Polished silver has no colour of its own — it is a mirror, and what you read in it is the room. The colour arrives with age. Silver sulfide grows across the surface a few hundred nanometres thick, and light reflecting from the top and the bottom of that film interferes with itself: gold first, then magenta, then blue, in step with how far the tarnish has grown. It settles into the struck recesses, because those are the parts a cloth never reaches, so the mark holds its own history in the places hardest to clean.