Carbon buildup

The black, flaky crust that forms when oil and food residue are repeatedly burnt onto a pan instead of polymerised. It looks like heavy seasoning and behaves like grit.

A pan that is wiped with a thick oil layer after every use builds carbon within a month. The test is a fingernail: seasoning is smooth and slightly glossy, carbon flakes off and feels rough.

Carbon is often mistaken for a well-seasoned pan because both are black. Food sticks to carbon, browns unevenly on it, and flakes of it end up in the food.