Why You Need to Use Kiln Wash

Kiln wash is a blend of refractory materials, commonly kaolin and silica, mixed with water into a thin slurry. Because it has a higher melting point than most glazes, it stays as a dry barrier at firing temperature.

Glaze is essentially molten glass. At high temperature it becomes fluid and bonds aggressively to porous surfaces.

• The barrier: If glaze runs or drips, it fuses to the kiln wash instead of the shelf.
• The cleanup: After cooling, the glaze and the underlying wash can be scraped off, leaving the shelf intact.

Even with stable glazes, kiln wash helps prevent clay bodies from sticking to the shelf during firing.

• Thermal expansion: At high heat, some clay bodies can become slightly tacky. A barrier prevents sticking and surface pitting.
• High fire stoneware: In Cone 6 to 10 firings, the clay shelf interaction can be more volatile. Fresh wash helps pieces release cleanly.

A good kiln wash job is thin, even, and applied in the right places.

• Top side only: Do not apply wash to the bottom of shelves. Flakes can fall onto ware below and ruin glazes.
• Rule of three: Apply 2 to 3 very thin coats instead of one thick coat. Let each coat dry before the next to reduce cracking.
• Clear the edges: Leave about a half inch border uncoated to reduce flaking and keep debris away from elements and ware.

• Scrape and reapply: Check shelves before every load. If wash is cracked, flaking, or has glaze drips, scrape the area and patch with fresh wash.
• Shelf rotation: Periodically remove old wash and flip shelves to help counter natural sagging or warping over time.
• Respiratory protection: Scraping kiln wash creates fine dust. Wear a properly fitted NIOSH approved N95 or P100 respirator when cleaning shelves.
• Extra protection: For runny or crystalline glazes, use catch trays or cookies under ware for another sacrificial layer.