I just took a mixed metals class this last weekend. The gentleman
who taught the class, Jima Abbott uses the technique you
mentioned. He completes his piece, polishes it and before he sets
the stones he takes an torch oxy-propane or oxy-acetylene with a
bushy flame and lightly goes over the copper and brings out the
color. He goes over it for a short time and then lets the piece
cool and then goes over the piece again repeating the process
until he gets the colors he wants. He said you can take it too
far and you can never determine what the results may be. He said
he never has put anything on his pieces to keep the color on them.
He has being doing this for thirty years and has repeat customers
and he said that he has seen some of his pieces that are 15 years
old that still hold the color. I hope this is useful information
for you and what you are looking for.
Willits, Northern California
"Shoot for the moon. Even if you miss it you will land among the stars."