Well, one baking question and one icing question.

1. I am baking a chocolate cake and want to double the recipe. The original recipe calls for 2 teaspoons baking powder and 3/4 teaspoon baking soda. Can I double these ingredients or does the ratio of baking powder/baking soda change with different size recipes?

2. As I am making this cake for a child's birthday, I am making the icing with (yuck)crisco/butter and confectioners sugar. I have found that children do not like a real buttercream. However, unlike real buttercream, the crisco/butter/confectioners sugar icing is not shiny. Is there any way to make this icing shiny, such as adding glycerine or corn syrup? Thanks!