I think the oxidation is inherent only in the earlier pieces, while the technique was still being perfected.
No harm in repeating here the snippet of info I have permission to tell folk about, regarding this foiling at Isle of Wight Studio Glass.
Michael Harris invented a special vacuum marver for putting the foil onto the glass.
The surface of the marver has little holes in it, a gentle vacuum is created by passing air under it. The very delicate sheets of precious metal foil are laid carefully on it and the mild vacuum holds them flat, while the gather of glass is rolled over to pick it up.