Aluminum Anodizing Black Color Matching Problem

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A. Hi William. When black anodizing comes out blue the first step is to actually measure the thickness of the anodizing rather than assuming its thickness from the spec and supposed anodizing time. What is the actual anodizing thickness on the black and the blue pieces? Thanks.

Luck & Regards,


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

? What kind of sealing bath do you use? Most likely you use cold sealing. Up to me, source of problem is cold sealing. Please let me know your sealing

A. Agree with Ted. this color difference should be mainly caused by the ano film thickness.

A. I suspect source of problem is "low micron as 8 mic". Normally, even if a profile black anodized as 8 micron you would not get blue/purple color as your inquiry. My quess is this rack which got blue/purple one cold sealing duration time is much more normal sealing duration. As similar reason we always keep blackened anodized racks in cold sealing bath less than normal time such as instead of 15 min we keep 10 min due to prevent this problem. So even if you anodized 8 mic profile you will get brownish color instead of black color due to small pore structure

If you guys can figure out how to dye anodizing a good black when it is 8 microns thick and less, hundreds of shops around the world who are bearing the substantial extra cost of anodizing to 15 microns thickness will thank you!

A. Alaatin, the color you get with too few microns depends entirely on how the black dye is made. Some blacks are Blue, some blacks are Red. Black in itself is not "Black" but simply a high enough concentration of a dark pigment. If Black was actually BLACK, you'd probably see a grey with too few microns.

And you speak of Cold Sealing while replying to a post that states that they use Warm/Hot Seal.

Also, by lowering your sealing duration, are you not sacrificing longevity of the anodizing and colouring? There are typically a thousand good reasons why someone has dictated the longer sealing time, contrary to your shorter time.

A. Absolutely, Two-Step Coloring or Electrolytic tends to go more brown-ish if using Copper or Tin as the metal salts. I am not quite sure what a cobalt would produce however. Personally my experience is with Tin for Bronze and Black colors such as the Euras C31-35 range. And too few microns here, can lead to a brownish color, as well as too short coloring time. In regards to layer thickness on Architectural. Ordinarily, people recommend 20-25 µm for outdoor work and 15 µm for indoor work. Though if no color is needed 10 µm isn't unheard of. Every now and then some genius will ask for 10 µm electrolytic black and either you end up with issues either with the color and thus the customer, or you end up going higher microns. You can push below 15 µm but it is sketchy in terms of consistency. M Stammerjohann - Horsens, Denmark A. Stammerjohann, I have been using inorganic dye (tin sulphate) more than 15 years on anodizing line. I have not any experience in organic black dye process. If you use organic dye then your comment can be true. I respect your criticism and comment but I responded to this inquiry according to only my own experience. I insistently say again low coating thickness means as 7-8 microns narrow pore structure so tin deposit won't be enough for black coloring; that means you will get brownish color. Therefore to obtain black color, anodizing thickness must be 15-20 mic as Ted said. It's proven scientific fact... On the other hand, I considered warm sealing as cold sealing. I read some anodizing article regarding sealing process that is being mentioned cold sealing as room temperature sealing. Also I have no intention of lowering anodize quality while keeping shorter sealing duration. We have been testing sealing quality regularly, daily by some tests which are approved by Qualanod such as weight loss, spot test -- believe me, there is no problem with results. By the way I appreciate Ted's explanation before post. ALAATTIN TUNA - TURKYE Sakarya July 4, 2024