The main reasons that kiln wash sticks to glass are:
1. Firing at too high a temperature. The higher the temperature, the more likely the kiln wash will stick to the glass.
2. Firing with opalescent glass against the shelf. Kiln wash sticks to opalescent glasses more easily than to transparent glass.
3. Re-using kiln washed shelves that have been to fusing temperatures already.
4. Using kiln wash with high amounts of china clay makes for more sticking. Thus some brands stick more frequently than others.
Firing at too high a temperature is probably the worse culprit. The second is using opalescent directly on the kiln shelf.
Strategies to avoid this sticking are:
1. Fire at the lowest temperature you can to get the result you want. This often requires slow rates of advance and extended soaks at the working temperature
2. Use Bullseye kiln wash. It is among the best.
3. Have a transparent glass as the bottom layer.
4. Use iridised glass, with the iridised side down to the shelf, as the iridisation acts as a separator. Do not do this with Thinfire, as it can lead to large cavities in the glass. Fire onto kiln wash.
There are ways to get the kiln wash off but it's easier to avoid it. Using an iridised sheet on the bottom is probably the most effective prevention.