I have handled, washed and sold hundreds of these beads and these are my thoughts. The true old vulcanite beads only come in black and because of their age are fragile and break easily. The newer brightly colored beads are vinyl. I'm not sure if they are so dirty because they've been used or because they are soiled to appear old. I've been told that Nigerians wear them for ceremonies but I do not know which tribe/tribes. I continue to sell them as vulcanite because that is what people search for when looking for them on the Internet. I have no evidence to verify these thoughts and appreciate your tests and information Rosanna.