I'm not so much of a baker, but I have made a cake or two in my time, and I can distinctly remember making glazes with icing sugar and fruit juice (eg orange, lemon, etc.)

There is also such a thing as merengue powder, which I believe is used for royal icing. That's hard stuff, if memory serves...

Hope this helps! Maybe Barbara or one of the fine bakers from the baking board will sign in.

cheers!

Carolyn!