Dirt collar or grease collar is seen in -
1.Punctured wound by sharp weapon
3.Firearm entry wound
Grease collar or dirt collar is seen at firearm entry wound.
It is a black colored ring lining the entrance wound on the skin.
It is produced by removal of substances from the bullet as it passes through the skin, that is, bullet lubrication, gun oil from the interior of the barrel, lead from the surface of the bullet, barrel debris, etc.