Here is a list of substances that may be in your home and will react with copper. Most on the list need to sit on the copper for an extended period of time to produce a color change. This also means that highly visible substances such as tomato sauce will be less likely to have enough time to react as clear substances such as fingerprint oils or water. While these are technically chemical reactions they are not they type that produce vapors or heat so don’t worry.
Found something that reacts in your kitchen? Let us know!