I just did a google search on the subject of copper annealing, and I
found this article.

http://www.evergreengardenworks.com/copperwi.htm

I can say that I used to rebuild motorcycle engines, and most of them
had solid copper head gaskets. I would anneal them by heating to red
hot and then dropping in a water bucket. They seemed to be much softer
afterward and did not leak so I guess that is a proper way to do it
(whatever works, right?). According to the article, you can use either
method, but he recommends water quenchung to minimize oxidation.

Regards,
Bruce Cunningham
N30464 C177A