I’ve done a fair bit of it on silver. Given what I thought I knew
about how it worked, I wouldn’t have expected it to work easily on
copper (because of the surface oxides) and not at all on steel.
My thought was always that it was low temp diffusion bonding, with
the pressure of the burnisher serving to add enough energy to kick
it over the activation energy hump.
In reading your paper, you propose oxygen transport through the gold
film. OK, but what then about the oxygen bonded to the surface atoms
as oxide? Especially on copper or steel? (nevermind that Al always
has an oxide skin.) You have to do something to reduce those oxides,
and simple pressure isn’t going to do it. Most puzzling.
As a suggestion to make burnishing easier, gold and steel will gall
on each other, so I stopped using steel burnishers in favor of
either agate or pyrex burnishers. They work much better, and there’s
no tendency for the gold to stick or gall.
Pyrex burnishers are child’s play to make with most standard
jeweler’s torches. Pick up some pyrex rod, and you can have a
burnisher ready to roll in under 5 minutes.
(I can shoot you a PDF if you need. It’s easy, and they work great
for normal burnishing as well, at least on silver and gold.)