Many of the optics we make are gold coated via electron beam
evaporation. Most of the evaporated gold does not make it onto the
optic but onto the walls of the chamber which I scrape off. It is then
slightly contaminated for me to use so I have accumulated several
ounces of nearly pure gold that I simply keep.
Gold is actually cheap compared to some things. I had to do some
Rhodium coatings and it is about 10X as expensive as gold. As I write,
I am doing Platinum coatings as an experiment.
I've considered gold coating some stainless fittings on my boat as a
joke as it would cost me nothing and I think it would stick due to the
Cr in the SS. However, pure gold is so soft it scratches just by
looking at it.