No passwords, No popups, No cost, No AI:
we earn from 'affiliate link' purchases, making the site possible

Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

finishing.com -- The Home Page of the Finishing Industry

  The authoritative public forum
  for Metal Finishing since 1989

-----

Black dye turning purple over time

We are having a problem with black dyed anodize coatings turning purple over time-appear normal right out of processing. The hardware is anodizing in Type II (sulfuric). One piece developed this color substantially more on the side facing the room lighting. Does anyone have any insight on this problem? I should add that not all hardware is exhibiting this problem, only a very small percentage.

Teddy McCracken
- Blacksburg, Virginia

The problem may be in the dye itself, i.e., that you are not using the right kind of dye. Organic dyes fade. You need to look into some kind of inorganic dye, or integral color anodizing, or two-step anodizing if the exposure to light is severe. This is not to say that organic black dyes are not commonly used for interior exposures.

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

I'm not sure if you are the anodizer, or the end user of these parts..but your culprit is probably an improper seal of the anodizing. Other (but far less likely) possibilities are, not enough coating thickness to allow full dye penetration, or you are using a dye that has very poor lightfastness (but I think most blacks have good lightfastness).

Marc Green
anodizer - Boise, Idaho

The problem is probably due to either:

1) The dye used - different dyes have different lightfast & heat-fast ratings as to how well they hold up to heat & light.

2) The seal - if the part was not properly sealed the color could leach out.

David A. Kraft
- Long Island City, New York

The fact that the light fastness is only an issue with a small percentage of the parts would seem to remove the dye as the cause of the problem. If the dye itself had low light fastness, it would be apparent on a larger percentage. I think that you are on the right track with an improper seal.

Jim Gorsich
Compton, California, USA

You guys cheated, you read the question. That's the only reason your answers were better than mine :-)

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

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories: