As an alternative to painting, the powder is electrostaticlly applied to the cage usually made of cold rolled steel. When applied the cage is then heated to a temperature of about 400 F degrees. The process is more environmentally sound than painting. The coating usually results in a safe protective coating for the cage. There are several principle suppliers of powder coatings.
Formulas differ by manufacturer.
Most contain no zinc. Zinc can be incorporated into the formula in one of three ways. First the zinc oxide can be used as a pigment especially for white colors. Zinc can also be added for corrosion resistance. Neither of these are thought to be a factor in pet bird cages.