I love this technique for cookie decorating.
It is very important to make royal icing the right consistency.
My recipe for royal icing...
1 egg white
3 cups powdered sugar
3-5 drops of lemon juice
1 / 4 teaspoon cream of tartar
almond extract if desired
While rubbing egg white, gradually add sugar (do not beat egg whites). At the end put cream of tartar, lemon juice and essence. Consistency should not be too thick, but not liquid.