I have a large tin-lined copper stock pot that I got a month or so ago. I have used it a few times to boil a chicken or to make stock, and the tin turned the expected blue-gray color. This week, I made a large batch of chicken soup that had a substantial amount of lemon juice in it. There are now white spots all over the inside of the pot. The tin is dark, with what looks like dozens of little white oxidation spots all over the inside. They have a very slight texture to them--if I slide my finger over a spot, I can feel that it is not as smooth as the other tin, but it does not wash off or scrape off (with a thumbnail).
Does anyone know what this is? Is it a problem? Should I do anything about it?