OK, here is a little from my experience:
Of the spray clear coats in cans that are out there these two are
recommended - Incralac and Permalac. Real coatings made specifically
for this purpose. Sherwin Williams also has a two part spray that is
excellent. I'll see if I can get that name.
Now, products like this two part and high quality laquers require
some effort. A spray booth, compressor and airbrush for sure. The
key is the very fine spray provided by the air brush. Purchase a
quart of the absolute best clear laquer you can find. Spend the
money! This is important. Prepare a bunch of pieces for finishing.
Suspend them from fine wire in the spray booth. Then cut the lacquer
you will need in half with fresh thinner. It will look like water.
Apply it with the air brush in very thin coats. The idea is to just
mist the piece and let it dry. Then mist again. The water thin
laquer will be absorbed by the oxide, not just coat it. That will
seal it. How many coats? Two or three at least. Suit yourself.
Keep your air brush and spray booth absolutely immaculately clean.
The first time a glob squirts out or dust is kicked up by the
compressed air you will regret any skimping.
Another choice is powder coating. This I only know a little about,
but, it is a choice. There are very clear powder coats available.
They can be applied thin. They are baked on and harder then heck. It
can be done at home with a toaster oven or you can find a local
powder coater for help.
Good luck, Bill
Reactive Metals Studio, Inc.
PO Box 890 * Clarkdale, AZ 86324
Ph-928/634-3434 * Ph-800/876-3434 * Fax-928/634-6734