Although buttercream frosting and rolled fondant are the preferred decorating medium for most cake decorators, coloured piping gels allow you to create unique cake decorations on your cake, for example, a river. After covering a tiered cake in rolled fondant, use blue and green piping gels to create a river on the cake. Add rocks to the river using edible paints. Even with little decorating experience, you can create a river on your next cake using piping gel.
Prepare three cakes according to recipe instructions or using your favourite store-bought mix in round cake pans: one 9-inch, one 8-inch and one 7-inch. Allow the cake to cool completely before decorating.
Cover all three cakes with a layer of buttercream frosting using an offset spatula.
Roll a 16-inch circle of green fondant 1/2-inch thick. This is thicker than you usually use for fondant, but this allows you to create the river. Place the circle on top of the 9-inch cake. Smooth it on the cake using a fondant smoother. Cut the excess fondant away using a knife.
Roll a 15-inch circle of green fondant. Place it on top of the 8-inch cake and smooth it with the smoother. Cut away the excess fondant.
Roll a 14-inch circle of green fondant. Place it on the final cake and smooth it as before, cutting away the excess fondant, when you are done.
Stack the three cakes on top of one another with the largest on bottom and smallest on top.
Press an offset spatula into the surface of the cake where you want the river to be to create a 1-inch wide and 1/4-inch deep canal. Press the spatula anywhere you want the cake to run, including over the sides of the cake and down the tiers.
Use edible paints to paint rocks inside the canal. Allow the paint to dry for one hour.
Squirt blue piping gel into the canal, on top of the rocks. Spread the gel around to fill the canal. Squirt two wavy lines of green piping gel on top of the blue gel. Swirl the two gels together using a toothpick. Smooth the surface of the river with a paintbrush.
Decorate the remainder of the cake, as desired. Add rocks, trees, bushes and dirt using moulded fondant.