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topic 30619

Fade Resistance of Color Anodized Aluminum

Current question and answers:

February 4, 2021

Q. Autoclave failure after hard anodizing?

What would be the reasons of failures in autoclave after hard anodizing?
we found color fading after autoclave in hard anodized parts of 1 Mil thickness. We have done nickel cold seal for 8 minutes at room temperature and 4 minutes of Hot seal at 90 °C.

- Belgaum karnataka india
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February 6, 2021

A. Organic dyes always fade when heated in an autoclave.

robert probert

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

Previous closely related Q&A's starting in:


Q. We manufacture suspension struts/shocks that are fabricated from 6061-T6 aluminum billet and tubing, then color anodized. These are used for off-road racing, hence, they are exposed to a great deal of sunlight. Our customers order a variety of colors, but unfortunately, we have found that not all anodize colors withstand sunlight the same.

With red anodize being our most popular color, and worst for light-fastness, is there any anodize treatment or post application that will help resist fading in sunlight? We are considering to use black anodize exclusively and no longer offer other colors.

Mark Jensen
Suspension Parts Manufacturer - Sharpsburg, Georgia, USA
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simultaneous 2004

A. Different dyes from different manufacturers offer different light-fastness properties. There are probably hundreds of commercially available dyes, two different anodizers would likely not be using the same dye.

We anodize many colors for the same type of parts you are describing with success. Of course all colors (including black) will fade with exposure to UV lighting, over time. A good seal after dye is imperative.

Don't give up because your supplier isn't meeting your requirements, try a different source or contact a dye mfg. and inquire about color light-fastness of their product.

Good Luck,

Bill Grayson
Metal Finishing - San Jose, California


A. The primary dye manufacturing companies rate color fastness of each dye. It would be worth looking into. For my 2 cents worth, I would look at using the two step method of anodize. This actually plates a metal ion into the anodize, so is very color-fast. Some may call it architectural anodizing. Not all colors are available, but there are shades of a great many.

James Watts
- Navarre, Florida


A. Some red dyes are more fade resistant than others, so that may be your first line of attack. I know that US Specialty makes red dyes that go from a rating of 3 (1= poor, 8 = excellent) to 6-7. Their two highest rated dyes are Specialty Deep Red L and Specialty Bordeaux 2R. So you might want to talk you anodizer into using one of those two dyes (or other light fast red dyes) or find one who does. The other thing is that how fast a dye fades is dependent upon how much dye you were able to get into the part; if you start calling out for a thicker anodize you may see a significant improvement. After that, make sure the parts are being sealed properly, preferable in a hot nickel acetate bath - I know that a hot water bath will leach some of the color and it is my understanding that the cooler temp seal baths don't provide as much protection against fading (although I may be wrong on that, we exclusively use hot baths and I'm not familiar with the cool temp set-ups).

Good luck! (By the way - if you have any fasteners that you need red anodized to blend in with the shocks and struts, contact me through the link below.)

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
accurate anodizing banner

March 22, 2011

Q. Sir,

We use sulfuric acid Anodizing in our factory .. our problem is we do coloring for our parts. We follow anodizing by dyeing followed by sealing with Sealofix ZAB. But what's the problem? Our anodized parts are getting faded off within ten days. We use to maintain 18-22° C, DM water for all the rinses maintained within the limits, dyeing time is 10-15 minutes, sealing time is 10-15 minutes.
Suggest your advice on this

Chemist - Anodizing - TAMIL NADU, India
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March 25, 2011

A. Either the anodizing is not thick enough or the seal is not sealing.

robert probert

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

March 28, 2011

A. You fail to mention your seal temp. Use the high end of the allowable for your seal material.

James Watts
- Navarre, Florida

March 15, 2012

Q. Is there a way to test and/or judge within one day whether color anodized parts are going to fade very soon or not?

UV lamp or oven, any recommendations?

Ben Slimani
- Novi Sad, Serbia
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March 18, 2012

Q. We are getting some frames (around 5-15%) of the total production that gets faded on only one side (either the upper part of the frame or the left part of it).we are keeping this frame in a box with cover to prevent it from getting expose to sunlight. what will be the possible cause of this problem and how to prevent it?

Ronald Caya
quality assurance - Mariveles, Bataan, Philippines
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March 20, 2012

Q. We are having some problems on the aluminum frames (6063) that we use on our product. We are encountering some problems that are same with the first posts (or sometimes worse). For example 1-pc frame suddenly fades in color on the left side but retains its color on the other side.

fading on anodized aluminum-1  fading on anodized aluminum-2  fading on anodized aluminum-3  fading on anodized aluminum-4  fading on anodized aluminum-5  fading on anodized aluminum-6  fading on anodized aluminum-7  fading on anodized aluminum-8  fading on anodized aluminum-9  fading on anodized aluminum-10  fading on anodized aluminum-11  fading on anodized aluminum-12  fading on anodized aluminum-13  fading on anodized aluminum-14
Click thumb-size graphics for larger views

Does anyone of you have any possible solutions for this? We will really appreciate it. Thank you all.

Mark Anthony Gomera
manufacturing - Bataan, Philippines
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Color perception relative to thickness, pore size, and cell size

June 25, 2013

Q. Hi,

I recently developed a specification for an anodic coating on aluminum frames (AA-M10C22A44 and it must meet performance standards defined by AAMA 611-12 section 8) but our facility in Asia is complaining that the 18um thickness is not standard there. They are saying that the standard thicknesses are defined by AA10, AA15, and AA20. I suspect 15um is probably okay, but my gut tells me anything less than that is likely to be too thin (this is an architectural application with a 25 year warranty and what I've read indicates maximum erosion rates of 0.5um/year, depending on the environment).

Because this brought up the question of "how thin is too thin a coating" I had to do much more research on the topic and it seems I'm lacking quite a bit of information. It's not apparent how the cell & pore sizes affect the appearance of colors/hues. I would imagine that using process parameters that create large anodic cells and small pore diameters would produce a different apparent color than process parameters that create small anodic cells and large pore diameters (using electrolytic coloring which is deposited at the base of the pore, of course).

Additionally, regarding erosion of the oxide layer, it's not clear to me how a seal would wear relative to the oxide layer. Would it wear slower/faster/similarly to the oxide layer (I'm assuming a nickel acetate seal)? If it would wear faster, what kind of meniscus could I expect with regards to pore size (and hence, how thick the oxide layer would be relative to when the colorant begins to disappear)?

I tried to get a quote for looking at these factors but it doesn't seem like the process has enough control to get coatings only 5um thick for the purposes of approximating the look of a piece after so many years of wear. Is there a university setting that might be more helpful for answering these types of questions?

Thanks so much!

Ben Nielsen
- Newark, Delaware
^-- Answer or Comment on this question --^

A. Hi Ben. I can't offer anything about pore size & cell size, but thickness is crucial -- you can't absorb enough dye without sufficient thickness. If you're doing pastel colored anodizing, a thickness of 0.0002" can be more than enough, but if you want really saturated colors (black being the most saturated) you need greater thicknesses. 0.0004"-0.0005" is very common for parts that will be dyed black, and I've been to shops which insisted on 0.0006" for their black anodizing.

If an individual black anodized part gets insufficient thickness because of bad contact or whatever, you know it right away because the part comes out purple instead of black (the dye is not saturated enough).

In my limited experience 15 microns (.0059") sounds perfect but my experience is with organic dyes, not 2-step or integral color metallic dyes where different thicknesses might be involved.


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Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
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