Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc. It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.

There are many kiln wash recipes to choose from and it’s important to find the recipe that works best with your firing practices. What works well at one firing range or atmosphere, may not be well suited for another.

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A good wash requires materials that have very high melting points and that, when combined, do not create eutectics that cause melting. Kiln wash is used in the full range of ceramics firing from cone 022 to cone 14. The type needed varies for each specific situation because some potters work in electric kilns at low-fire temperatures, while others work with fuel-fired kilns at very high temperatures.

A common recipe for gas and electric oxidation or reduction kilns is 50% kaolin and 50% silica (flint). However, that mixture must never be used in salt, soda, and wood firing. For those processes, use 40% kaolin, 10% ball clay, and 50% alumina hydrate.

Mix kiln wash to a thick creamy consistency and apply with a wide brush or paint roller. In some cases you may wish to build up successive coats, especially in any situation where significant glaze runs are fairly common.

In all cases, avoid getting your wash on the edges of the shelves where it can flake off in the firing and fall on glaze wares below.

Source: Clay: A Studio Handbook Since this was expanded using text from another source, should we delete this? Or could we put it in the first paragraph like this:

Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc (Source: Clay: A Studio Handbook). It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.