English: A lot of lower-quality paper (e.g. newspaper or cardboard) is acidic, which means it will damage whatever it comes in contact with, and consume itself over time.

Here is an example of an artifact held in a cardboard box – the acid from cardboard inflicted damage on the schematic. The solution is to use acid-free cardboard and paper.

Also, human sweat is acidic and etches itself in metal, for example (although it’s only visible after a few months) – and that’s why you are supposed to wear gloves whenever interacting with exhibits... and generally avoid that if possible.