Preventing Tarnish on Gold Plated Silver & Brass

A. Daniel, if I am understanding correctly you wish to plate over a brass substrate. If you are not currently permitted this is a problem. First a copper cyanide strike followed by copper plating (acid copper). Then the copper must be activated followed with bright nickel. Then the gold. No matter how thick the nickel or gold plate is, the brass (zinc/copper) will migrate without the nickel. The copper allows the nickel to adhere.

You may want to pursue a brush plating kit.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan

A. Hi Mike. Yes, insufficient thickness, and sulfur in the packaging, are both problems. Two obvious conditions that can lead to tarnish are porosity due to the gold wearing away or having been too thin from the get-go, and diffusion (molecular level intermixing over time) of the gold with the silver or brass such that the surface is no longer pure gold. While the obvious answer to both problems can be very thick gold plating (gold plated pocket watches have easily lasted a century), gold is very expensive, so other answers to the wear problem and diffusion problem have been offered.

Some of the answers to the wear problem have included:
- The application of titanium nitride in addition to or in lieu of gold plating because it is hard, relatively cheap, and looks very much like gold.
- E-coating or other clear coating that can let the gold show through, while increasing the time before it wears away. Properly done, it will not peel off.
The answer to the diffusion problem can be a barrier layer of nickel or other metal which is more resistant to molecular diffusion.

How thick the gold should be is complex because wear on rings might be a hundred times as severe as wear on pendants, and because it depends on whether gold thickness or another material are your primary barriers against both wear and diffusion, and what standards you want to hold yourself to in providing real vs. fake.

Those old pocket watches might have had 200 microns of gold plating, super-high quality heirloom plating on $10,000 luxury watches today is about 20 microns, very high quality costume jewelry is often about 2-1/2 microns, most "nice" quality costume jewelry is probably 1 micron, but thickness can go down as low as 1/10 of a micron on really cheap stuff or where TiN or clear coating are providing the wear resistance. Good luck.

Regards,

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

A. Silver, copper, and zinc will walk right through gold with time and/or temperature. You must have a diffusion barrier of nickel or palladium between the silver, and/or copper, and/or brass.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

A. If gold is plated directly on silver, copper, brass, etc., these metals will migrate up through the gold and produce tarnish on the surface. The thicker the gold, the more time it will take but, in my experience, it will eventually happen. For this reason, an adequate thickness of nickel is commonly plated underneath the gold to act as a barrier to this migration. The gold, itself, should not tarnish unless it's of a very low karat.

I would first suspect the nickel as being too thin or not being there at all.

Chris Owen
- Nevada, Missouri, USA

A. By federal code gold electroplated jewelry needs at least 7 micro-inches thickness of gold. Heavy gold plate and Vermeil must be at least 100 microinches thick. Very often jewelry made in the third world does not meet these standards. To prevent tarnish a barrier layer of nickel or palladium should be plated over brass and silver before gold plating.

Neil Bell
Red Sky Plating

Albuquerque, New Mexico

A. I used to work for a fine jewelry Co. in Newark,NJ.
We developed and marketed 18 kt gold electroplate brass jewelry with lifetime warranty. At that time there was no standard (astm, mil-spec, etc.) that met our requirements. We developed our own.
Good Luck,

Hamilton M. Solidum
- Mays Landing, New Jersey, USA
July 22, 2010

A. Hi Ruby. We'll try to advise Hamilton of your questions, but he hasn't posted on this site for going on 9 years, so we're not confident.

Assuming we don't reach him, you can probably increase interest & participation from the readers if you tell them about your own situation. Some people rely on clear coats, others rely on TiN and similar PVD coatings, and still others rely on thick, hard, gold. That jewelry manufacturer in Newark was famous for their tri-color (green, pink, yellow) gold jewelry items. Thanks.
Luck & Regards,


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

A. Hi David.

If a process has been working fine for you for 30 years, pragmatism suggests that you not change it :-)

Mouthpieces never get above room temperature or body temperature, so diffusion is slow. They are not soldered, so no concerns of intermetallics messing things up. They are not electronic components where ultra-low contact resistance must be guaranteed. They are not fine jewelry where the slightest off-color could be a killer issue. Adding a nickel layer would be adding many potential complications, including possibly exposing people to a nickel surface (some people are genuinely allergic to nickel and others may be paranoid about it).

In short, it's working fine for your application so don't change it ... but don't go lecturing the Orlando shop that they don't need a nickel barrier -- their application is probably different, and they they probably do need it :-)

Regards,

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

A. I was just looking at a piece of 60+ year old Tiffany Vermeil.

It still looks like new.

Will silver migrate through gold plating if there is no nickel barrier? Yes. But if the gold plating is done well and thick enough, it won't happen in a lifetime.

I'm guessing, and it's only a guess, that at ambient temperature, the migration of silver through gold is no more than a few microns per year, so if you're plating, say 50+ microns of gold, your original customer will never have a complaint.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

A. Hi Pushpak,

Possible causes are:

1. Gold bath contamination (metallic and/or organic).
2. Poor water rinsing after gold plating.
3. Gold deposit porosity.
4. Storage environment.
5. Metal migration from substrate.

Regards,
David

David Shiu
- Singapore

A. Hi Pushpak. The only thing I'd add to David's answer is that, while your process is meticulous, with 6 different layers of plating ... If I'm understanding you correctly and parsing your phrasing the way you intended, a micron of copper and a micron of silver is hardly thick plating. I'm not sure that either is even non-porous.

Regards,

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

A. Hello Rahul,
Silver plate is not considered a diffusion barrier. I anticipate the fact that nickel can't be used because you are plating jewelry? Without a diffusion barrier you will continue to see tarnishing. Another advantage of a good barrier plate is that it provides good leveling characteristics, which covers imperfections like fine scratches. If nickel cannot be used, have you considered White Bronze? Palladium is also a good barrier plate, but is expensive and would play havoc on your bottom line. I am a little surprised that you are seeing tarnishing in a few days with 120+ microinches of gold thickness. With that thickness it usually takes longer for tarnishing to appear. In summation, consider a good barrier plate between the brass and the gold that has good leveling characteristics. Good Luck.

Mark Baker
Process Engineer - Malone, New York, USA

A. Are you doing rack plating or barrel plating? if you are barrel plating then you need to add some filler such as copper or glass beads that will keep the parts from scratching each other.

Mark is correct in that you need a barrier layer to keep the gold from diffusing into the substrate. if you can't use nickel then try iron or cobalt.

Pat Mentone
St Paul, Minnesota

A. Hello Rahul,
Before Acid Cu plate you will want to employ these steps.
1) Soak clean
2) Electroclean
3) Double cascade rinse
4) 5-10% Sulfuric acid dip
5) Acid Cu plate
6) Double cascade rinse
7) 10% Sulfuric acid dip
8) Rinse
9) Ni or Co plate
10) Double cascade DI Rinse
11) Acid activate
12) DI rinse
13) Au plate
The reason for a soak clean and an electroclean is that the soak clean will loosen the soil on the part and the electrocleaner will blow it right off. You may already be doing this after the buffing process. Moving farther down the line, you will want to get into the Au bath within 90 seconds after the acid activate. Ni has a tendency to go passive if there is a delay going into the Au.
Good Luck.

Mark Baker
Process Engineer - Malone, New York, USA