The best way to make the backdrop on Art Deco cake?

Jane, you could get black cardboard and cut out the shapes you want. Then, cover one side with the silver foil and get white edible paint to do the designs on the other pieces. When those are all dry, carefully hot glue the pieces onto the cake board (measuring them up next to the cake to make sure they all sit flush with the cake; remove the cake) and let it dry for atleast 24 hours. Good luck.