Rainbow dust is also known as edible glitter. It is used to create pictures and decorations on cakes, cupcakes, cookies, popcorn, candy and other food items. Rainbow dust is made by combining gum arabic or hardened sap with water, then infusing it with color. The dust adds a subtle, sweet flavor to foods. Rainbow dust comes in a wide variety of colors and is easy to apply to any food. There are several ways to apply the dust to a cake.
Frost your cake with the desired icing. Sprinkle rainbow dust onto the icing while it is still damp and fresh so the dust will stick. Use a large salt shaker to shake the dust over the cake.
Apply rainbow dust after icing has set by adding 2 to 3 tsp. of rainbow dust to 1/4 cup edible glue or confectioner's glaze. Paint the dust onto the cake with a small paintbrush.
Mix rainbow dust with the icing before you frost the cake if you would rather have the glitter mixed in. Add 2 to 3 tsp. of rainbow dust to a small tub of frosting. Mix well with a spoon, and frost your cake.