Copper plating onto Silver

Practical Electroplating Handbook
by N.V. Parthasaradhy

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A. Hi Rick,

Copper plating onto silver is uncommon enough that I don't see it covered anywhere, even in N.V. Parthasaradhy's "Practical Electroplating Handbook" which includes a 77-page chapter just on prepping of the various metal substrates for plating.

I've never seen it myself, so getting a little history from you would be helpful -- for example, is this a new product and thus a new issue, or have you been having it done for a long while now? Is the shop that is doing it now the same shop which was successfully doing it before? Are the rejects a rarity or on all the parts. Does the plating just fall off, or is there some mechanical operation involved? Have you attempted to semi-quantify the adhesion with tape tests, chisel, mandrel or other testing?

Despite my unfamiliarity with copper plating onto silver, it is always necessary to throughly clean off any polishing compounds to a waterbreak-free condition (which hopefully can be done with aqueous based alkaline cleaning), and then to acid activate. Silver chloride is insoluble, so it is probably necessary to acid activate with sulfuric acid. I would then expect a sulfuric acid based copper plating to adhere properly. As a guess, it would not surprise me if the silver is getting exposed to chlorides which are de-activating the surface because hydrochloric acid is widely used in nearly all plating shops, and in many shops even the workspace air is laced with hydrochloric acid fumes..

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

"Gold Plating Technology"
by Reid & Goldie
-- hard to find & expensive; if you see a copy cheap, act fast!


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A. Hi again,

That general sequence (with cathodic cleaning) sounds okay to me, although as previously mentioned, copper plating onto silver surfaces is rare enough that I've never actually seen it nor read of it.

Silver is frequently gold plated though, and Reid & Goldie ⇨
discusses that in pretty good detail, including cyanide gold plating of silver ... from which it might be hypothesized that a cyanide copper strike would probably work well if consistent adhesion can't be achieved with acid copper directly on the silver.

Some history of whether you or your plating shop had prior success with plating acid copper directly onto silver vs. whether this is a new process without any proven success would be very useful. Although most plating problems are due to operational errors, electroplating theory can be very complex so it would be important to know whether acid copper directly on silver is or is not a proven viable sequence.

Your concern about contaminating the surface with city water is legitimate, and it's always better to rinse with de-ionized water ⇦ huh? , but the sulfuric acid must be rinsed before the parts go to the plating tank or the acid will soon cause an imbalance in the plating tank).

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

A. If unpolished parts don't peel but polished parts do, it is probably not the topography which is the problem because plating, unlike painting, does not need a toothy surface for good adhesion.

It can be difficult to remove buffing compounds with aqueous cleaning, and I suspect that this is the problem. Two possible next steps include:
1. Check for waterbreak-free surface really carefully. Any waterbreak indicates that some of that waxy compound is still there. Waterbreak-free draining should be observed after the second electrocleaning, and all the way through to the rinse before plating.
2. If the shop has a vapor-degreasing system, try it. If not, after the first electroclean, soak some sample parts in a good solvent before brushing them and putting them into the second electrocleaner, and see if this solves the problem.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

A. If the unpolished did not peel but the polished samples peeled, then I think the parts were not activated well. The polishing probably heated the parts slightly and formed a thicker oxide on the part.
Look at cathodic cleaning for a good H2 scrub and maybe cathodic acid, also H2 scrub.

"Electroplating and Electroless plating of Copper and Its Alloys"
by N. Kanani

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A. Hi, Michael. I have heard of rhodium plating silver jewelry as one approach to deterring tarnish, but I personally have not heard of plating copper underneath it. I don't see the advantage.

I do suspect that the edges of the items have higher current density applied to them and are "burning" ⇦ huh? (although I obviously can't see your setup); so reducing the voltage or getting the jewelry further from the anode may be the most practical way to attack this, short of changing the operating temperature or the composition of the plating solution. Good luck.

Regards,

Ted Mooney, P.E.

? Do I understand this correctly? You plan to expose your rhodium plating bath to copper contamination so you can avoid silver contamination?

Universal Plating System

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A. I compliment you for not putting nickel onto jewelry! The accepted substitute for nickel plating in jewelry is white bronze plating (almost universally used in Europe), but this is an alloy of three different metals and requires very careful process control, which may be beyond the skill and analytical facilities of many small platers. In any event it is a proprietary process, so you can find some vendors and talk to them about whether you can do it. But I think doing the rhodium plating directly onto the silver will be fine, although not chemically strippable in the event of defects. Good luck!

Ted Mooney, P.E.

Copper Plating Solution

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A. Hi Ursula. Yes, silver can be copper plated. But why are you using cupric nitrate rather than a simpler and much more conventional copper sulphate ⇦ on eBay or Amazon [affil link] based plating solution?

You say you are doing it ... while at the same time asking if it's possible. From this I assume it's not working satisfactorily for you, but please fill us in on the details.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

A. Hi again. I'm not sure I'm understanding what you are saying. You want to selectively copper plate, and apply the enamel grit to the copper plated areas, then fire the object? The plating has to be awfully good to survive that temperature, and although I have no experience heating silver to vitreous firing temperature, won't the exposed silver get terribly oxidized? What measures would be done to prevent that or restore the silver? Thanks.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

A. Enamels adhere very well to pure silver; 800,9 00 and 925 silver can be enameled too, but as far as I know you must use special base enamel if you want to use transparent colors. Copper plating must be very thick to survive firing in enameling kiln (0,1 mm at least). Hope it helps and good luck!

Incralac
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A. Hi Rob.
Copper plating onto silver ought to be relatively easy compared to some other plating assignments ...

While wearing gloves, scrub the silver with a scrub brush and a solution of pumice ⇦ on eBay or Amazon [affil link] and TSP (or Spic 'n Span ⇦ on eBay or Amazon [affil link] ). Rinse well, dip in 10-20 percent sulphuric acid, rinse, and then plate with copper plating solution, then lacquer it with something like Incralac (combination of sodium benzotriazole anti-tarnish and lacquer)

The principal issue though is to do a practice run or ten on some sort of silver scrap before risking your customer's goods. Copper plating is not as hard as playing basketball, but the same general idea applies: you can't just read how to do it and expect to be good at it your first time out :-)

Luck & Regards,

Ted Mooney, P.E. RET