Clay Rainbow Cake

With a pasta machine or rolling tool, roll out the colored balls of clay to ⅛" (3 mm) thick.
Use a larger circle cutter to cut circles from the clay.
TIP Don’t have a pasta machine? No problem! Try using playing cards or index cards. Grab two piles of cards, place a rubber band around each of them, and then roll out your clay between the two stacks to create an even thickness.
Roll out a thin sheet of white clay to about one-quarter the thickness of the colored discs. Cut circles from the white clay, and place one on top of the purple disc. Then place the blue on top of the white disc, like a sandwich.
Continue placing layers of white clay between the colors to form a rainbow, ending with the red layer on top.
Using a straight cutting blade, cut the cake in half.
Cut the remaining pieces until you have formed 6 equal slices. 
With a pointed detail tool or sewing pin, stir up the colored layers (except for the white) using small, circular motions. Clean the tool between each layer.
Continue texturing all of the layers. Bake the slices for about 5 to 10 minutes at the temperature indicated on the package of clay.
While you bake the cakes, prepare the frosting using equal parts white clay and liquid clay.
Mix with a flat tool until all the lumps are gone and you’ve formed a thick, sticky frosting.
Apply the frosting to the tops and sides of the cake slices
To make sprinkles, roll out a small snake of each color of clay, making each very thin. Bake the snakes for 5 minutes at the temperature indicated on the package of clay.
With a blade, cut “sprinkles” from the clay. Make them as small as possible while maintaining their circular shape.
Make about 10 to 15 sprinkles of each color.
Place the sprinkles on the tops and lower sides of the cakes.
Bake the cakes for another 5 to 10 minutes, and they’re done! TIP Make your cake a charm by inserting a headpin!