Take some cheap peanut oil and rub on the piece you wish to be
brown. ... When you think about it, it is the oils in our skin that
causes the pennies to turn brown. I also found by doing successive
coatings it gave different browns.
Sort of. The oxidation of the pennies isn't from oil in the skin, but
rather the salts, plus moisture (like perspiration...)
The peanut oil finish is one I first saw experimented with at
Cranbrook in the 70s. Then, we'd spray it on while gently heating
with a big annealing torch. It was, at the time, inspired by
japanese metal finishes. But I digress... What is browning with the
peanut oil is not the metal. It's the oil itself oxidizing and
solidifying to a sort of varnish-like surface coating. That's why
successive coats give a darker color. You can think of this a little
bit like what happens with a well cured wok. The steel hasn't turned
that nice dark color that indicates a well seasoned surface, (which
if you've used one, is almost as non-stick as a teflon pan, so long
as there is also a trace of oil there again in cooking.) It's the
repeatedly oxidized and built up layers of the cooking oil you're
looking at. In the peanut oil finish, the tricky part is to get it
even. That's why Agnes learned, and is passing on, the need to rub it
off, which leaves an even thickness thin film. If the oil layer is
thinner and thicker in various places, then the color won't be even.
Multiple thin layers work better, are more durable, and look better,
than fewer thicker applications.