Firing your kiln is really simple, but there are so many variables and factors that come into play that one should not take anything for granted.
There are many types of kilns and several types of firing processes. Here we will primarily address the basics of firing and address specific types and situations in separate articles.
Newer kilns have computerized digital controls which is pretty much just a matter of setting and forgetting. These will be discussed another time.
Older kiln styles are either manual or come equipped with kiln sitters and/or timers. Some people with manual kilns will use Guide Cones and/or pyrometers to help control temperatures. A timer is used as a back up to help prevent over firing and meltdowns.
Pyrometers are also used in the place of kiln sitters and timers.
For the sake of this discussion, a kiln equipped with both a sitter and timer will be point of reference
Before loading and starting the kiln, the operator needs to know what the purpose of the firing is. The following are most common firing purposes. Greenware, Glaze, and Overglazes. Within each of these are additional considerations, for example: Greenware - Will the items be used for utility purposes, decorative only, will they be glazed or will they be stained. Glaze – do the instructions tell you what cone to fire and what cone was used to fire the greenware; Overglazes – are you firing gold, decals, lusters, china paints? Each of these things requires different temperatures or cones. (see article about cones)
So let’s begin. The first thing is to prepare your kiln. You should make sure the kiln chamber is free of dust and particles. A shop vac is a worthwhile investment. Next, make sure you have applied one or two coats of Kiln wash to the surface of all shelves, the bottom of the kiln chamber and I recommend the ends of your posts. I also encourage brushing some on the top of the two bottom 'sitter' prongs. (Not the movable rod) Some companies say do this, others say do not. In any case, clean the prongs with a file periodically so there is no buildup on them from the cones. It is important they be kept clean. DO NOT put kiln wash on the sides of your kiln or the lid. You just need to let the application dry, it will cure during its first fire. You only have to do this once, unless for some reason you have to sandblast off glaze drips etc. at some later time.
When not using your shelves stack them so the washed sides are facing each other.
The kiln wash helps to prevent any glazes from fusing to your kiln furniture. If drops of glaze melt on anything, they can be removed a lot more easily than if you don’t use kiln wash. Kiln furniture is expensive and it is well worth the time to make this preparation.
Now your kiln is ready to fire. It is a good idea to test fire your kiln with a fast fire to calibrate that the sitter will shut off at the appropriate time. To do this, all you need to do is put a low temp cone, like 018 in the sitter, turn the empty kiln on high, set the timer for about 1 ½ hour, shut the lid and let the kiln fire until it shuts off. This should take about an hour (depending upon the size of the kiln). When cool, remove the cone and make sure it melted properly. If it is shaped somewhat like an ‘L’, your kiln is calibrated appropriately. If the angle is sharper, more like a “V” or a “U” your kiln is over-firing. If the angle did not reach an “L” shape, then the kiln is under firing. If your kiln is under-firing or over-firing, you will need to calibrate it before attempting to fire any of your ware.