The primary purpose of Kiln Shelf Wash is to prevent your glaze from sticking to the kiln shelf, should it come in contact with it during firing. Kiln shelves are normally made of hard ceramic, just like your pots, so if glaze melts directly onto a kiln shelf, it will stick!
For use of shelf wash you mix it 1:1 with water till it’s like a thin glaze consistency.
Paint it on one side of the shelf horizontally and then another coat vertically.
After the initial coat, let the kiln wash dry and apply additional coats until the thickness is about 1.5mm.
Let each layer dry in between coats. If kiln wash is applied too thickly, it will flake off and chip more readily.
During the first application, we recommend applying 2 coats, firing the shelf and then applying a third.
You don't have to do a special firing just to fire those first two coats; load the shelves with bisque work and you will be good to go!