Trying to remove baked on kiln wash from the underside of a glass piece can be one of the most frustrating experiences for the warm glass artist. In the worst cases, it doesn't respond to elbow grease, it requires nasty chemicals, and it leaves an ugly stain behind.
But there's no need to despair, there are several ways to remove the baked on primer. Part one of this two-part tip deals with less aggressive, relatively simple and safe, methods of attacking the baked on kiln wash beast.
1. Vinegar. Soaking the glass in distilled white vinegar (a mild acid) for two to three hours will often help the kiln wash come off with a minimum of scrubbing.
2. Acid Etch or a similar etching product -- although this will leave a matte finish (not unattractive, by the way), a simple soak for ten to fifteen minutes will usually remove the kiln wash completely.
3. Old fashioned elbow grease -- either after soaking in water or vinegar, or just by itself. A good scrub with wet/dry sandpaper, Fabricut (open weave sand paper), or a similar product can work well.
This information was found on Warm Tips. Check out this web page for a lot of excellent warm glass hints and tips!