Thanks in advance to anyone who can help us with this mystery. Here's the story:
Two of us live in Orange County CA and both of us have had a situation in which the copper leaf mixed into our polymer clay has turned black. The specifics:
I live 4 miles from the ocean, the other person lives about 12 miles inland, maybe more.
Her pieces turned after they were cured and glazed. Mine turned when the clay was still raw.
Her pieces turned just a few days after they were made. My raw clay sat out for almost a month before it turned.
Her work surface was a ceramic tile (no sulphur involved). Mine sat on a flexible green quilter's mat made by Ofray and there might be some rubber (with sulphur) involved.
Neither of us have had this problem with our silver leaf.
The weather during the last four weeks has fluctuated a little bit (which is relative for Southern Californa) but the most notable event is slightly higher heat and humidity due to hurricane and tropical storm influences from the Gulf.
None of the clayers in our forum, some of whom live in much wetter and/or warmer areas, have reported a similar experience. We are not necessarily using the same brand of leaf. She got hers from Fire Mountain Gems and I got mine from Michael's - it's the brand with the picture of The Madonna on the front.
So, given all these different factors, does anyone have any "hit the nail on the head" thoughts as to what is happening?