Metal finishing Q&As since 1989

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Hard black anodize, Type III without seal is fading

Q. WE HAVE PLATED A PART FOR OUR CUSTOMER HARD BLACK ANODIZE PER MIL-A-8625 / MIL-PRF-8625 [on DLA], TYPE III, CLASS 2 WITHOUT SEAL. NOW THE PARTS ARE FADING IN COLOR AND TURNING BRONZE-LIKE COLOR. IS THIS CASE NORMAL SINCE IT WAS SPECIFY NOT TO BE SEALED? PLEASE ADVISE. THANK YOU FOR YOUR INPUT.

HELENA NGUYEN
SHEET METAL FABRICATION - ORANGE, California, USA
2005

A. YES.
Seal will prevent the parts from fading/staining as rapidly but there is a trade-off.
A sealed part is less abrasion resistant (approx 30%).

I will inform my customers of the option to seal when I receive colored type III coatings.

Bill Grayson
metal finishing - San Jose, California, USA

A. That has been discussed hundreds of times at this site. try a search of the archives for more opinions.
Two things cause the part to fade, quality and type of the dye and quality of the seal. Since there is no seal, you will always get some fading.UV light is the culpurit and sunshine or flourescent lights have a lot.
All dye manufacturers have a fade resistance code. Look for the highest one possible. Note that it will be an organo-metallic dye and not a pure organic dye. It may affect the waste treatment of the rinse waters.

James Watts
- Navarre, Florida

A. Hard coat should not be sealed. The sealing molecule makes the coating softer.

All dyed anodized must be sealed or it will fade and/or bleed.

If your customer wants to comprimise standard procedure, then he must accept sealing, which, again, makes his coating softer and less resistant to Taber Abrasion Tests.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2005