Hot glass will stick to most ceramic or metal surfaces and crack as it cools, unless prevented by a separator like Bullseye shelf primer. Careful application of this primer to shelves and moulds will result in smooth, effective firing surfaces.
Mix 1 part shelf primer powder to 5 parts (by volume) of water. Apply five coats of primer, in a cross-hatched fashion. A Chinese haik brush (product 950.207) is ideal for this purpose. Ensure you stir the mix frequently during application to stop the powder settling. Dry the shelf/mould in your kiln at approx. 260ᵒC (500ᵒF) for 20 minutes. Then allow to cool to room temperature before use.
Frequency of cleaning and re-application will depend upon firing temperature. Firing at lower temperatures will enable you to reuse the shelf/mould several times provided the primer is not scratched. When necessary, remove old primer and re-coat as before.
Store shelf primer powder in a tightly closed container in a cool, dry place. Primer that is mixed with water will last for several weeks, if kept covered.
Avoid breathing shelf primer dust; wear a respirator such as 980.352.