Black Dye looks blue or grey

[cesgirl]

Looking for help with anodizing with the black die. We have the whole caswell kit and have been sucessful in the past but are currently having problems with the black dye only.

The shop guys have been using trial and error for now, but i'm trying to get them to use the 720 rule. here is a break down of what we just ran...

polished aluminum piece surface roughly 8.8insq
degreased and then de oxidized
anodized at 70 degrees, for 60minutes, set at .4 amp
-when placed in electolytes immediately went to 13.5, by about 10 minutes it peaked at 15.8 and then by 60 minutes was down to about 15.4
then placed in color for 15 minutes (ph for color is at 5.6)
of course we wash between each step with water
when the part came out of the dye it was like a dark grey before they were coming out a steel blue (before we corrected the ph)

we are looking for a polished jet black finish...can anyone help?

thanks so much

[destroyer125]

Try annodizing for 20-30 minutes longer then normal time for Black dye....Ive had this problem before and It was because of pore size

[acidrain]

Yes, what desroyer said.
I've found if you calculate from the 720 rule, and shoot for a 1mil thickness, the black will dye nicely.
You were running a little more than 6 amps per sq. ft.
At 6 apsf, a 2 hour run time would calc. out to 1mil.

[cesgirl]

thanks for the replies....

We ran it for 84 minutes last night and it came out great....
I believe we achieved a .7mil anything under that just didn't come out jet black....

that 720 rule is right on the money!