aluminium would melt if anything before the glass.
when i did enamelling silver foil was often used, gold could be, and sometimes copper embedded in clear vitreous enamel looks a lovely pinkish tone. Avventurina glass has its colour because of the copper filings-
Unless its enclosed in molten glass the foil can detach or rub away.
some foils on beads that look gold are actually silver covered with a transparent amber glass colour. obviously gold is more costly.
thin foil works well with glass because its flexibility allows for the expansion and contraction of hot glass cooling down without adding stress.
try holding strip of kitchen foil to a flame and watch it shrivel away ! (but take precautions not to set your home ablaze, please)
A variety of foils have been used for decorating glass beads. The Venetians have also used an application of gold powder, that produced a somewhat different effect—and may have extended the use of gold, such that less actual metal was required to make a good lustrous appearance. But in most cases the foil or powder was covered by glass which protected it from vaporizing entirely.
Regarding avventurina glass: This is sometime characterized as having resulted from "copper filings being added to the glass." This is a great over-simplification. However the copper was added to the glass, the copper itself was melted into the glass batch. Then the batch was held at the correct temperature for a required length of time, allowing the copper to crystalize—forming avventurina glass. Seen under a microscope, these millions or billions of crystals have the form of perfect tiny pyramids of copper, or as two pyramids fused base-to-base. They are not merely "filings."
In recent years, at Java, where many reproductions of old beads have been made over the previous nearly-30 years, some beadmakers have made versions of gold-sandwich glass and foil beads—and they now use aluminum foil to substitute for silver or gold foil. So it is possible to use aluminum foil to make foil beads. (I was so-informed on my first trip to Java in 2008. And this was reconfirmed by a serious bead importer from Holland a few years later.)
JDA.
I suspect these might be aluminum, because there's no tarnishing on the foil, even on the exposed parts.
Now I don't have to feel bad about using superglue to repair them! :^D
The aventurine copper thing is fascinating! I can't imagine what that looks like under a microscope.... Surreal.
