Is there a process that will stop copper from turning dark after it
has been sprayed with polyurethane? If the copper is polished with
something like Brasso then washed and sprayed it still tend to darken
in crevices?
Bill Lockett
You might give Incralac a try. This coating is made specifically for
copper allows, has UV inhibitors and can give protection outside for
up to 15 years and if it needs to be remove (because of
discoloration) there is a remover that can be user to remove the old
application so a new one can go on without hurting the underlying
material (patina for sculpture).
John Dach
Be certain your copper is completely dry, not just apparently dry,
before you coat it.
Many(most) clear coatings are not anywhere near impermeable to water
or oxygen. Polyurethanes for sealing wood are not designed to be
totally impermeable. Look for coatings specifically designed for use
on sealing metals like Nikolas lacquers or Incralac.
James Binnion
James Binnion Metal Arts