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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Require Iridescent Passivation Solution
TUTORIAL FOR NEWBIES:
The word 'passivation' is general and slang-y, so in your reading, try to treat it more as a filler word rather than a specification.
In the case at hand, steel parts are often zinc electroplated, or zinc-alloy electroplated (zinc-cobalt, zinc-iron, or zinc-nickel). But after that electroplating they are invariably given a "chromate conversion coating" to increase the corrosion resistance and to deter white rust. This chromate conversion coating process is one of many processes which may sometimes be referred to as "passivation".
The zinc and zinc alloy plating with chromate conversion coating often exhibits iridescence but is usually rather strongly yellow, and is generally regarded as a functional coating rather than a decorative one. In this particular case Boris is apparently seeking a particular decorative look, strong in reds and purples.
Q. Good day. I require an Iridescent Passivation solution. I run a small line so I am interested to buy the minimum quantity. Please understand as international postage can be quite high, I am happy to pay what is possible to send a small quantity to suit a 120L tank.
Example of iridescent passivate finish:
- Perth, Western Australia
July 16, 2021
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
A. Hi Boris. What type of plating are you doing? Chromates applied onto zinc-nickel plating rather than onto zinc plating tend to show more of this reddish-purple tone. Even still, requiring a particular decorative look from what is generally considered a functional finish is perhaps going to take some work on your end, not just chemicals :-)
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2021
Q. We do zinc plating. We have been in contact with suppliers who provide chromate conversion solutions that impart an "iridescent" finish. One supplier who I contacted directly had many different types and replied being very keen to send a smaller quantity however later replied mentioning minimum order quantity is 1 ton.
The only supplier we have access to in our city can order most things from Macdermid Enthone of which we use a few of their products that come in 20L containers. Anything that is not kept in stock we must know the product code first before enquiring with them.
A lot of our work is not so much industrial where function is often key, however it is automotive and restoration where people are trying to get a similar finish to what may have been on the car from factory, nothing can be exact and we well understand this. We do our best within our plating line including putting clients' jobs on individually so we can get the hue of their finish more toward their desires. I used to use various plating shops myself but parts kept being lost in the tanks, contamination issues, etc. Fast forward to today I had become close friends to an electroplater who is now retired and we have started our own line for smaller jobs that require extra care and attention.
We notice some parts, mainly from Japanese cars and parts do have this iridescent looking finish. It appears to be much more common in the Asian market and some countries in Europe.
Boris Siljanoski [returning]- Perth, Western Australia
July 16, 2021
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
A. Hi again. Hopefully a supplier will reach out to you, and hopefully they will tell you that my knowledge is dated, but I think the items in that photo are zinc-nickel plated rather than zinc plated ...
Iridescence is not a color that comes from a dye or pigment -- even a drop of motor oil on a mud puddle will give a rainbow iridescent shine. It's cause is the fact that a portion of the light hitting the surface bounces off the top of the chromate layer, while a portion travels further passing through and bouncing off the plating. The paths being different lengths gets the two halves out of sync, augmenting some wavelengths and attenuating others.
I noticed years ago, when zinc-nickel first became popular, that it showed far more reds and purples, and far less yellow, than the chromated zinc plating I had long been familiar with. Presumably this was because the chromate was thinner because it reacted differently with the zinc-nickel. Things are different these days, with many different approaches to gaining/hiding iridescence available, but in my limited experience this looks like zinc-nickel plating :-)
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2021
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