To clarify.

put the jeans (I used a cotton undershirt) into the altoid tin. Close the tin. Put a small hole in top of tin's lid (I used the smallest drill bit I had). Put the entire Altoid tin (with said cotton enclosed) into the fire, I used the BBQ after dinner was finished.

Like someone said, once the smoke comes out the top, take it off. Not all my patches were charred, and some were too charred, but there was a decent amount of "just right" available.