Perfect fondant icing flows smoothly but sets with a glossy finish. Too thin and it runs off completely, too thick and it doesn't coat evenly, leaving visible brush marks or lumps. The consistency should coat the back of a spoon but still pour in a steady stream. Temperature affects flow - slightly warm fondant pours better but too hot melts the buttercream underneath. Test on one cake first, adjusting with water or icing sugar as needed. Professional bakers work quickly once the consistency is right as fondant firms up rapidly.