Getting ready to ship my Christmas cookies, and I always stock up on pretty containers for them way in advance. I got a bunch of great old tins with the coolest pictures on them at a local barn sale, but now I see a few of them have black stuff all over the bottoms and I don't want to gross anyone out. So far it doesn't wash off, with soap or silver polish, has anyone ever had any luck? If not, no biggie, I have enough for now, and I think I paid only around 50 cents each. But they're really cute.