This composition, usually in a ratio of 5 parts potassium nitrate, to 3 parts aluminum powder, to 2 parts sulfur, is especially popular with hobbyists. It is not very quick-burning unless exceptionally fine ingredients are used. Although it incorporates sulfur, it is in fact fairly stable, sustaining multiple hits from a hammer onto a hard surface. Adding 2% of its weight with boric acid is reputed to significantly increase stability and shelf life, through resistance to dampening through ambient humidity. Other ratios such as 6 KNO3/3 Al/2 S and 5 KNO3/2 Al/3 S also exist and work. All ratios have similar burn times and strength, although 5 KNO3/3 Al/2 S seems to be dominant.