The heat needed for Keum-boo will ideally be between 260 and 370°C. Pure precious metals like gold and silver - those that feature prominently in the original Keum-boo technique - have a remarkably similar atomic structure and, thus, have a great potential for bonding together. Heating the metals to the aforementioned requisite temperature causes an electron exchange between the two metals which creates a permanent diffusion bond. Remarkable, too, is the fact that this fusion bond occurs well below the soldering temperature for either of these metals alone.