The scoop! (verified by several sites. so it's the grind not the sift! from "What's Cooking America"
powdered sugar Also called confectioners sugar. In Britain it is called icing sugar and in France sucre glace. It is granulated sugar ground to a powder, sifted, and a small amount (3%) cornstarch has been added to prevent caking. The fineness to which the granulated sugar is ground determines the family X: factor: The X: designations are derived from the mesh sizes of the screens used to separate powdered sugar into various sizes. Thus, 4X would have a larger particle size, whereas 10X would have a smaller particle size.14 X is finer than 12X, and so on down through 10X, 8X, 6X, and 4X (the coarsest powdered sugar). Confectioners or powdered sugar, available at supermarkets, is usually 10X. Always sift it before using.
have to get some 14x -- interesting to see how smooth a frosting that would make.