a. When several alloys are processed with the same conversion chemical, color may vary from alloy to alloy.
b. Due to the high level of impurities and oxidation on the surfaces of aluminum welds and castings, color may not be as uniform as that obtained by treating wrought alloys.
c. Dark spots may result from dripping or rundown of the conversion chemicals when the parts are lifted out of the treatment tank. A small amount of spotting does not result in coating degradation but must be minimized by quickly rinsing the parts after treatment, and use of proper racking techniques.