Trial #2 on Opaque White

This example uses the same shapes and sizes of heavy copper foil, the same clear glass cap, but a different anchor piece.

Three layer trial - white, opaque, non-reactive COE 90, heavy copper foil, and narrow clear cap before entering kiln.

The white glass on the bottom of the triple layer is solid an opaque, but not labelled "reactive.  I did not expect it or the copper to show signs of chemically being effected by the other.

Three layer trial - white, opaque, non-reactive COE 90, heavy copper foil, and narrow clear cap after firing in kiln.

It was interesting to me that the copper in this "sandwich," has more variation in the coloring under the clear glass.  In the enlargement of the area around the star, seen below, the variations in the copper are more easily seen. 

Close up of three layer trial, specifically designed to study variations in copper coloration after firing.

It would be interesting to try several variation of base color, heavy copper foil and narrow clear cappers to see if the variations are a result of the base glass or can they be attributed to something else.
 
I have learned that, at its very best, working with glass is a series of trial, error, and LUCK.