This is probably one of the coolest art forms in jewelry.  Adapted from the Japanese style of sword making in the early 1600's, Mokume Gane takes on a whole different look.  Basically, it is a process of layering different metals such as White Gold and Silver or White, Yellow and Rose gold. The metals are layered alternatively one then the other in a stack.  this is then heated to a point at which they do not melt into a blob, but enough to firmly adhere to one another.   Not to go on too much with the gory details, the jeweler will then go through a process of rolling and twisting the billet (stack they created) in order to get the really super cool designs.  The pattern will vary depending on how the jeweler cuts the metal at this point.   As you can see in the pictures, once the metals are to this point, the jeweler really has an amazing pallet to work with and everything is left to their creative abilities.  Set a stone in it, accent it with cool designs, whatever your hearts desires.  It is truly one of the neatest jewelry styles.