Roseann,
I work in copper and have used heat coloring for years. I have not,
however found a satifactory sealer that retains the brilliant
color. I have tried waxes, a wide variety of lacquers and clear
sealants. It seemed as if every sealant reacted with the copper and
changed or dulled the color. The sealants that reacted the least
with the copper were water-based polyurethanes, if I remember
correctly. The difficulties I had with sealants have discouraged me
from using them on my work, especially if I want to retain the
brilliant fushia and blue.
Dianne