STAGE 1:
INDUCTION is when normal oxidation takes place, normally
producing the dark brown copper oxide film which can be a
protective barrier against future pollutants. The actual film
composition is dependent upon the type and concentration of
pollutants in the atmosphere, upon the duration of exposure,
and upon the relative degree and duration of wetness on the
surface. High concentrations of sulfides in the atmosphere
can dramatically alter the result of stage 1, producing less
protective, even potentially damaging films. The rate of
oxidation can also have an effect on long term durability of
the surface finish; oxides formed over longer time periods
seem much more resistant to deterioration.
STAGE 2:
THE CONVERSION OF THE TOPMOST METALLIC SURFACE TO COPPER
SULFATE normally begins to occur on surfaces with the most
severe exposure, such as horizontal surfaces. Oxygen
deprivation and deposition of particulates and moisture create
a catalytic situation where electrolytic reactions occur.
(This is the same principle as a battery, where the charged
ions move from a positive to a negative pole.) The visual
symptom of this phase is the formation of thin, light green
patches on the more exposed areas.
