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The Importance of Kiln Wash: Article or Project

Kiln wash is a thin layer of minerals that are applied to ceramic shelves and furniture when kiln firing ceramics. Usually a powdered mix primarily of alumina and zirconium which is mixed to a thin consistency with water then applied to the chosen surfaces. Alumina and zirconium both have very high melting points. It is an inexpensive protection to prevent damage to costly kiln furniture.

Notice Photos, top right of page. First shows properly applied kiln wash to a shelf. Second shows Wash that was applied too thick as well as spots of glaze that dripped.

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The primary reason to use kiln wash is to protect your kiln from potential accidents during firing ceramics. Dripping glazes are of great concern. During firing they can bubble up and explode or jump off the ceramic surface, or if applied too heavily, it can drip onto the shelf, or an item tips over .

One other thing that can damage your kiln is if you have a melt-down. This is when your kiln fires too hot, has a sitter or cone failure or fails to shut down when it should. In all of these cases, when the kiln cools, the glazes and glazed items become fused to the kiln surfaces.

Of course, using stilts under ceramic items can help save your shelves and should be used on all glazed items -but not in all cases. However, when you fire pottery, stoneware or porcelain, they are fired dry-foot, meaning there is no glaze applied to the bottoms. They melt at high temperatures, therefore, there is no stilt ergo there is a higher risk of glaze accidents.

Kiln wash should be applied to:

one side of the kiln shelves,
the bottom of the kiln,
the ends of the posts, and
on the two NON-MOVABLE prongs of the kiln/cone sitter.

DO NOT put wash on the movable prong.
DO NOT put wash on the side walls of your kiln.
DO NOT put wash on the lid (underside) of the kiln,
DO NOT put wash on the sides of the shelves.
DO NOT put wash on both top AND bottom of the shelves (Just one or the other)

Kiln wash is easy to apply. Take a small amount of the powder and add enough water to make a thin consistency (like skim milk). It is important that the wash be applied in thin layers for a smooth surface. If the wash builds up, it can cause things to sit crookedly and even tip over at some point.

Use a large brush and work quickly. Spread the wash thinly to cover the surface working to make sure there are no brush strokes or build-up.

Let the first layer dry thoroughly. (Option fire the shelf or stilts etc to harden the washed surfaces between coats).

Similarly, apply a second coat of wash and if you desire, apply a third – drying between coats.

Once fired, the washed surface becomes semi permanent. It will lift off or can be pried off should something stick. Once the item is removed, you can reapply wash to the affected area until such time as your surface becomes too uneven. If applied too thick, it can begin to chip off.

Over time with many firings, the wash can chip off. When the surface is no longer useful to protect your shelving etc or glaze drips prevent you from being able to use it with greenware or dry-footed items, you can sand it off with a strong sander – will take time and a lot of effort.
A good file can be used on the NON-movable prongs – again DO NOT put wash on the movable prong. The application of wash will help in the case of an over-fire if your cone melts around or sticks to the prongs.


NOW FOR SOME EXCEPTIONS. For Every rule, there is an exception and the laws for ceramics are no different.

DO NOT apply wash to fiber shelves, use special ceramic firing paper instead. This will have to be replaced with each firing

DO NOT apply wash to Nitride bonded silicon carbide shelves because generally glazes will not stick; however caution should be taken when using gas kilns and when firing porcelain


DO NOT apply wash to a kiln floor if there are elements on the floor

When firing glass for slumping etc, you should use firing paper or a special treated surface/form rather than directly on the shelf to prevent blemishes from imprinting through the glass. Slump or drape molds specifically geared for firing glass, should also be treated with two or three light coats of kiln wash.



 

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