Interesting quote from Sundance Glass.
"The silver will easily stick to the glass.
Pure gold (24 ct) does not want to easily stick to the glass, so....... either
1) Put down a silver coating and then use the pure (24ct) on top of the silver coating OR
2) Use the less pure gold (22ct), the impurities will help the gold stick to the glass.
Each method will actually give you a slighty different effect."
http://www.sundanceglass.com/decaccesspyrex.htm