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topic 4422

Aluminum Anodizing Color Match Problems


(2000)

Q. I need to know if 5052 aluminum will anodize the same shade of black as 6262 and 6061? I found out the hard way that 2024 will not.

Ed Miklavcic Jr.
- carol stream, Illinois


(2000)

A. Well let's do a little check on the material compositions first:

Composition: 5052-H32

Al 97.3

Cr 0.15 - 0.35

Cu Max 0.1

Fe Max 0.4

Mg 2.2 - 2.8

Mn Max 0.1

Si Max 0.25

Zn Max 0.1

Composition: 6061-T651

Al 98

Cr 0.04 - 0.35

Cu 0.15 - 0.4

Fe Max 0.7

Mg 0.8 - 1.2

Mn Max 0.15

Si 0.4 - 0.8

Ti Max 0.15

Zn Max 0.25


You have some definite differences in the makeup of the 2 materials, noticing that 5052 has more Mg I'd expect more of a grayish shade out of the material than I would from a 6061, other than that there isn't anything overly striking to me that would tell me that they would color any differently. My best suggestion to you would be to take a 1 sq. ft panel of each and have them processed. As much as we the people might be able to predict this and/or predict that, results don't lie (well most of the time at least :p)

I know I've processed both of these materials, but unfortunately not at the same time, so my data would essentially be worthless to you. I've done 5052/6061 in clear anodize, but not at the same time, so well how can I compare when I don't have 1:1.

Matthew Stiltner
plating company - Toledo, Ohio


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

(2000)

A. They do not etch the same or anodize the same. Metal from different lots or tempers will not look exactly the same. Boils down to how close does it have to be. Start point is certainly the test recommended by Matthew.

James Watts
- Navarre, Florida


(2000)

A. We are an architectural anodizer and one of our primary concerns at all times is color uniformity. I agree with James Watts when he says that "metal from different lots ... will not look exactly the same." We have found that buying aluminum for anodizing is like buying bolts of cloth from a tailor for making clothes. If you want color uniformity you must start with a single lot of aluminum, or consecutive lots of aluminum. By "lot", I mean the coil or coils made from a single ingot that was originally rolled into sheet, or the billet that pushed into an extrusion.

Notice also in Matthew Stiltner's post that there is variance in the alloying constituents. (Max means the content could fall all the way to zero.) Even for a given alloy/temper, you will still have some variance lot-to-lot in not only mechanical properties, but also chemical composition as well.

I hope that helps.

Penn

Penn McClatchey
Southern Aluminum Finishing Co - Atlanta, Georgia
supporting advertiser


(2000)

A. Hello everyone,

I'm going to chime back in here on this topic. These two guys provided a lot of helpful information and when necessary corrected some of my mental errors. I wanted to basically remark on Penn's comments about the quality of aluminum and its makeup from lot to lot. This is so true, and I have spoke with a gentleman in great detail about this issue. He basically stated that most material available to a majority of us is for the most part lacking in quality from lot to lot. That the mixtures even noticeable from the same coil can be different and vary throughout that coil itself. He said that the mixtures are (I may have these backwards now, I've got a cold and my brain isn't working at its full 100%) homogeneous not heterogeneous, meaning of course that they are improperly mixed throughout the material, where you might have .04% copper at one end of the coil and at the other end have .035% copper, now this is a small minute difference in my opinion, but generally this will probably not be the only difference in the makeup/mixture.

Also, now this may be an opinionated response, but this person I spoke with also stated that material from Germany/Europe regions and also from Japan was of extremely high quality and highly praised for this reason.

Best of Luck to Everyone, and keep on putting in your 2 cents, its well appreciated here I know and I like to see what others have to say about so many issues.

Matthew Stiltner
plating company - Toledo, Ohio


(2000)

A. If you think about it, the aluminum in an anodized part is the finisher's most important raw material. Yet the anodizer has little information and no control over its alloy composition, heat history, hot/cold working, grain structure, intermetallics, surface finish, uniformity, inclusions and contamination. All of these things affect the conversion process and can result in non-uniform anodic coatings; within a single part, part to part, and run to run. Matt stated that a copper difference of .035% to .04% within a coil was minute. I would suggest that that depends how you look at it. In absolute terms, he is correct, i.e., .040-.035 = .005% difference. In relative terms .... (.040-.035)/.035 = 15% difference. Anyone trying to manufacture a consistent product would have to look at raw material variations of 15% as significant.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
supporting advertiser
Wadsworth, Ohio

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



Anodizing: coloring problem

(2001)

Q. Aluminium anodizing for decorative purpose --

1. Why is it so difficult to get the color right from anodizing? The limit range for color is so large that when the two parts are assembled together we can see a big difference - aesthetically no good.

2. Why is it silver color is easier to match then other colors, e.g., blue, red?

Wong Weng Fei
- Penang, Malaysia


(2001)

A. Whole skyscrapers are built of anodized aluminum, so color matching is not an insurmountable problem. But etching, anodizing, dyeing, and sealing can all affect the color. The dyes will appear darker and more saturated if the anodizing is thicker, which is why you may have less consistency problems with the natural silvery color.

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


(2001)

A. In silver anodizing you control the surface texture obtained by mechanical or chemical treatment (satin or bright) and anodizing conditions (composition, temperature, current density and time). In dyeing anodized film, besides the variables above you have to control colouring solution composition, temperature and time as well. More parameters to control more difficult to get the same appearance.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey



Fixing anodized aluminum color problems

(2002)

Q. I had some parts anodized. They were supposed to be a satin or matte black. However they came back to me a deep purple color that is almost black but when placed near something gray or black the purple really shows. This is not acceptable to my customers.

At this point I need to have this problem fixed. The company that performed the anodizing is recommending a black epoxy paint to fix it. I am a bit wary of this as other parts (steel & aluminum) will be clamped to the epoxy painted parts and I am worried that they will crack or flake. I am also worried about changes in dimension, conversion of the finish from satin to gloss, etc. The parts do not have to be black but could be anything from 80% grey to black.

What are my options at this point?

Eric Brooks
- Oneonta, New York


simultaneous (2002)

A. The problem could be fixed by stripping the parts & redoing them properly.

David A. Kraft
- Long Island City, New York


(2002)

A. They should not be a purple black. Some thing in the anodizer's system is out of "balance". If his suggestion is paint rather than rework, I would ask for my money back and ship them to an another anodizer for strip and re-anodize (that will promise a black black). You will have some loss of material and the surface will be somewhat rougher. Stripping will be an extra cost, but so is painting or remanufacturing.

James Watts
- Navarre, Florida


(2002)

A. Anodizing dye aren't truly black--they are either very very dark red or very very dark blue. However, a purplish color usually indicates that the anodizing wasn't thick enough to absorb enough dye to give a full deep black color.

So for future parts the best approach may be to require thicker anodizing. 0.0005 inches or more is not at all excessive for black parts, even 0.001 inches is not unheard of.

What to do for THESE parts though is a tough one. It's very hard for someone at a distance to tell you whether epoxy paint is a good fix or a shoddy one for the particular instance. A lacquer of a translucent gray tint might be the best compromise between how it looks as delivered and how it will look if chipped.

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


(2002)

A. The anodic coating was not thick enough to absorb all of the blended ingredients of the particular black dye. In the case of thin coatings the blue ingredients of the blend are preferentially absorbed showing purple.

You have three choices: (1) Anodize to a thicker coating like 0.8 mil, (2) Use a dye that will strike at 0.4 mil, I cannot list commercial products on this program. (3) Change anodizing job shops.

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

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como




Acceptable Color Variation on Anodized Aluminum Products

April 12, 2010

Q. I am an owner's representative on a condominium project in Brooklyn, NY. We have received a delivery of anodized aluminum panels (1/8" thick) approx. 3' x 3' that has what we believe to be severe color variation. Are there any standards that we can refer to that can show us what are acceptable color variation for these panels?

Sam Proviser
owner's representative - Brooklyn, New York


April 16, 2010

A. Hi Sam,
I don't think that there any such standards in the UK and I suspect that the same is true of the US.

It is a really fraught subject. Phrases such as "to be agreed between customer and supplier" and "agreed samples" tend to be used in specifications. Perceived color is so dependent on type of surface finish as well as amount of colorant absorbed. I remember being involved is a dispute over anodised and dyed roofing panels. Adjacent panels could look very different even though the anodiser claimed that they were well matched when produced. On this occasion the problem was that the panels had been had been fitted without regard to the direction of rolling (it never occurred to the installer that this was relevant). The effect was like that of a grass lawn mowed in different directions!
Of course, your problem may be simply that it is bad anodising/dyeing.

Harry

harry_parkes
Harry Parkes
- Birmingham, UK


April 18, 2010

A. Color variation on "architectural anodize" should be controllable and less dramatic than with conventional anodizing. There are specific anodizing firms that specialize in just that type of anodizing - they do entire skyscrapers that use large sheets, millions of square feet, of color anodize with little variation. Typically those sheets are quite large - 20-foot to 30-foot long in many cases. Your 3-foot square sheets I'm guessing were done by a conventional anodizing job shop who have less expertise. You might want to contact someone like Keymark in Fonda, NY, who is one anodizing firm that specializes in "architectural" applications. You may have gotten your small sheets done cheap, but your results reflect just that!

milt stevenson jr.
Milt Stevenson, Jr.
Anoplate Corporation
supporting advertiser 
Syracuse, New York

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August 12, 2013

Q. Dear Sir,
I use chemical coloring in automatic line to color into gold anodized aluminum parts (chemically polished). The process is carried out correctly, but the parts from the lower rack are darker than those from the top. The rack length = 1 meter, and the coloring time = 45 seconds. The lower part enters and leaves the bath in additional time of 5 +5 seconds. What can be the problem?
Is the coloring bath too strong, or too fast?

I would really appreciate your help.

Karolina Potocka
- Bydgoszcz, Poland



Variations in Anodising color

July 9, 2014

Q. When anodising is done on certain sections, the color is not uniform. There are different longitudinal shades as in the picture enclosed. Why does this happen? How to correct his problem?

4422

Siddharth C
- Belgaum, Karnataka, India


July 10, 2014

A. My first thought is it appears to be an inadequate rinsing issue, this especially appears to be the case on the bottom part in the picture. Are the parts racked horizontally, or vertically? If horizontally, is the discoloration always on the top, or the bottom? If vertically, is the discoloration on the inside, or the outside?

Every part in every load have the same problem, in the same area?

Coating thickness on the light areas match the coating thickness in the dark areas?

Water quality of the rinsing you are using?

Dye tank evenly agitated, and filtered?

Could use a bit more info on your process.

Marc Green
Marc Green
anodizer - Boise, Idaho


July 15, 2014

A. I agree with Mr. Green who commented first. If your rinsing is inadequate, you will see this appearance. My advice, you must wipe it with clean fabric and clean water. If wasn't useful, you must empty your rinsing baths (after anodizing and sealing rinsing) and refill with fresh water. You won't see same appearance. But you must consider rinsing as cleaning, especially after anodizing and sealing.

alaattin tuna
- sakarya,turkey



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