Topic: Olive Drab Chromate on Acid Cadmium

Our Olive Drab Chromate on Acid Cadmium is coming out splotchy and hazy.

We have tried many different combinations of processing. Yellow chromate and Clear Chromate first, pH adjusting, Clean rinse water, and no good results.

Can temperature of chromate bath cause these issues.



Re: Olive Drab Chromate on Acid Cadmium

Relayer150, Thanks for the post!!

If you could provide a photo of this "splotchy, hazy" finish, I would probably be of more assistance. I will give it a try anyway.

First of all, what is the temperature? If below 50F, can you add some hot water to take the chill off of it? I am sure if you had a heater, you would be using, but "who heats chromates in a job shop?" If you cannot raise the temp to, let's say 60F, then try a longer immersion time (almost double what you would normally process).

Secondly, are you certain you are cutting the alkaline/brightener film over the cad plate? Have you changed out your "sour dip" or "post-dip" prior to the olive drab? Try making up a new "sour dip" if there is reason to think your current sour dip is contaminated or "old".

And last, what is the concentration of the Cr+6 in the olive drab and especially, what is the pH? Make sure the the Cr+6 is in parameter, then consider adding 10% of the makeup qty. of Part B and see if you overcome the "splotchy/hazy" look. Sometimes an imbalance of the two components will cause this appearance. Other times, it is a sure sign that the chromate is old, saturated with zinc or cadmium, and worst case, contaminated and the “law of diminishing returns” has set in.

I assume this is a 2-part chromate chemistry? You may very well just be out of ratio and are going to need to work delicately to get this back in sync. Most OD chromates are 1:1 Part A/Part B makeups, but this may not apply to your chemistry. Always refer to your Technical Data Sheet when troubleshooting your process chemistry, one mfg. may differ from the other.

Here are some bullets to re-consider, if you have not already:

-Chromate concentration.
-Acidity of chromate solution.
-Bath temperature.
-Immersion time.
-Drying temperature.
-Quality of plated finish.
-Load size processed.
-Agitation during chromating.
-Transfer times before and after chromating.
-Age of chromate solution.
-Impurities in chromate solution (drag-in).
-Rinsing before and after chromate.

Some variables will have only a slight effect, while others or a combination of several, will greatly effect the final finish. Most importantly, if you can work with your chromate on the level of a “bench test” in a beaker in the lab, or worst case, a 5 gal. pail or small tank. This can prove successful without the “wastefulness” of unnecessary chemistry being added to the process tank. And if you are successful, proportionally, you may make additions to your process tank.

Good luck!

Last edited by skelton (01/21/2010 - 04:34 PM)

Skelton, hOST


Re: Olive Drab Chromate on Acid Cadmium


See attached photos.

We feel this issue could be directly related the compatibility of Acid Cad with the Olive Drab Chromate. We did adjust the Temp and have the bath at 80 to 90 degrees which would be room temp for Florida but not now since its been cold. That did solve the "blotchy" look but we are still seeing streaking. Is there any products that a strictly for OD over Acid Cad in the market?

Thanks for the assistance...

Charlie Costello

Quality Director, Sun-Glo Plating Co.


Re: Olive Drab Chromate on Acid Cadmium

there's not a lot of folks out there with acid cad experience, that's for sure.

But your blotchy appearance could be a number of things. One is the base plate before the cad.That can matter more than you would think.different base plates generate quite a variation. Another issue is brightener. The more you have, the prettier the part....until it hits the OD. Sometimes wetter helps the OD to cut through, sometimes not. A little hydrogen peroxide in the acid dip prior to the OD goes a long way to cut the invisible organic film.It's hard to imagine, but the acid dip totally changes the part and it looks uniform, but add the hydrogen peroxide and it's a whole new world.  Go figure!


Re: Olive Drab Chromate on Acid Cadmium

We are using Iridite 1A OD for the chromate but we are getting a rainbow effect, how can we get rid of the rainbow effect.