Blotchy overdye

[bomscho]

A lot of things were working fine been hinky lately.

Been working with a lot of pieces that I realize are cut from the same alloy of sheet. My process has been

Cut (plasma cut)
Shape + deburr
Polish
Ano
Dye
(Redye)
Seal in nickel acetate

When they're dyed the first time, they look beautiful, uniform, perfect. When they're masked or acidwashed, though, the first color is fine - but the second becomes blotchy, and more so with every bleach/sulfuric dip + redye. Eventually with each treatment it stops dying at all; usually by the third bleach/acid/redye it'll take only the lightest shade of the third color, in blotches.

Here is a piece that was dyed yellow, masked in parts, then redyed brown. The other was dyed blue, masked, dyed violet, masked, and dyed green (this is the backside, the flip with the masking was more uniform in green but several shades lighter -). The effect could be desirable but is NOT what I'm looking for here.

Many thanks..

[spankey666]

when you acid dip them after bleaching, how long are you dipping, how strong is your acid ? are you dipping in bi-carb before re-dying ?

[bomscho]

Same I've been using for months, per acidrain's recipe: full strength bleach, one part water to 3 acid I think (made it a while back).


I used to dunk/rinse for 20 seconds maybe, then dunk/rinse 10-20 seconds in acid. I've experimented with as little as 5 and as much as 1 min in each now..results still quite poor.

[bomscho]

Another thing: both of these pieces, and others with the same problem, are cut from *the same* piece of sheet aluminum. I haven't anodized any other material over past 2 weeks. Could it be the alloy -- has anyone seen an alloy do this?

[spankey666]

i have had big issues recently with machined plate. HE30 grade. bad anodising, and a strong linear grain pattern in finish, even the machined surfaces. a very hard and brittle finish, but also very matt and dull and blotchy. for weeks ive been battling, fresh everything, trying to work out what was wrong, then did some turned aloy same grade, perfect everytime. so the issue was with the plate and not my technique. the parts were for the Buell factory race team, so needed to look good, i have to re-cnc new plates with a different sheet of plate too see how it works out. you will be suprised how often we get a bad batch of unworkable / poor machinable alu.

[bomscho]

Hm, yeah...you're probably right. This is from a scrapyard, was thick sheet used for punches, definitely AL but who knows what alloy.

Wouldn't you have liked to know that HE30 should be avoided?! Maybe we need a sticky thread on alloys and alloy issues (what do I know?). I almost never know what alloy I'm working with.

I didn't think we needed to know metallurgy to do this, beyond using 6061 or 6063 for cathodes if we use AL.

Going to try same things with different stock, but this time with coupons first. Boring.

Thanks!

[acidrain]

Those blotches do not look like alloy problems, especially since the first color comes out good.
I suspect handling issues.
Are you only handling by the wires?
Are you always following the bleach with acid?
Are you rinsing well (both spray and dunk)?

[bomscho]

Those blotches do not look like alloy problems, especially since the first color comes out good.
I suspect handling issues.
Are you only handling by the wires?
Are you always following the bleach with acid?
Are you rinsing well (both spray and dunk)?

I follow your technique as explained on this forum nearly to the letter.

Definitely only wire handling, always. Always bleach, rinse, acid, rinse. Only standing time is if masking is involved and that's 20 min for rubber cement to dry. Using the same source of rinse water as out of the ano tank.

[spankey666]

and following acid dip with bi-carb dip ?

HE30 is 6082 so should ano well, but the 8x4 sheet we bought doesnt

[spankey666]

also when i acid dip after bleaching, its just a for a second or so, just enough time to give it a quick slosh then straight into bicarb to neautralize, then rinse and re-dye.