dibutyl phthalate, dinitrotoluene (toxic and carcinogenic), akardite (asymmetrical diphenyl urea), ortho-Tolyl urethane, and polyester adipate. Camphor was formerly used but is now obsolete. Stabilizers prevent or slow down self-decomposition. These include diphenylamine, petroleum jelly, calcium carbonate, magnesium oxide, sodium bicarbonate, and beta-Naphthol methyl ether Obsolete stabilizers include amyl alcohol and aniline. Decoppering additives hinder the buildup of copper residues from the gun barrel rifling. These include tin metal and compounds (e.g., tin dioxide), and bismuth metal and compounds (e.g., bismuth trioxide, bismuth subcarbonate, bismuth nitrate, bismuth antimonide); the bismuth compounds are favored as copper dissolves in molten bismuth, forming brittle and easily removable alloy. Lead foil and lead compounds have been phased out due to toxicity. Wear reduction materials including wax, talc and titanium dioxide are added to lower the wear of the gun barrel liners. Large guns use polyurethane jackets over the powder bags. Other additives include ethyl acetate (a solvent for manufacture of spherical powder), rosin (a surfactant to hold the grain shape of spherical powder) and graphite (a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity). Flash reduction Flash reducers dim muzzle flash, the light emitted in the vicinity of the muzzle by the hot propellant gases and the chemical reactions that follow as the gases mix with the surrounding air. Before projectiles exit, a slight pre-flash may occur from gases leaking past the projectiles. Following muzzle exit, the heat of gases is usually sufficient to emit visible radiation: the primary flash. The gases expand but as they pass through the Mach disc, they are re-compressed to produce an intermediate flash. Hot, combustible gases (e.g. hydrogen and carbon-monoxide) may follow when they mix with oxygen in the surrounding air to produce the secondary flash, the brightest. The secondary flash does not usually occur with small arms. Nitrocellulose contains insufficient oxygen to completely oxidize its carbon and hydrogen. The oxygen deficit is increased by addition of graphite and organic stabilizers. Products of combustion within the gun barrel include flammable gasses like hydrogen and carbon monoxide. At high temperature, these flammable gasses will ignite when turbulently mixed with atmospheric oxygen beyond the muzzle of the gun. During night engagements, the flash produced by ignition can reveal the location of the gun to enemy forces and cause temporary night-blindness among the gun crew by photo-bleaching visual purple. Flash suppressors are commonly used