Useful coffee stains

Stamp Cups
As someone who is trying to make it in the world as a potter, I try to make nice pots and be confident that that will sell them. Sometimes I try to figure out some sort of clever quirk that might push someone over the edge to actually buy a piece- a nice detail that shows that I paid attention - something to show that it was handmade. This stamp cup idea is definitely not an innovation that I have thought about before, and I don't actually think that I would make something with this idea.... but at least I can appreciate the cleverness.