Kiln wash

Kiln wash is a thin, dry, chalky coating painted onto the tops of kiln shelves before glaze firings. Made typically from a blend of kaolin clay and silica, sometimes with a small amount of alumina, it forms a protective, slightly powdery barrier between the shelf and anything that might drip, run, or crawl off a pot during the firing when glazes turn to liquid glass at peak temperature.

Without kiln wash, a single glaze drip fuses permanently to the bare shelf, ruining a section of otherwise expensive kiln furniture and often taking a piece with it if it is glued down hard enough to crack on removal. Kiln wash sacrifices itself instead, since a dried glaze drip can usually be chipped off the wash layer with the wash then patched or reapplied, protecting the shelf underneath indefinitely with normal upkeep rather than one time use.

Applying it is straightforward, mix the powder with water to a thin cream, brush on a couple of even coats letting each dry, and avoid painting it right to every edge since flaking kiln wash dust can land on nearby glazed pots and cause small blemishes. Shelves should be kiln washed on a schedule rather than only after a drip happens, and any pot with unglazed clay on its foot still needs to sit clear of bare kiln wash contact in some cases, so checking specific shelf and stilt recommendations for a particular kiln setup is worth the few extra minutes.