Fingerprint stains & corrosion, on chromated zinc plated steel surfaces

A. The plater isn't doing anything wrong. Wear light cotton gloves when handling the parts and this will prevent the sweat attacking the surface. If your supplier can't answer this you have to ask if he really understands his process and that should start some alarm bells ringing in your head.

A. Sweat and finger oils are quite corrosive. Your plater is not necessarily doing anything wrong. We found out that one kind of hand lotion would strip yellow or OD chromate (which are a lot more resistant than clear by at least an order of magnitude) in seconds.

I would contact the American Zinc Association in Washington DC to see what their thoughts were for improving the situation. Alternative would be to contact a major supplier of zinc plating /chromating materials. The chromate is really a gel for up to 24 hours. Any contact prior to that is begging for trouble. One answer is to have your people wear clean gloves until you find a cure or at least an improvement.

A. There is apparently some anecdotal evidence that people who handle chromated parts are subject to an increased incidence of skin cancer. I have no information to offer either in support of this hypothesis or in refutation of it. However, considering this possibility, plus the very evident reaction between their skin and the chromated surface, and the fact that it is causing rejects, it indeed seems only reasonable that the handlers should be wearing gloves.

A. Mark,
White fingerprint stain on part, try to take part out after zinc plate and see any stain; if you have stain on part nothing wrong with clear chromate --stain is something wrong in zinc plate or precleaning problem. To run hull cell panel if you can duplicate stain problem run Hull cell panel.

A. I have worked extensively with the electronics and telecommunications chassis industry and have developed a sure fire 3 step program to solve your problems.
1. Wear clean cotton gloves when handling and assembling
2. Handle and assemble in an air conditioned environment and or provide sweatbands and towels for the handlers
3. Lower your expectations just a little. Problem solved!

A. I'm not familiar with your spec's so this may already be covered by your question. What kind of surface treatment does your zinc plating get? I've worked with tin/zinc plating and it finger marks very easily. Do you have some kind of passivation in place? I would expect cleaning prior to plating to remove finger marks, and I can't imagine people handling objects between cleaning and plating, so I would suggest your blemishes occur post plating.

A. I agree with Todd. The handling and housekeeping at the plater and the assembler are critical. I would also like to point out that many trivalent chromates (blue bright) tend to be very soft when applied for maximum corrosion resistance and handling of any kind should be avoided for these and all other chromate films for a minimum of 24 hours to allow the gelatinous chromate film to reach full hardness. Also, remember the human factor. Gloves are fine but the workers need to change the gloves when they get damp or you will just leave smudge marks instead of distinct finger prints.

For Todd: I bet Dave remembers this from his years up North.

A. As one who has some 30+ years of zinc plating on electronic cabinetry and some 15 years working on various spec writing committees including both ASTM and SAE, the problem looks all too familiar.

1) Go back to your plating house and insist they use a HEXAVALENT, clear chromate over the zinc plating. They've likely gone to a more environmentally friendly TRIVALENT or non-chrome conversion coating. These have far less protection*.

2) Your burn-in temperature is beyond the upper limit for chromates. Around 140 °F (60 °C) the hydrated gel-like chromate becomes dehydrated and the corrosion resistance of the chromated zinc drops off. All standard plating specs for chromates limit drying temperatures and final hot rinses to less than this.

3) Switch to a yellow chromate which offers more protection but probably won't meet aesthetic or electrical resistance requirements.

Lastly, and I can't believe Todd didn't suggest this, switch from zinc to electroless nickel. Nickel is FAR less prone to such staining and can more easily be cleaned, even with Windex Commercial Line ⇦ this on eBay or Amazon [affil links] !

----
* Ed. note: Note that this posting is from 2002 and probably doesn't represent Milt's opinion of the newer trivalent processes after 2 decades of advances.

A. Now that Milt mentioned it, electroless nickel does do very well and is used in that application. Especially when some of the panels are aluminum. The electroless nickel allows for RFI and conductivity that is not possible with anodize. The steel zinc plated panels of these cabinets have been switched to electroless nickel plating for cosmetic continuity.The electroless nickel plated panels are subject to the same pitfalls as zinc plating though.They will still stain , discolor, and fingerprint if mishandled.The EN plating can be restored by the customer if needed but the customer will likely be offended at this suggestion. High phos EN will somewhat alleviate the staining problem but the customer will still find fault with the plating.

Gene, Dave says hello.

Acetone

on eBay or

Amazon

(affil links)

A. Hi, Richard. You can certainly try acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! or MILD detergent (dish detergent) to remove the prints, followed by isopropyl alcohol as an anti-staining rinse, since none of these, daintily used, should hurt a chromated zinc finish much. Best of luck with it!

But the idea that numerous highly experienced platers, each with decades of experience, all misread a very simple question, is the actual misreading :-(

Rather ...

"The Moving Finger writes; and, having writ,
Moves on: nor all your Piety nor Wit
Shall lure it back to cancel half a Line,
Nor all your Tears wash out a Word of it."
    - The Rubaiyat of Omar Khayyam

The responders steered the discussion towards avoiding fingerprints rather than removing them in recognition that fingerprints usually cannot be removed. If the fingerprints preceded the chromate, they are under it and obviously cannot be removed without redoing the finish; if they were in the uncured chromate (the usual case), they're embossed into the finish, not on top of the finish, and can't be removed without redoing the finish; and if they sat on the finish for an extended time they probably have etched the finish and can't be removed. Sorry for the pessimistic appraisal of your chances, and good luck!

The right answer is that these days employees should be wearing gloves. If a dentist can do a root canal with gloves on, plating shop employees can do their jobs with gloves on.

Regards,

A. Hi Ana. The first thing to do is find out what spec you are plating to, and read whether it possibly restricts you to acetone because, if so, any other cleaner is disallowed. If you are not restricted by a spec, I have been led to believe that mild dish detergent or acetone should be okay. Good luck.

Regards,

A. Hi again. Then apparently you may use whatever you wish that doesn't harm the chromate. Again, I suspect that mild detergent without a long immersion time, or acetone, can be used without markedly impacting your salt spray time. I've heard of Simple Green being used as well. That doesn't necessarily mean that these cleaners will clean the chromate as you wish though :-(

As you see from the postings above yours, the dirt can be under the chromate (probably unlikely) or embossed into it (likely).

Regards,

A. Ahead of the bright clear chromate you need a FRESH 1/4%/vol Nitric Acid Dip.

A. Best way is to use double handgloves when handling Zinc plated parts.
1st layer-Surgical/rubber gloves
2nd layer: Cotton gloves
Using only cotton gloves can still leave finger print mark into the plated surface as some people still have sweating of fingers.

A. We are currently facing that issue regarding with our new parts & project -- except that our materials are aluminum with clear chromate/conversion. Our customer is concerned of course about the hand/finger print marks on our parts.
We tried all available solutions we have inside our company such as wipe out, thinner, retarder, etc. ... but the only solution that somehow works is the SCREEN WASH, which our subcon is using to clean their silk screens.
It surely worked!

BUT it is recommended to just give a very light rub and application of the solution to prevent damaging the chromate; take note also that the solution cannot go to artwork or silkscreen because it will erase and damage it.

Over-rubbing and application of the solution might end up the parts to damage its chromate and having dark spots.

During application you should wear cotton gloves and also use cotton fabrics for application and rubbing the solution onto the parts.

? Uh Oh, Let's start over. The headline says zinc plated steel where the chromate is fingerprinting. But the text says chromated aluminum. Which?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Sorry Robert, I caused the confusion.
She was not asking how to prevent fingerprint marks, she was offering help to the posters who had fingerprints on their chromated zinc plating by telling them how she removed them from her chromated aluminum. I suspect that her solution will prove applicable for chromated zinc plating -- but maybe not.

My own comment is that it's 2022, an age where my dentist does even tricky root canals while wearing gloves, and it's simply long past the time where any employees should ever be touching chromated surfaces without gloves :-)

Luck & Regards,

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