chemical conversion coating on aluminum cast

[maya04]

hello
we have an alumimum casting (356)
that went through vacuum impregnation and then alodine
after that when wiping the cast with a white cloth we discovered black stains on the cloth.
any one have an idea why?
if we remove the alodine chemically and then coat it again will it harm the impregnation?

 

[swall]

First of all, determine if the Alodine chemistry and impregnation resin are compatable. Also ask the Alodine supplier's tech rep if Alodine before impregnation is recommended or impregnation before Alodine. What reqirements for the casting do you have? Corrosion test, cosmetic evaluation?
At this point, you don't know that the residue on the wiping cloth is even an issue.