How to use Kiln Wash
also called separator or shelf primer
Applying to a new shelf or mold.
- Use instructions below, except:
- Apply 5 coats on a new shelf or mold.
Applying to a previously coated shelf or mold.
- Mix 1 part powder with 5 parts of water.
- Remove old primer with non-loading sand paper (Item #FF). It does not have to be removed completely.
- Exception: If you have not fired over 1400º you can cheat and reuse shelves and molds several times without reapplying primer, provided the primer has not been scratched, chipped or is not flaking. But, to be safe, I advise putting a fresh coating every time you are doing a special firing that has taken you a long time to assemble, or where you have spent a lot of money on glass.
- Apply 4 coats on a new shelf or mold. We recommend using a Haik Brush. The small hairs that fall off the brush and stick to the shelf do not seem to affect a firing.
- Stir while you dip brush into your powder/water mixture. Make two brush strokes across the shelf, applying as evenly as possible, overlapping slightly. Re-dip brush and stroke twice again in the next area. Repeat until the whole surface is covered. This is your first coat. Now coat the surface again but at 90º, cross hatching the first coat. You do not have to let the surface dry between coats. Apply a total of 4 coats. After your final coat, dry completely in the hot sun or in the kiln at 500º F for 20 minutes. If the coating cracks an peals while drying in the kiln, it means the shelf was heated to fast. Clean and re-apply again and slow down the next time.
- The trick is to get the coating as smooth as possible. Applying these thin coating gives you a smoother surface. If the water evaporates from your mix, the mix becomes thicker and you will get some streaking on the shelf which will show on your finished fused pieces. You can create an effect using this technique, by making the mix even thicker and swirling the muddy mixture in a pattern which will show up on the back of the glass.
Tips On Shelf Preparation
Clean your shelf well before applying new shelf primer. Allow newly stirred liquid shelf primer to settle for a few moments before applying to the shelf. This allows the larger particles to sink to the bottom of the container. Avoid this "bottom sludge" when dipping your brush into the shelf primer. These thicker, undissolved particles more often stick to the glass on firing.
Preparing a Metal Mold
Metal, like most mold materials, needs a good coat of kiln wash to keep the glass from sticking to the mold. Unfortunately metal molds can be uncooperative in this regard. As fast as the kiln wash is brushed on it all runs to the bottom of the mold, leaving the sides bare
The trick in getting the kiln wash to stick to mold is to heat the metal to approximately 400° in your kiln (Do Not Overheat). Using gloves or tongs remove the mold from the kiln and place it on a nonflammable surface such as a kiln shelf. Working quickly before the metal cools, spray the kiln wash onto the mold using an airbrush or atomizer. Because the metal is hot the kiln wash dries before it has a chance to run
Wear a Dust Mask When Applying Kiln Wash
As soon as you begin to see wet spots in the metal, reheat the mold and repeat the spraying operation. It may take five or more reheating to achieve a good surface coating. For more information refer to the Fused Glass Handbook or Kiln Crafted Glass, Slumping Video