Olive drab Chromate Coating

A. Hi William. In this case the 'olive drab' IS the 'chromate coating'. Chromates are available in clear, yellow, black, and olive drab. Of them all, the olive drab chromate affords the most corrosion protection because it is the thickest and contains the most hexavalent chromium compounds.

A. I think it is less popular for aesthetic and economic reasons, Suresh. Although gold or yellow chromate was traditionally slightly lower in corrosion resistance than olive drab, it was less expensive and some people would say more attractive (sometimes even used to mislead consumers into believing they are getting brass).

These days color doesn't mean much though because RoHS chromates must be hex-free. The color of the old chromates was largely dependent on how much hex chrome was in them. Today, any color is probably dye, and the less dye and other adulterants, the better they probably work.

A. Mr. Suresh, I would say for both: technical and commercial reason. Green passivation (in fact there is a family of green passivation: olive, olive-drab, military green, grey and so on) is more expansive than any common yellow one. The aspect is also important. After yellow passivation zinc deposit is still metallic, bright and attractive. Green passivation eliminates metallic brightness and the aspect becomes less attractive for users. Except military users, who prefer non-reflective greenish coatings with high corrosion resistance to mirror bright ones. That's clear why.

A. Richard, I'd suggest contacting the manufacturer of the hobby plating solution. Unless we have an actual chemical formula to look at, our solutions are going to be guesses at best.

Hi Derick. As a general rule, inorganic materials don't suffer UV degradation and organics do. But yours is an excellent question to which I don't know the answer. Sorry :-(

Back in 2001, the color of olive drab chromate came from the hexavalent chrome in it; and olive drab was widely used on rough service military equipment, so I am quite confident of its UV resistance. But in these days of trivalent chromating, any coloration is probably just a dye, and organic dyes tend to not have much UV resistance -- so I'd love to know the answer myself :-)

Regards,

A. Hi Tim. If your concern is only with a manufacturing process, any hazards are always manageable; we work with things far more dangerous than hexavalent chromium all the time, and any dust/flakes can be safely sequestered through some procedure or other.

If, however, people will be touching or otherwise exposed to this component later in its life, personally I would rethink it. Automobiles can be and are built without hexavalent chromium in/on them despite their thousands of parts and very severe environmental exposure -- so it can be done.

Plus there are numerous European restrictions against hexavalent chromium, and if sold in California it would have to be labeled. But finally, carcinogenicity is a statistical proposition, not a cause & effect thing for an individual case. So if a person touches this object and happens to contract cancer, there is no way to say that exposure to this component was or wasn't the cause ... but what can be said is that they were exposed to a substance which the authorities and statistics have determined/demonstrated to be carcinogenic.

Regards,

A. Hi again. Talk to your plating shop or the major plating process providers about the possibility of a trivalent chromate for these zinc diecast parts rather than the somewhat old-fashioned hexavalent chromate processes.

The dusting/flaking when processing is not entirely surprising: some people feel zinc diecastings should be zinc plated before chromating (but I am unfamiliar with roll forming of die castings, and I don't actually understand what is being asked of the components).

Small parts can usually be barrel-plated or chromated in a basket or barrel rather than requiring racking, but I don't have a good understanding of your particular parts.

Regards,