The Most Important Kiln Maintenance Habit
Kiln wash is a refractory coating applied to the top surface of kiln shelves. Its sole purpose: to stop dripping or running glaze from fusing permanently to the shelf. Without it, a single glaze drip can ruin a shelf, and removing fused glaze from a kiln shelf is a grinding, dusty, miserable job.
What Kiln Wash Is Made Of
Kiln wash is typically a mixture of alumina hydrate and kaolin (china clay) mixed with water. These materials have a very high melting point and do not fuse to glaze, so even if glaze drips onto the wash, it can be chipped off cleanly after firing.
Applying Kiln Wash
- Mix the wash to a thin, creamy consistency, like paint.
- Apply two or three coats with a wide, soft brush to the top surface only. Never apply wash to the bottom of a shelf; it can flake off and land on pots below.
- Allow each coat to dry completely before the next.
- Apply wash to new shelves before their first use, and re-coat any bare patches after each firing.
Maintaining Shelves
- After each firing, inspect shelves for glaze drips. Chip them off with a scraper while still manageable. Left for multiple firings, drips build up and eventually damage the shelf.
- If kiln wash builds up too thick over many firings, it can crack and flake into pots. Grind off old wash periodically with an angle grinder (outside, with a respirator).
Pro Tip
Never apply kiln wash to the underside of shelves or to posts. Only the top surface of each shelf needs it.
Shelf Maintenance Routine
After each firing:
- Inspect wash for bare patches
- Remove fresh glaze drips early
- Recoat thin areas before next load
Routine maintenance extends shelf life and protects work.
Down the Rabbit Hole
Kiln wash protects against the same glaze-fusing chemistry described in the Wikipedia article on ceramic glaze, where molten glass bonds permanently to any unprotected surface. The alumina in kiln wash has an extremely high melting point, which is why it resists the vitrification process that makes glazes stick to everything they touch.
