Powdered realgar is orange-red in color and produced by the sublimation of arsenopyrite or crushing the native red crystals. Generally, mixtures employing realgar are sensitive to both shock and friction but sensitivity varies with different oxidizers. Many old-fashioned formulas included this as a component in various star compositions, for producing yellow smokes and noise units (together with potassium chlorate). While the small modern sound units are generally produced using the oxides of lead, copper or bismuth, it´s sometimes difficult to find replacements for star-making. We do not suggest that you come to rely on this for any formulas that you want to make on a regular basis. It is very poisonous,
Note that in some formulations realgar and orpiment are listed as equivalent alternatives.
Realgar can very easily cause cancer. In the long run, it’s more poisonous than white arsenic. Realgar is a sulfur compound and will explode when mixed with chlorates. It is an arsenic compound and highly poisonous. The resulting ash from burned pyro compositions is likely to contain water-soluble arsenic oxide, which is considerably more toxic than either of the sulfides.