The pure form of gold used in dentistry is known as:
Cohesive gold
For cold-welding, gold should have a clean surface free from impurities. Gold attracts gases, e.g., oxygen to its surface and any absorbed gas film prevents cohesion of individual increments of gold during their compaction. The manufacturer, therefore, supplies the gold essentially free of surface contaminants.This type of gold is known as cohesive gold foil.
Ref: Mannapallil basic dental materials 3 ed page no 114
Cohesive gold
Noncohesive gold
Class I casting gold
Class IV casting gold