Chemical Reactions in Fused Glass

I had the opportunity to participate in a class at Delphi Glass in East Lansing, Michigan last summer.  My  interest in understanding the chemical reactions resulting in the interaction of some glass and some metals has increased as I work more with fused glass.

Roy, the teacher, was very knowledgeable and shared a lot of information in a relatively short class.  Over the next few days I will share some of the interesting things I learned and provide an example or two.

Below is a three-layer stack ready to fuse.  On the bottom is blue streaker glass, which is somewhat opaque and NOT solid blue, but marbled with a lighter tone of blue.  On top of that is a piece of heavy copper foil, and topped with a narrow piece of clear 90 COE glass.  Notice that neither piece of copper is completely covered by clear glass.

Copper foil on blue glass with partial clear cap before entering the kiln.

Below is the same piece of three-layer glass/copper/glass after it has been fired.  Notice that the copper covered by clear glass has oxidized to a burgundy-red, but the exposed edges, not covered by the clear glass, look much more charred and have little burgundy-red color.  Also notice that the marbling in the blue glass is more pronounced.  I do not believe the characteristics in the blue glass are related to a reaction to the copper.  The rounding of the corners of the glass is a characteristic property of fluids when the are able to move - for glass this means heating.  The property creating the rounded corners is "surface tension."  All fluids will try to occupy the least space possible - think of a soap bubble.  Surface tensions pulls the surface molecules together as much as possible for the environment they are in.  In the case of a soap bubble, they create a sphere.  In the glass below, contact with the firing paper and gravity interfere with the formation of a sphere.......gravity wins!

Copper foil on blue glass with partial clear cap after leaving the kiln.