Take some clay and make a snake shape, or two or three, wrap them up together. Now you should have one multicolored snake shape. Take a chunk (depending on the size of the marble) and roll it up in a ball. Then bake the clay. I took pictures to show how, step by step:

1. Get some oven bake clay.

Oven Bake Clay

2. Roll out two or three pieces into snake shapes.

Roll out Clay

3. Twist the pieces together.

Twisted Ropes of Clay

4. Roll the twisted rope of clay into one snake.

Multi Colored Snake of Clay

5. Break into chunks and roll into marbel sized balls.

A Ball of Clay

6. Bake clay according to the directions on the package, and then let it cool.

Finished Marbles

7. You are now ready for a game of Ringer!