Some molds, notably those made of stainless steel, do not always respond to the room temperature brushing or spraying techniques that are used with ceramic and other items. As a result, you need to heat the stainless steel mold in order to get the kiln wash to stick.
To do this, place the stainless steel item inside the kiln. Leave the lid or door of the kiln open slightly, just in case any fumes build up and need to be vented. Then heat the kiln to a temperature of about 500 degrees F. Control the kiln so that this takes about half an hour. Taking longer is perfectly acceptable.
While the kiln is firing, prepare your kiln wash materials. You'll need some kiln wash and either a soft, wide brush or a sprayer or airbrush. Lay the items you will need on a surface that won't catch fire if something hot is placed on it.
You may use either a brush or a sprayer, but be aware that using a sprayer or airbrush on stainless steel molds will result in a smoother finish than using a brush. In addition, some artists also use a mask when mixing and spraying kiln wash. This keeps you from accidentally breathing in kiln wash particles, which can be harmful if inhaled.
Once the temperature in the kiln reaches 500 degrees, turn off the kiln. Put on your gloves, reach inside the kiln, and carefully remove the stainless steel item. Place it on the nonflammable surface, next to the kiln wash.
Spraying on kiln wash is a simple matter of applying a thin, even coat of kiln wash on the outside surface of the mold. The kiln wash will sizzle as it goes on. That's the sound of the water in the mixture evaporating and leaving the protective powder behind.
If you've decided to apply your kiln wash with a brush, make certain you've selected a brush that will resist the heat of the stainless steel. Foam brushes (and some haike brushes) will not work, but most good quality paint brushes can withstand the heat.
Quickly use the brush to apply the kiln wash. Cover all areas that might come into contact with the glass. As with a spray application, the kiln wash will sizzle as it goes on. Once the stainless steel item is covered with kiln wash, allow it to dry completely and return to room temperature. If you wish, you can return the mold to the still warm kiln to help it dry more quickly, or you can just let it air dry.
One application is often sufficient to cover the stainless steel item. If not, simply reheat and coat again. You may want to sand lightly between coats. Once the item is dry and room temperature cool, check to make sure that none of the air holes at the bottom have been filled with kiln wash and are in need of opening.
Some people rough up the surface of the mold prior to applying kiln wash to help it stick better. If you decide to do this, use very fine steel wool (000 works well) and make certain you wash the mold well before applying the kiln wash.
When you finish, the mold should be smooth to the touch, with no visible gaps or bumps. The kiln wash application should last for several firings, but if it flakes away, starts to look thin, or discolors slightly, you should reapply the kiln wash. For best results, lightly sand the mold with very fine steel wool before reapplying.
Many thanks to the Warm Glass website for posting this important information. Click here to read the Warm Glass website!