Try soaking it is Calgon water. I used it years ago when I ruined my baby's diapers with clorox in hard water. It turned them so rusty, they looked like you had cleaned rusty iron pipes with them. I soaked them over night in cold water with Calgon in it and they came out white as snow. I used Calgon for years since then. It is a water softener but removes stains also. Good luck.
sassy granny