Reply to "My flooding tends to mottle"

If you're using egg whites, I'd recommend adding cream of tartar with your powdered sugar, which stabilizes the egg whites. I used to have that fat-bleed problem often when I used an egg-white based royal icing (instead of meringue powder based). The fat bleed was exacerbated by too thin flood icing and a warm, sunny window. Since I switched to using meringue powder and a thicker flood, I haven't had any problems with fat bleed. Good luck!