Dezincification is caused by the preferential removal of zinc from brass under corrosive conditions. It is unique to brasses, the alloys of copper and zinc.
Zinc is a relatively reactive metal, second only to magnesium in the galvanic series in terms of least nobility. Even alloyed with copper, the atomic bond between zinc and copper is relatively weak. Under corrosive conditions the zinc is attacked and preferentially removed, leaving behind a porous, copper-rich structure with negligible mechanical strength. White powdery deposits appear on the surface first, but left unchecked the part will ultimately fail.
Dezincification can be prevented by reducing the zinc content of the brass and by adding tin, antimony, arsenic or phosphorus.