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topic 1263

Interference color anodizing of aluminum and two-step (electrolytic) coloring



A discussion started in 1997 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.

(1997)

Q. I'm looking for some people that have experience with "interference color anodising".

Who can help me?

Pierre Raes


(1997)

A. Are you possibly referring to "two step anodizing" of aluminum?

What is the question?

James Watts
- Navarre, Florida


(1997)

A. If you are talking about anodizing aluminum, then most probably you want to know about multicoloring -- a 2-step process of treating freshly anodized parts. We are presently installing an automated line, and one of the processes here is this multicoloring. The process is capable of producing (and reproducing) greys, greens, blues, violets.

Max Stein
captive metal finisher - Montreal, Québec, Canada


October 27, 2012

thumbs up signRegards to Mr. Max Stein. I'm sure he was my manager when I worked with CP Tech in Montreal, Quebec.

Dado Macapagal
- Ont., Canada


(1997)

A. Both processes exist, a one step and a two step electrocoloring on aluminum. Both processes produce "interference colors".

Guillermo Luna
- Mexico City, Mexico


INTERFERENCE COLORING OF ANODIZED ALUMINUM

(1997)

A. Interference coloring of anodized aluminum has been introduced to the market since 1984. It is a process which is different from the conventional 2-step electrolytic coloring process. The color effect is due to the interference of visible wavelengths rather than light scattering. Interference colouring is by either a 2-step or 3-step process. There are basically two methods for interference coloring :

"2-Step Interference Process": This is a new process.The conventional anodizing bath and Sn-electrocoloring bath are used. But, a different power supply and close control of anodizing parameters is required. The function of the power supply is to widen the pores of the anodic film (This is called modification of the film). Anodizing solution temperature is maintained between 17.2 and 17.8 °C., sulphuric acid concentration between 175 and 200 gpl. The power supply for anodizing is a DC-and-AC device with current density controller. Normal anodizing is done to get the required film thickness and then the interference (modification) step is performed in the same tank. Thus anodized load is then colored in a tin-based electrolytic process.

Anodizing and Coloring of Aluminum Alloys

"3-Step Interference Process": This process requires a second anodizing process in a phosphoric acid solution to widen the pores of the normal anodic film obtained in the first sulphuric acid anodizing bath. The first anodizing bath is conventional sulphuric acid solution, temperature controlled at +/- 0.5 °C, concentration controlled at +/- 5 gpl. In the second anodizing tank, a special power supply and phosphoric acid based solution is used to modify the pores of the anodic film. Thus anodized load is then coloured in tin-based coloring electrolyte to have bluish grey, blue and green colors.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


(1997)

A. S. Kawai & M. Yamamuro's article, entitled "Interference Coloring of Dual-Anodized Films on Aluminum Containing Electrolytically Deposited Thin Metal Layers" and published in Plating & Surface Finishing in 1997, may interest you.

Ling Hao
- Grand Rapids, Michigan


thumbs up signThanks for updating us on this technology, Timur and Ling.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


sidebar July 27, 2014

Q. Who can help me download the S. Kawai & M. Yamamuro article, entitled "Interference Coloring of Dual-Anodized Films on Aluminum Containing Electrolytically Deposited Thin Metal Layers" and published in Plating & Surface Finishing in 1997?

Thank you,

zhang dou
aluminum anodic - china zhejiang


July 2014

A. Hello Zhang. You can join NMFRC.org at a cost of $40 and view this and other Plating & Surface Finishing copyrighted articles. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



(1998)

Q. We are experimenting with a Sandoz 2-step electrolytic black process for medical purposes. We also have a request for other colors using this type of colorfast process. What is the latest on this? Is a process commercially available? Does it work, and is it fairly easy to do? Who would be a good reference contact on this?

Thanks,

P Faxon


(1998)

A. Clariant (Sandoz) and Henkel Surface Technologies (Novamax) both have 2-step electrolytic dyeing processes. Both work well and I think both are developing alternate colors. We (Albright-Wilson) have a process which produces red based on copper salts which is in use at a customer in MN. 2-step tanks are generally easy to control and the finish looks great.

Lee Branch
Richmond, Virginia


(1998)

A. Would you consider 2-step coloring by electrolytic process instead of dying? By electrocolouring you can have colors from light bronze to black with a Ni, Sn or Co solution. There is also a new concept named "interference colouring" which has two different methods, giving colours blue and gray.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


(2001) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sirs or Madam:

We are beginners in electrolytic colouring. We do not know what chemicals we could use to colour our profile aluminum bar by electrolytic method, - we also need to know the uses and where to get them. Please teach us your knowledge.

Thank you!

Le Viet Dzung
- ThanhMieu Ward, VietTri City, PhuTho Province, Vietnam



sidebar (1999)

Q. I am looking to start anodizing paintball markers, parts, air tanks, and other small items. I need help on finding the right process. I'm no scientist. I have no idea where to begin. Please help. Thanks, Dana (Ms. Lucky)

Dana Herman
paintball

probert book
Aluminum How-To

by Robert Probert
$89 New
The Chromating - Anodizing - Hardcoating Handbook

A. Hi, Dana. We've been discussing electrolytic coloring of anodized aluminum here, which is used for architectural applications because of its stability -- but most anodized aluminum items (including paintball guns) are actually dyed with organic dyes. You clean the aluminum, perhaps lightly etch it, desmut it, anodize it (most commonly in 10% by volume sulfuric acid), dye it by immersion in an organic dye tank, and seal the dye in by boiling or, better, with a low temperature sealer.

A good place to start might be to access a copy of "Aluminum How-To" =>
or the Metal Finishing Guidebook (which would introduce you to technologies & suppliers), or to retain an anodizing consultant [link is to finishing.com Consultants Directory]. Best of luck.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Electrolytic coloring with copper vs. tin electrolytes

Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

(2002)

Q. Cu vs. Sn for electrolytic coloring of anodized aluminum?

There are several electrolytes to color anodized aluminium. Today most widely used one is the tin-based methods. In the older days Nickel and Cobalt based methods were also popular. I also know copper-based method is also possible to color anodized aluminium in maroon and black and this is a cheaper method. But, I doubt the ultraviolet resistance of Cu-based colors in outdoor exposure. Is there any paper or other information about the durability of the anodized colors obtained by Cu-based method compared to that of Tin-based one?

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


A. Hi Timur. You are probably aware that "The Surface Treatment and Finishing of Aluminum and Its Alloys" has a 53-page chapter on electrolytic coloring, comparing the nickel, cobalt, tin, and copper electrolytes, and that perhaps the most basic reason for electrolytic coloring is UV resistance. I made the perhaps mistaken assumption that all of these electrolytic coloring methods are completely UV resistant, but Table 110 (5th edition) says copper electrolytes can exhibit dulling of the surface, while pages 635-636 summarize 3 studies on the subject of the lightfastness of electrolytic inorganic coloring. For my own education, is there a mechanism by which UV radiation can alter any of these inorganic finishes? Thanks.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Can nickel sulphate be added to tin based electrolytic coloring solutions?

March 26, 2012

Q. Hello Sir,
I'm an Architectural aluminium Anodiser. I am in this field not a long time. During anodising process sometimes, in reduction of coloring salt in electrolyte coloring bath, I cannot match perfect color ... there is need of adding Tin Sulfate. So my question is can I add Nickel Sulfate instead of Tin Sulfate in coloring bath?

My coloring bath is made of
1- Tin sulfate
2- Sulphuric Acid and
3- Stabiliser

Please Sir Guide me. Thanks.

Gohil Manoj
anodize - Surat, Gujrat, India


April 4, 2012

A. Architectural anodising is a little out of my field, but I would be surprised if you could replace tin sulphate with nickel sulphate. Why do you want to substitute one with the other? Is there a tin sulphate supply issue?

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom


April 11, 2012

Q. Yes, supply is issue.
And also lowering plant running cost!

gohil manoj [returning]
anodize - surat gujrat India


July 31, 2012

A. Hello Mr. Manoj ... hope you are fine.
I read your question and comments.
I can help you: yes, you are right, you can add nickel sulfate into tin-based electro-coloring solution.
By adding nickel sulfate you can earn two major benefits:
1. low cost of nickel sulfate because when nickel sulfate is added, then you can do color process with 8-10 g/l of tin sulfate instead of 12-15 g/l
2. you can get more red and shine in coloring of aluminium profile.
I'll come to India after Eid; so if you say, then I'll feel happiness.
Best regards.

Azeem khan
anodizer - karachi pakistan

----
Ed. note: Apologies, but this forum does not put readers into personal contact with each other. If they are willing to share their knowledge and technology freely, please publicly share it here -- we have all the room in the world; whereas, if someone offers consulting or licensing services, they should advertise here because the forum is only possible courtesy of the advertisers. Thanks for your understanding.



September 27, 2012

Q. Hi,

We are trying to install and connect an AC power unit to a tank containing lead^tin salt in order to make a 2-step electrolytic anodise (1st anodizing step is running already).

What are counter electrodes made of? Size?

Bath capacity 1000 L.

Cheers

Sanad Hassan
- New Zealand

October 6, 2012

A. Hi Hassan,

Not sure what you mean by lead^tin. This text editor wont even allow me to reproduce the precise format. So, I'll answer the question as though it was simply "tin".

Counter electrodes are usually 316 stainless steel. The useful area should be a large as possible and a least the area of the work load. By "useful", I mean that the general good practice of keeping counter electrodes (and anodes) slightly shorter and less wide than the work load should be followed. Failure to follow this rule, while increasing the area, has an adverse effect current distribution.

harry_parkes
Harry Parkes
- Birmingham, UK

----
Ed. note: Sorry for the confusion, Harry. Hassan mistakenly wrote "lead", which he asked be changed to "tin". Thanks for answering "as though it was simply tin", because it was :-)


December 27, 2012

Q. Dear sir,
I would like to know about stabilizer used in anodising -- its purpose with tin sulphate and contents used in stabilizer

Mitesh Bhayani
- Mumbai, India


January 10, 2013

A. Hi,
Sorry for the delay in replying.

The stabilizer performs two roles.

1) To lessen the rate of oxidation of tin II to tin VI. in the bath.

2) To act as an oxygen scavenger at the work piece. This increases significantly the rate and depth of coloring.

harry_parkes
Harry Parkes
- Birmingham, UK



March 15, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,
Can you tell me about the analysis for the stabilizer in coloring over the anodized part and what is the function of the above said?

manu sharma
- solan h.p. india


June 2014

A. Hi, Mitesh; hi, Manu. Per Wernick, Pinner and Sheasby the contents can be materials aromatic carboxylic acids, cresol sulphonic acid, thiomalic acid, pyrogallol, resourcinol, and ferrous salts. In view of the many possibilities and the fact that they tend to be proprietary, your options seem to be to either buy them or do a lot of detailed readings of the literature followed by extensive experimentation. Best of luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Fluoride accidentally added to electrocoloring bath

December 11, 2013

Q. Hi,
Salam to all of you :)
Dear friends, I want some help from you, I am an anodizer. By mistake, a worker put 2 kg hydrogen fluoride in tin-based electrocoloring bath solution.
I don't find any problem until now, fluoride was put in 60 hours ago.
Now I want to know that what will be the effect (if any)?
I have 14000 liters of solution in the bath.
Thanks :)

Azeem Khan
- Pakistan



June 26, 2014

Q. G'day,
I'm looking for some advice on how to use the Munk IF30 interference colouring controller.
So it goes that I have a Munk controlled anode tank with:

180 g/l sulphuric acid
8 g/l aluminium
Temp range of 16 to 23 °C
With a Munk IF30 controller for interference

Then I have a Munk controlled electro colouring bath with the following:

Stannous sulphate 22.2 g/l
Sulphuric acid 42.4 g/l
Stabiliser 35 g/l

I am running a 30m2 load and need a dark grey colour

Richard Williams
- Sydney Australia


sidebar July 5, 2014

Q. Dear Sir,
Please provide us the ELECTROLYTIC METHOD FOR MANUFACTURING OF TIN(II)SULFATE, which is used in Aluminium Anodizing process to color development.
Thanking You.

Rajeev Rane
- Pune, Maharashtra & INDIA


July 2014

A. Hi Rajeev. This site focuses only on metal finishing, not the bulk manufacturing of commodity chemicals. But if you are unable to purchase tin(II) sulfate and only need small amounts for an experiment, it sounds like it's as easy as adding tin powder to copper sulphate =>

I understand that it is also possible to add sulphuric acid to tin metal to make it, but that probably introduces some issues of stannic ions. Sorry, my background is only metal finishing and I'm personally unfamiliar with your electrolytic method for manufacturing it. Have you done a patent search? Simply pasting your capitalized phrase into Google or Bing seems to reveal a great deal of detail on the process.

Luck and Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 11, 2015

Q. Hi,

I am currently producing the interference colouring using nickel sulphamate solution. I am doing 2 stage anodising, sulphuric acid anodising and then phosphoric anodising for pore modification.

Does anyone knows how to do the pore modification in the sulphuric acid tank (so all in the same tank), rather than doing the phosphoric acid pore modification?

Mani Govindan
Anodising - Uxbridge, Middlesex, UK



June 22, 2016

Q. Dear All,
What is the difference between 2 and 3 step interference coloring as to aim, cost, advantages/disadvantages, applicability as practical, etc? Could you share with us?

alaattin tuna
engineer - turkey, sakarya


June 2016

A. Hello Alaattin. We appended your question to a thread where Timur Ulucak explained the basic difference. Hopefully other readers will flesh out the answer in the way that you request.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



Formula for bronze colour salt, their stabilizer and sealing for anodising of aluminium

June 16, 2017

Q. What is the detail procedure for making bronze colour salt, their stabilizer and cold sealing used for anodising of aluminium.

navnit kakade
- pune, Maharashtra, india


June 2017

A. Hi Navnit,
In addition to carefully reviewing this thread, which contains a lot of information for you, please try a literature search at surfacequery.com, and also see if Werner, Pinnick, & Sheasby helps you.

Sorry, but we can't print answers to your question except from people well known to us, or references to PUBLISHED references like those I mentioned. Most chemistry of this nature is proprietary, the result of long & expensive development, and there is no practical way for us to know that strangers acquired their knowledge through personal R&D, versus whether we would be facilitating the crowd-sourcing of industrial espionage. But again, if anyone wants to point you to published answers, that's fine.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



Electrocoloring: Stannous sulphate in liquid vs. powder form

August 18, 2017

Q. We at present are using Stannous sulphate in salt (i.e., Powder) form in our electro colour bath. The problem we face is a lot of powder deposition is found especially in hollow sections and inside surfaces. How can it be reduced? Should we start using Stannous Sulphate in liquid form (i.e., stannous sulphate manufactured directly thru electrolysis process)?

Bhavishya Pandya
- Vadodara, India



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