A small percent of boric acid is recommended to deter a spontaneous reaction between the nitrate and the zinc. A slight variation in the composition will produce Penny stars. Method Grind each chemical, separately, as fine as possible with a ball mill, mortar and pestle or a coffee grinder. Screen the chemicals together by passing the mixture several times through a mesh screen. The function of the dextrin is to act as adhesive and bind the composition together, eventually hardening it into a solid mass once it is dry. When preparing the stars, use a solution of about 75% water and 25% isopropyl alcohol, with no less than 75% water. The alcohol helps the charcoal absorb the potassium nitrate solution by reducing water's surface tension, thereby allowing the solution to enter more of the charcoal's pores. The drying time of the composition is also reduced, as alcohol evaporates faster than water. Add some of the solution to the composition and mix well. The Granite mix can now be rolled, pumped, pressed etc. Keep adding until it is damp enough to clump together if you squeezed an amount in your hand. Dry slowly, no direct sun to avoid cracking from uneven shrinkage.