is it really worth trying to find one with a solid top? Or,
could I just put a piece of cast iron or somesuch on top?
You can use any fairly thick, heavy piece of metal that will hold up
to heat. A bench block, a piece of steel plate, copper plate,
aluminum plate. Ideally, the plate will cover the element entirely.
It can even be done on top of a gas range.
would there be any advantage to using this for other
soldering jobs where even heat distribution is critical?
Well, you could, but you might have a little problem with the heat
rising from under the plate. If you're not careful, you can melt
your hoses. A lot of people wear gloves when doing keum-boo to
prevent getting toasty fingers, and that's with having lots of
nerves telling you things are getting too hot. A better choice will
be a firebrick or a trinket (tabletop) kiln for this purpose.
has anyone tried using any of the oxidizing solutions used to
patinate silver for the oxidation part?
Yes, typical liver-of-sulfur solutions are used most often. The gold
isn't very reactive if no steel is introduced, and stays bright, or
can easily be polished with a light touch. You can look at some of
my pieces in the Orchid Gallery.
I think there are a few other artists there with patinated keum-boo.