Sometimes you get stuff on your copper that just won’t come off, and you have to get serious.
This copper pot had a price sticker on it when it was new. Whoever used it for the first time peeled the sticker off but left some of the sticky adhesive behind.
When the pot heated up, the adhesive cooked into a layer of super-hard black stuff that’s very difficult to get off.
If I had a polishing wheel, I could probably rub it off, but I don’t. Here’s another look at it. The adhesive has polymerized — it’s turned into a very thin layer like strong plastic.
I did some research and learned that the next level of cleaning this off is to use strong chemicals and a strong mechanical abrasive. I decided to run a little test.
For the chemicals, I would try acetone and naphtha. These are strong solvents but still available at a hardware store. For the mechanical abrasive, I would use steel wool: 000 grade for the scrubbing, and then 0000 grade, which is finer, to help smooth over the scratches afterwards.
I taped over half the area and went at the first half of the stain with naphtha and steel wool. (If you try this, please go outside and wear rubber gloves, as naphtha and acetone emit strong fumes.)
The naphtha did a pretty good job but it took me a good solid 10 minutes of persistent scrubbing with the steel wool. Note the very fine scratch marks — impossible to avoid with this process, which necessarily takes off the top layer of copper.
I then finished the second half with acetone and steel wool. I don’t see any difference in the results between acetone and naphtha — they both did a good job with the polymerized adhesive. Furthermore, they didn’t damage the copper.
For the last step I used the 0000 steel wool to try to smooth out the tiny scratches.
I’m pretty happy with the results. It could use a good professional polish (and retinning for that matter) but I think it looks lovely. My advice to you is that either acetone or naphtha can help remove polymerized oils from copper — but it’s still a lot of work!