Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
Even though it is hard to see I suspect it is melted alum from a pop or beer can. I sometimes find these out in the water too and they sound like gold with that low growl in the headphones.