A method of holding the parts of an object together with or without the aid of an adhesive such as an epoxy or a glue. Composite materials such as fiber-reinforced plastics require strong interfacial bonding between the reinforcement and the matrix. In the case of atomic or optical contact bonding, interatomic forces hold the parts together. In optical contact bonding, surface flatness and cleanliness between the mating parts determine the bonding strength, and the atoms at the surface provide the necessary forces. The number of valence electrons in the atoms of a material determines the bonding strength between the group of atoms which constitutes a molecule. In these cases the term chemical bonding is used.