How do you know when it's time to have a French copper gratin pan re-tinned?
Great question, and I'd like to add a supplemental question: anyone know a good source for re-tinning?
This guy's the expert. His site is under construction, but you can still email him a question. http://www.brooklyncoppercookware.com/
Well when cooking in a copper vessel you must understand that copper can harm you if you cook with it. Thus the tin lining. So if you have spots of bare copper then that is bad. If the spots are small and your not using something very acidic then you should be ok. Acidic foods such as tomatoes or vinegar can leech out material from copper.
I'd like to ask yet another supplemental question: Is it true that I shouldn't subject tinned copper pans to very high temps? And if so, what's the max?
477 degrees is the temp. that tin melts.
I sent a note on Friday to the Brooklyn Copper Cookware site recommended by Merrill and received a response yesterday. My question was: "I have a French copper gratin pan, about thirty years old. I'm not sure whether it needs to be re-tinned. It's looking a bit beaten up, with some very slight, superficial blistering. How do I know when it's time to re-tin it?" Here is some useful information they sent: "What you describe is actually pretty normal for tin linings. The slight blistering you note is a sign that the pan was likely heated empty at some point, but unless the blister has broken through to reveal copper, and then a pretty good-sized patch of exposed copper (about the area of a dime), the pan is perfectly safe to use. The tin itself is safe to use if it's still molecularly stable, meaning it's not cracked or flaking, and even then a few fine flakes of tin are not toxic - one takes in more tin ions daily in the form of stannous fluoride in supermarket toothpaste.
Tin can also wear uniformly over many years such that a very thin veneer is left over a wide area. If you can see the pink/reddish copper color showing through there may be fine fissures exposing copper that are not necessarily visible. It's a good idea to retin in this case as well.
Small amounts of copper can leach into food only under acid conditions.
Acid foods cause exposed copper to oxidize, revealing the characteristic greenish color ("verdigris") associated with weathered copper. In the case of iron the same process yields rust - many metals in pure molecular form bond readily with oxygen to cause corrosion, as do elements and structures elsewhere, such as the cells in our bodies. Foods with so-called "anti-oxidant" properties prevent this.
Getting a bit of copper in one's food is not necessarily dangerous as ions of copper are an important trace nutrient. Too much of it, however, and it becomes a burden to cells of the liver and the oxidized form of copper is toxic in the liver. That's why copper has been lined with tin for cooking for about 7500 years. Pure tin is molecularly stable and non-reactive." ;o)
Antonia, thanks so much for sharing this response with us -- learned so much!
Thanks barry and Antonia!
Retinning? East Coast Tinning in Rhode Island. http://www.eastcoasttinning.com
I am pretty sure that Brooklyn Copper Cookware does retinning as well.
Try Newlyn Tinning for all your copper cookware re-tinning. Newlyn, Cornwall, United Kingdom.