Problem Blue Mountain Pottery
There's a stain on this pottery plate that looks like an oil stain. I have tried everything to get it off to no avail. Would anyone know what it might be, or what caused it, or how I can remove it?
It is not a 'raised' stain, but when you look at it against the light it looks like an oil slick.
Any/all opinions of all you resourceful and knowledgeable people welcomed. Thanks.