I have been doing alterations for many year but yesterday I was taking the hem out of a Winter coat and found in the whole width of the hem a black powder that looked like gun powder. I was up at the hall with friends and they agreed with me. So they suggested I call the police to check out the substance. I didn't have my phone with me so one of the ladies called. They came and said it was probably some rotted thin rubber that is sometimes put in garments and not to be alarmed. Has anyone ever run into this. I have seen a clear thin elastic used in garments but never heard of it ever rotting.