Hello I use tartaric acid on my royal it makes it really nice.
Try it and let me know. THe amount about 1 tsp to 3 cups of royal icing.
No cream of tartar is something else, (I think) Tartaric acid is what they use on sour sweets is a very tangy powder it makes the royal icing taste tangy, not so sweet and it dries it quicker when use to decorate.
Is that the class recipe? 3 tbsp meringue powder 1lb confectioners sugar and 5-6 tbsp water?
Did you know that tartaric acid is an alph-hydroxy acid and is used in anti-wrinkle creams? You can google Tartaric acid and read more about it. When I was in beauty school, we started making our own creams for skin care and this one really worked. The only way that we could get ahold of Tartaric acid was to go to a chemical company for it. I wonder if we could substitute citric acid for the tartaric? Tartaric is a derivative from wine making. It comes from the grapes.