I've been playing around with a technique called Mokume Gane. Now my very basic understanding of this technique is that it originated with those who made swords for the Samurai's in Japan. Basically the belted sheets of different metal together before making the blade. The process left patterns created by the different coloured metals. Should you wish to correct me on this, go right ahead. ;-)

Basically the process with the clay is multiple layers of coloured clay with a sheet of silver foil between each. Smoosh whatever you can lay your hands on into the stacked sheets and viola! Lufley patterns to play with.