Tooth enamel is very hard.
enamel paint
A type of paint that dries to a hard, glossy finish; used in art, crafts, and model-making.
I apply enamel paint to the plastic model.
patent leather; enameled leather
Leather with a glossy, mirror-like finish; often used for shoes and bags.
She is wearing patent leather pumps.
I applied enamel paint to the wooden desk.
She's wearing patent leather shoes.
The patent leather on the shoes started to peel.