Cohesion of gold foil is an example of:

Pure gold is the noblest of all dental metals, rarely tarnishing or corroding in the oral cavity. It is inactive chemically, and it is not affected by air, heat, moisture, or most solvents. At room temperature, two thin sheets of atomically clean pure gold can be welded under  pressure. The  procedure  is  also called cold welding because it is conducted at room temperature. Ref: Phillips 12 ed page no 413