Cut four 6-inch lengths of nylon thread and tie one end of each to a 1/4-inch nut. These will hang from the dowel rod into the bread pan, so the threads need to be evenly spaced. Your first thread should be tied 1 3/4 inches from the end of the dowel. Allow the thread just enough length so the nut dangles freely just above the pan's bottom when the dowel is resting on the top edge of the pan. Each of the remaining threads should be attached to the dowel 1 1/2 inches apart.
Heat 3 cups of water in a sauce pan. When the water starts to steam, lower the heat and gradually stir in the alum until you can't dissolve any more.
Pour your warm alum solution into the bread pan. Place the dowel so it rests from end to end on the top edge of the bread pan. The 1/4-inch nuts should be dangling in the solution.
Let the solution set for 12 hours. This amount of time will vary according to the type of crystal being formed. Alum crystals grow rapidly, so 12 hours is a relatively short amount of time. The objective here is to form quality seed crystals on the threads, so with subsequent trials, adjust your timing so you have a good formation of 1/32-inch crystals.
Remove your threads from the liquid. If you can't see any crystals on the threads, let them dry out before reinsertion in the solution. Most likely, the threads have crystals too small to see, and this will help stimulate further growth. If you do see a nice accumulation of tiny crystals, gently pinch them with your fingers to break away the weaker ones. Take great care in doing this because you want to keep just three or four of the best crystals on each thread while getting rid of the rest. The few crystals remaining will serve as seed crystals for growing larger ones. When only three or four remain on each thread, slide them so they are evenly spaced.
Wash the thread between your seed crystals with warm water. Microscopic crystals most likely have formed here, and these will stimulate unwanted crystal growth. Be very careful to wash just the threads without washing away your larger seed crystals.
Reinsert the threads in the solution to continue growing your crystals. Prepare more solution, if necessary, as the seed crystals must remain submerged. Periodically wash away any newcomers. The secret to quality crystals is starting with quality seeds. The amount of time required depends on the type of substance used. However, even with fast-growing crystals from alum, it can take weeks to grow a large one.