Washing berries is important, but wet berries make frosting soggy. Using berries that are completely dry when you begin decorating ensures that the final decorated cake will look as good as it tastes. Refrigerate the berries before washing them to help the water run off quickly from surfaces that have firmed up in the cold temperature. After washing the berries, gently blot them with paper towels, spread them out in a single layer, and give them a few hours to dry.

Raspberries and blueberries lend themselves easily to a Fourth of July flag cake. Use a modern flag design for a rectangular sheet cake, with the raspberries forming the red stripes between white icing and the blueberries forming the field of stars in one corner.

Geometric designs include concentric circles of raspberries and blueberries, or stripes and lines of varying widths -- some just a single berry wide and others with multiple berries forming thick lines. Create a starburst pattern by forming a star shape with one color of berry, outlining it with the other color of berry, and then adding another outline with the first berry. Sprinkle bright lemon zest over the berries for bits of additional color and flavor.

Even a hodgepodge arrangement of berries strewn over the top of a cake looks gorgeous if you give the berries a shiny coat. Use caramel or honey for a ready-made glaze lightly drizzled over the berries, or mix powdered sugar with lemon juice, maple syrup, fruit-flavored liqueurs or raspberry jam to make your own thick glaze. To add a sugary sheen to the berries, brush them with egg whites, sprinkle them with coarse sanding sugar, and let them dry at least four hours before placing them on the cake.