueware from inside the kiln. While you are doing this, you can check to make sure the elements are not sagging and the softbrick is in good shape.
Allow a kiln to cool as much as you can before unloading it. Check the pieces for any sharp edges and use a file or grinder to make them blunt so that no one gets cut by accident. In the event of breakage, I have had decent luck gluing works back together (hot glue on bare clay is the easiest, though perhaps not the most elegant solution).
When in doubt, ask. If you have a question, try not to feel embarrassed. No one can know everything! Good luck!
What to do? What to do?
Simple handbuilding techniques
Simple handbuilding techniques
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