The authoritative public forum
  for Metal Finishing since 1989
-----

Class 3 Iridite colors

Hello,

I am a Design Engineer working on developing an electromechanical system for military use. I am using Iridite process on the inside surfaces of the device to achieve corrosion resistance. different vendors are providing different color finishes...and all of them claim to be MIL-C-5541 class 3. My questions are: what causes the color difference in the Iridite process...is it some additive? Is it possible to have a finish that is yellow and clear and be compliant to class 3 levels?

THank you.
Hari Nayar
Design Engineer

Hari Nayar
batteries - Newark, New York
2005

---

The color or Iridite coatings will vary. The yellow color shows a small amount of hexavalent chromium in the film Colorless is mostly trivalent chrome with a trace of hexivalent. All color extrems will pass type III salt spray requirements of the specification. Another way to pass type III is to use Iridete 14-2-clear as in the qualified products for the MIL-C5541. The Iridite starts yellow and is bleached clear using Hot water, or a very mild alkali in hot water.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2005

---

The biggest cause of the color differences is the use of different chemicals to achieve the finish. The applicable QPL lists a number of different proprietary mixes that meet the requirements, but each chemicals results in a slightly different appearance. After that, the operator has a huge effect on the appearance of any coat as well - even if using the same chemical.

If you really want the answer to your questions, and you want to know the benefits and limitations of the class 3 coating, download a copy of the MIL-C-5541 specification from the ASSIST website (you can get their through the links button on the main page of finishing.com) and read it over for yourself; it's only 11 pages and it will let you know exactly what characteristics you are designing into your part.

Jim Gorsich
Compton, California, USA
2005