Depending whether you are doing a bisque firing or a glaze firing will depend on how you can load the kiln.
Bisque Firing
In a bisque firing you are turning clay to ceramic, therefore nothing you will have on your clay pieces has a chance to damage or contaminate any other pieces it may touch. In this firing you can stack as many pieces as you like together in a space - they can be stacked together e.g. bowls/flat slabs, each piece can touch each other from any angle, from the sides, the top or the bottom.
You can really load up a bisque kiln with as many pieces as you can possibly fit in. You need to remember that the more pieces you stack together and the more shelves you have will make the firing use more electricity and the price of electric to fire the kiln will be quite high.
The risks of stacking your work for a bisque firing is that at bone dry stage your pieces are extremely fragile and if you knock them they have a risk of smashing, so you have to be very delicate when handing bone dry pieces.
Glaze firing
A glaze firing is very different to a bisque - glaze pieces cannot touch each other, as the glaze starts to melt the pieces if they are touching would fuse together as one piece.
When you load the kiln you must handle the pieces very carefully. The glaze applied wet and dries in a powdery form, if you knock it it can chip off. If an area of glaze has chipped off and not reapplied once fired there will be an area on the ceramic piece with no glaze on.
Another thing you need to consider is whether the glaze could contaminate any other pieces that are in close proximity to it, this can happen depending on what ceramic materials make up the glaze. Gases can come out of the glaze and change the chemical reaction of another close by glazed piece.
A glaze can change depending where it is fired in the kiln. If you fire an identical piece one on the bottom shelf and one on the top there can be variants, it can also vary depending how much space is around the piece to how much air it has.
When loading up a glaze kiln you must leave at least a cm around each piece, this is so that is glaze runs that your pieces won’t be fused together. If you know the glaze you are using runs then you would leave more space or even fire it above sand, this would catch the glaze run and stop it sticking to the kiln shelf.
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