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Electrocolouring of anodized aluminum: speckles & white powder stains

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January 24, 2022

Q. Paulo here from Brazil. Trying to locate what is causing these stains in eletrocolouring. Similar to gas trapping, these stains are appearing in every color we currently produce. The shape of the stains is similar to dripping.

56407-1a   56407-1b  

We have noticed that our tin bus bar is showing an extremely accelerated deterioration.

Paulo Sérgio
- Santa Catarina, Brazil

Closely related Q&A's, oldest first:


Q. I anodize aluminium profiles in my plant. We have 2 problems that I'm hoping someone will have come across before:

1) How does one effectively drain hollow profiles which get filled up with sulphuric acid? We tilt the jig manually and wait for the sulphuric acid to pour out which is decidedly clunky.

2) During the electrocoloring process I find that small bubbles form on the profiles at immersion time which prevent proper coloring. To work around this we lower the profiles in the electrocoloring bath, then raise the profiles and slowly let the solution pour off. We then dip the profiles into the electrocoloring bath and start the process. We find that the first dip prevents any bubble formation. Again, this seems a clunky solution.

Clues anyone?


Sanjay A. Bulchandani
- Bombay, India


A. Sanjay:

1). You can drain hollow profiles by tilting the jig manually and waiting for the sulphuric acid to pour out. It is decidedly clunky :-)

I don't know if there is any other way, but some shops invest the time in careful jigging with poly shields and so on to steer the stream neatly back into the tank.

2). In nickel plating, where clingy hydrogen bubbles are a nuisance that cause gas pits, wetting agents like sodium lauryl sulfate (baby shampoo) are used. I don't know whether such additions would have an ill effect on your electrocoloring.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


A. Sanjay,

I assume your aluminum profiles are over 3000 mm long and you transport them by a crane, possibly a "bridge crane". I could recommend :

  1. Rack the profiles inclined so that the two ends will have about 100 mm difference
  2. After taking the load out of the bath, incline the crane so that the solution drips down. Wait about a couple of minutes (provided the load not dried) and then move the load next stage.

Those will help you in two problems you asked.


Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


Q. Hi,
We have produced some Bright Gold Sections of 6060 alloy anodised in sulphuric acid to 5um and then cold sealed.
after the gold electrocolor treatment the profile has fine speckling that is of natural color. The pitting looks similar to pitting produced when brightening (phosbright 171)is conducted using low nitric concentrations. I can not find any literature that describes process defects for gold electrocoloring, what would possible causes be?


Rodney Gutsell
Anodiser - Australia


A. First get the thickness up to 10 or 15 microns. If that does not solve the problem, then come back and we will explore some other problems.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


Q. Hi again, we've noticed white stain and purple hue on electrocolored anodized bars. the bars are packed in PE low density packages and left for more than 4 months in this package. Any information on the source of such defect and how to overcome it ? and which type of package would be useful for packaging.

Elie Kattar
consumer - Jounieh, Lebanon


A. Low density PE can contain low molecular weight polymer which tends to be greasy.
Anodised surfaces are absorbent, even when sealed. This could be the cause of your problem.
I would always recommend wrapping in acid free tissue paper first then possibly craft paper for protection depending on how the parts are to be stored or transported.

geoff smith
Geoff Smith
Hampshire, England


Q. Thank you Mr. Smith.....but paper packages (cellulose) are sensitive to moisture and water and could develop sticky surface and damage more the surface ... I'm actually looking in enhancing the PE properties buy using additives that can reduce the iridescent phenomena (anti-fog, less colorant, ...) or use medium or high density PE if possible ... any information on that issue could be helpful thanks.

Elie Kattar [returning]
- Jounieh, Lebanon


A. Elie
If moisture is a problem, I would do for acid free tissue to protect the metal surface and PE bag to keep the moisture out.
I would discuss the type of PE with the bag supplier or better the manufacturer. Most PE bags are for low tech use and they may not understand that you need a quality controlled product.

geoff smith
Geoff Smith
Hampshire, England

December 25, 2010

Q. I am anodizer from Riyadh K.S.A. we have two electrocolouring tanks working, and white powder deposits on processed material irrespective of light/dark colours.we have 5 micron cartridge filters with a filtration capacity of 25 cubic mtr/hr.our filtration works round the clock.can you please suggest how to eliminate this white powder. Thanks

Masood Khan
anodizer since 10 yrs. - Riyadh K.S.A.

June 5, 2021

Q. Hi sir,
we encountered the same problem. Have you corrected it already? Can you give me some advice?

Dhazel De Mesa
- Manila Philippines

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