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topic 18493

Silver Plating Discoloration -- turning pink


(2002)

Q. Can someone out there help me by providing your expert advise on the root cause and corrective actions for this silver plated surface discolouration problem. I saw some discolouration (turned light pinkish) on a 0.4 ~ 0.5 µm thick silver flash of the connector pins after subjecting to 175 °C baking for about 1 hour. The connector base metal is copper.

KarPin Teoh
- JB, Johor, Malaysia


(2002)

A. Sounds like the copper is showing through. Try putting on a bit more silver. If you don't want to do that, try a pulsed current or ultrasonic agitation; either should reduce the porosity of the deposit and it may just be enough to stop the copper showing. Another way may be to put down a layer of nickel or tin to disguise the copper colour. However, be warned that tin will migrate into the copper and form an intermetallic compound and you probably do not want that!

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


(2002)

Q. Hi Trevor,

Thanks for the advise. I was wondering why I did not see this pinkish color before baking. It showed up only after 1 hour bake @ 175 °C. Hope you can shed some light on this.

KarPin Teoh
Universal Components - JB, Johor, Malaysia


(2002)

A. I suspect the silver is diffusing into the copper. If this is correct it will probably follow Fick's third law of diffusion in terms of rates. There is not a lot of silver on the surface, only 500 nm, so it shouldn't take too long to start to disappear at this temperature. Try putting on double the thickness and heating that to 175 °C for and hour and see if that discolours too. Alternatively try heat treating for less time to see how long it takes for the pink colour to appear.

Trevor Crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK



What causes silver plated jewellery to turn pink?

October 27, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I work with X-Ray Radiation Fluoresces to produce better plating for jewellery. What I am struggling to get a definitive answer for is, what causes silver plating to turn a very distinct pink colour once exposed to oxygen & sun light? The jewellery is made up of a brass base > acidic copper > Miralloy/white bronze > silver > polyurethane. Any help would be much appreciated.

Grant MIller
XRF Supervisor - England


October 27, 2015

A. There must be a diffusion barrier (nickel or paladium) between the copper bearing bronze and the silver, or the copper will come right thru with time, copper is "pink". (with and without sunlight and moisture.)

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como



October 28, 2015

Q. All the jewellery that we get in from our supplier has the same formula and 99% that comes through holds its own for years with the Miralloy layer between the copper & the Silver. Its just every so often a batch of the same piece will come through and after being hung by a window for 3 weeks it takes a very obvious bright pink colour, sometimes even a purple colour. We can not use Nickel as we work within the European law system & Palladium could be an option but is much more expensive than Miralloy.

I didn't know if it could be down to the way the batch gets plated? E.g., the temperature being too high or too low, the current density being too high or too low, cyanide content or even a wrong mix of Miralloy as Miralloy should be made up of 55% Cu 30% Sn & 15% Zn, Maybe this could be an issue.

If you have knowledge that could push us in the right direction, that would be great.

If we knew the direct cause, then we could catch it & tackle it sooner.

Thanks.

Grant Miller [returning]
- Oxfordshire, England


November 3, 2015

Q. With doing some research & testing I believe I now know the answer to my own question. With looking into Fick's Law of Diffusion, it makes sense that the plating temperature plays a huge part in the pink/purple discolouring that is being shown in the jewellery. It would also explain why the pink appears at different times & in different strengths. If the Miralloy is plated at a lower temperature then recommended then the layer will become porous, allowing acid copper layer to seep through. If the Silver plated layer is also plated at a lower temperature then it will also become porous allowing the copper to seep through faster & stronger in colour. Different levels of porosity in the Miralloy & Silver will play a part in the distance of time take to turn X the strength of the discolouring.

If anyone has a better idea or see's a flaw in my theory, then please do pitch in.

Grant Miller [returning]
- Oxfordshire, England


January 13, 2016

A. Hi
Silver plating turning Pink even after E-Coat, is due to Excess Brightener in Mirro alloy reacting with silver and, in due course of time, changing the colour to pink-blue-black.
So, Increase your Rinses after Miralloy and after silver. Use Cream of Tartar /Organic acid to neutralize cyanide after Silver plating, and thorough rinses after that including soft water , DI water alternate and Hot water finally. Then go for PU.This will resolve the issue.

Panjala Mukesh
Imitation jewelery firm - Hyderabad ,Telangana , India



October 14, 2016

Q. Silver plated brass terminal has pinkish looking residue on surface in some places of part. This residue is removable by scotch brite.
Why does this happen and what is the chemistry of this residue?
How to get rid of it?
Thanks.

Michael Galperin
- Old Tappan, New Jersey, USA


October 2016

? Hi Michael. Are you the plater?
If so, what can you tell us about the plating process? Can you see whether the discoloration is in low current density or high current density areas or is random? A number of helpful ideas for potential causes have already been advanced, but it's hard to tell which to focus on and which are inapplicable until we have some data from you that lets us do so.

If you are the customer, do you have any plating specs? Thanks.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 18, 2016

A. While you are waiting for other responses and ideas, be reminded that if silver is plated directly onto brass (without a diffusion barrier of nickel or palladium) the copper and zinc will migrate right thru the silver and corrode on top. Copper corrosion products mixed with zinc are "pink". You must have a diffusion barrier.

robert probert
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina



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