I'm reorganizing my casting area. Most of my cast boolits look normal but there is one batch of large 45-70 boolits that developed a super fine coating of 'dust'. It is so fine that if I rub the boolit it is like a coating of silver paint. I don't think it is lead oxide as the boolits are still like-new shinny but whatever it may be it is fine enough to where I'm concerned over toxic contamination. I could probably blow hard and send the fine dust flying.
What could this be?