I thought the patch in question might be the tin..
I'm afraid, Watcherinla, we are going to need much bigger images so we can see the whole thing much better.
However, your description of colours coming out everywhere in the light would suggest I'm probably right about silver chloride; any duller metallic bits, I think are the tin.
From your username, are you in the states? Did you find this piece in Austria, or get it from there?