Hi, I have a Presto pressure cooker from about 1952 that I believe is aluminum. I've had it for over a year, and use it all the time as a pot, only once as a pressure cooker. I hand wash it with liquid dish soap, but when I go to use it next, I find it covered with a coarse white powder-like substance. This has only been happening for a few weeks. If the pot is sitting in a skillet, there is a ring of it there, too. Nothing else in the cabinet has this. Has anyone else had this problem? Could it be the aluminum breaking down? Is it still safe to use, and will it still hold a seal if I use it as a pressure cooker? Thanks in advance for any help.