Seems like every bike on CL has a patina.

https://www.google.com/webhp?sourcei...20bik%20patina

What is a patina, anyway, and how do I know if my bike has one?
Is it in the crank, or the headset, or somewhere else?
Can I put an aftermarket patina on a bike that didn't come with one from the factory?
Does Oval Concepts make one?