When exposed to the atmosphere, brass tends to form a protective tarnish film that impedes corrosion beyond a few micrometers into the metal surface. The tarnish will deepen in color from bronze to dark brown, and may eventually take on the green color of a patina in some environments. The important point is that brass's corrosion rate in normal atmospheric conditions is low and self-limiting, and the corrosion products that do form are not objectionable. In addition to atmospheric corrosion resistance, brass also withstands exposure to a wide range of water compositions, including automotive coolant solutions. Brass is generally inert to organic liquids and gases, although it should not be used in mineral acids or acid salts.
Alkaline salts are less objectionable.
Brass is susceptible to three types of corrosion. These include stress-corrosion cracking, which can arise in ammoniacal environments, amines, mercury compounds and nitrite solutions. Brasses are perhaps the least susceptible copper alloys to sulfide pitting. Also, road salt solutions contaminated with sulfide-laden exhaust emissions do not appear to affect brass. Brass can, immersed in acidic and mildly basic waters, corrode by dezincification, but this also has not been a problem in automotive applications.