When making gumpaste calla lillies, I usually make my centers first and put them on toothpicks to dry. It is easier to work with them when they are hard. If you'd like you can roll them in cornmeal or yellow sugar. You would need to put gum glue on the centers first so that the cornmeal/sugar would stick. Then using a heart shape cutter you would cut your petals out. The size of your centers would depend on the size of your petals. Hope this info helps. Good Luck!