This is a short explanation for the above mentioned workpiece. If you want to create a workpiece by yourself please follow the step-by-step instructions under courses (navigation to the left).
This creation has been made out of Fimo and Creall-therm. Both kinds of clay can be intermixed.
First I have made a marble structure out of green and white clay (take a look at Basics).
 The polystyrene foam ball was directly covered with this layer. The ball will then shrink in the oven when heated. If you cover the form first with tin foil you keep the form intact. This is not the way as you want to be able to extract the ball after baking your workpiece. 
 The partly covered form is put on a thick layer of green/white clay as seen on the picture. Be sure to have the right thickness, it has to support ball and babies lateron. This creation will now be put into the oven for about 30 minutes.
Meanwhile I have modelled the babies.
After the cooling process the babies are put into the workpiece. The whole creation has to be baked again for 30 minutes (110 degrees C).

For more information on how to model with polymer clay: fimo-frutsels