In a large mixing bowl combine flour, salt, and alum. Mix well. Add water. Mix well and shape dough in a ball. Knead dough on a lightly floured surface for about 5 minutes until smooth. If dough is too stiff, sprinkle with water. If too moist, add flour. Work with small portions at a time. Store excess dough in an airtight container. Form shapes as desired using a cookie cutter or braiding length of dough into dandy canes, wreaths, or other holiday symbols. Microwave 5-10 minutes depending on microwave strength.