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  for Metal Finishing since 1989
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Black dye problems

I am having trouble with my black dye. Last week our analysis came back as being too low in concentration. The suggested add from our lab was 18 pounds. After the add was made, the dye started coming out with a light grayish green look. Has anyone ever came across this problem before? Any suggestions would help

Randy A. Mattson
- Seattle, Washington
2002

What brand of dye are you using?

Dado Macapagal
- Toronto, Ont
2002

Sandol Deep Black MLW powder. Well I decided to go ahead and dump the tank and make up a new one. When I had it dumped, I found that when our maintenance group installed the airlines, they anchored it down with an aluminum block. I'm thinking that was why we were having so much trouble.

Randy A. Mattson
- Seattle, Washington
2002

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Sounds like it could be the prob.. but normally Sandoz' metal dept will also tell you the al concentration with their analysis was it within parameters?

Marc Green
anodizer - Boise, Idaho
2002

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MLW can come out greenish and/or purplish on some alloys particularly if the anodic film is not thick enough. So if you are "anodizing by amps" as some of the later writers are pushing these days, perhaps you had the "effective surface" area mis-figured and did not get enough thickness. Or perhaps if you are "anodizing by volts" you did not have the proper voltage that is recommended for the particular alloy. Or perhaps the alloy changed, without your knowledge, from 15 volt alloy to a 21 volt alloy, in which case if you continued to use 15 volts you would not get thickness and then the dye shade would be different.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2002