Formulas for brush plating solutions for gold plating

A. Hi, Frank. It's fairly complicated, and brush plating solutions must be concentrated and probably have thixotropic agents added for thickening.

Even if you know the formulas, it might not make sense anyway. Gold is so expensive that the tack-on costs of the proprietary chemistry are usually a fairly minor mark-up, so I know of no professional platers or jewellers who risk losing very expensive gold to poor plating to try to save a little bit on the carrier chemicals.

The thing in your favor, though, is that car emblems are the easiest thing in all the world to plate -- because all you are doing is taking an item that was polished, pretreated, and beautifully nickel plated to OEM quality, then stripping a few millionths of an inch of chrome from it and replacing that chrome with a few millionths of an inch of gold. Prep is at least 90% of the work in plating, and none is required in the case of gold plating nickel-chrome emblems :-)

Good luck,

A. Ferrocyanide gold bath (late 19th century):
2,65 gm gold chloride
15 gm potassium ferrocyanide ⇦ this on eBay or Amazon [affil links]
15 gm sodium carbonate ⇦ this on eBay or Amazon]
1 lit water
Stainless steel anode, 2-6 V / 0,5 A/dm2
In boiling water dissolve ferrocyanide; when dissolved, add carbonate; when it is dissolved add gold chloride and boil it a minimum of 30 minutes.
Must be filtered (cold) and then you can use it. Never mix it with acids!
Only grease and oxide free objects can be plated!

A. Hi J. The Metal Finishing Guidebook or the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] would be good starting sources for 'recipes' for plating solutions. Brush plating solutions are usually more concentrated, closer to a gel, than bath plating solutions -- possibly with barium sulphate or fumed silica as thixotropic agents.

But a quick word of warning for others who may be reading this is that electroplating is about process sequences not recipes. A rule of thumb is that 90% of the effort and plating problems are pretreatment issues. If the substrate is properly prepared, it will usually plate well; if it isn't prepared well, all efforts towards plating it will usually be wasted.

A. The only place that I have seen home brew formulas readily available, was several years ago in the Metal Finishing Guidebook. The article was by an engineer at Boeing. Check with Metal Finishing to see if you can get a copy.

A. Hi, Alan

Europeans sometimes use commas as a decimal point where people from the USA and Australia would expect a period. So, yes, 2,65 is 2.65 and the electrical requirement is 2 to 6 volts at a current density of 0.5 Amps per square decimeter.

Note that this formula involves dangerous cyanides.

Luck and regards,

24 Kt Gold Plating Solution

on eBay or

Amazon

(affil links)

A. Hi, Alan.

Goran is a metals conservator at a museum and, as you can see, he is a tremendous resource for historical metal finishing issues. But unless you are trying to replicate something from the 1800's, I personally don't think it makes sense to forego 120 years of progress and use a plating formula from Thomas Edison's early days, probably decades before anyone even thought of brush plating. I suggest, again, purchasing a modern gold plating solution that will deliver a proper deposit, rather than having to spend five or ten times as much applying a plating that needs to be five times as thick in order to deliver a pinhole-free coating :-)

But if you are going to mix up your own chemistry, I hope you are a chemist fully aware of the dangers of cyanide. Professionals never attempt to mix their own gold plating solutions as far as I know; the only people who do so are PhD students when trying to fully understand the influence of complex variables. Best of luck.

Regards,

A. Hi, Anh.

The brightener/hardener for gold plating is sometimes a metal salt such as cobalt rather than an organic material.

I am not familiar with the specific pink solutions you speak of. I suppose it's possible that some gold solutions have nano particles of gold, but in the general case, the gold must be dissolved as a salt, not be present as a particle, and I understand that small amounts of copper and silver steer the color towards pink. Good luck.

Regards,

A. Hi Doug. Please tell us what you are trying to do and why, because we are mixing apples and oranges in a confusing way, and I have little idea what we're even talking about :-)

Cobalt additives and organic brighteners were certainly not used in 19th century gold plating formulas. Thanks.

Regards,

A. Hi Doyle. It's more false than true.

Sorry for the communication difficulty, but when I asked you to please tell us what you are trying to do and why, I didn't mean what two or three chemicals are you trying to mix . . . I meant why are you trying to formulate a gold plating process, particularly one from the 1800s, what do you hope to plate with it (jewelry, electronic contact tabs, etc.), and to what end?

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


on eBay or

AbeBooks

or Amazon

(affil links)

You are clearly welcome to try to formulate a plating bath yourself, but just in case you don't know, people generally buy gold plating processes rather than formulate them because a thin non-porous layer from a proprietary bath costs much less and performs better than a thicker layer from home-brew, plus you get the benefit of the supplier's knowledge. In my own career of 40+ years in the industry, I don't recall a single plating shop that made their own gold plating solution from commodity chemicals (although some held as trade secret their manipulations to get certain properties like specific color).

Let's start with a table from Gold Plating Technology: .

You are trying to start with a 19th century ferrocyanide "color gold", and trying to add cobalt and/or an organic brightener like EDTA to it as if it were an acid hard gold plating solution. I don't think there is much chance for success. For one thing, you must be well into the acid range to get the cobalt to deposit. Further, quoting D.G. Foulke, in Goldie again, "The preparation of gold baths using potassium ferrocycanide goes back some 150 years, when alkali cyanides were impure and expensive while potassium ferrocyanide was fairly pure and cheap". The overall thrust of his comments is that the ferrocyanide itself has been found to not actually be a part of the process, and it's silly to use ferrocycanide now that we know better.

If you are looking for a "hard gold", this would be the "Acid" gold in Goldie's chart, with a simple cobalt salt added so it co-deposits as an alloy of perhaps 0.5% cobalt (although I understand that it's often premixed into the gold solution), and perhaps EDTA as an organic additive. So the direct answer to your question of when they are added is: not in the initial compounding, but after the initial compounding is done. Good luck.

Regards,

A. Hi Doyle. Further up the page I remarked that I didn't think anyone had heard of brush electroplating in the 1800's -- so I presume the formulation is for normal tank plating. I know of no reason why brass cannot be the substrate to be plated with this solution if we make the leap of faith that it works at all :-)

But I'll ask for the third time what you're trying to do -- because it is not our intention to lead you down dead ends, or toward dangerous chemistry, or obsolete processes, while leaving out important things you should be told . . . but there's no way we can even guess what you're trying to do or why, and therefore what we should be trying to advise you about. But best of luck.

Regards,

A. Hi. I have no experience with this 150+ year old process, but Goran is a metals conservator who feels it will deposit gold, and I have no reason to think it won't. But I'm still wondering why you're trying to do this rather than simply using a modern plating solution, but best of luck with it.

Regards,

A. This type of bath is very stable, relatively simple to prepare, without any free cyanide, and you can use it to gold plate brass (or any other copper alloy), silver, iron and pewter (according to J.Fischer, D.E.Weimer, Precious Metal Plating [on Amazon affil links], Teddington 1964, p.115). That type of bath is oldest cyanide-free gold plating process: 1841! (according to other sources thiosulphate bath). According to some sources still in use in Russia (Halilov, I.H. Galvanotehnika Dlya Yuvelirov,plating Handbook for Jewelers, Saratov 2003, p.38).

Hope it helps and good luck!

---

Thanks Goran!

Regards,

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

A. Hi Doyle. I think there is an assumption here that people still make gold plating processes by buying individual gold salts and other commodity chemicals and mixing them. But these days we tend to buy a ready-to-go precious metal plating solution, or perhaps a make-up solution and a replenisher. Large buyers would go to plating process suppliers like Technic or DeGusa; smaller buyers would go to jewelry supply distributors like Grobet to buy processes like the Clean Earth plating solution previously illustrated halfway up the page, or to hobby-scale suppliers.

For brush plating it is usual to go to a supplier who offers both the equipment and chemicals. Good luck.

Regards,

A. Somewhat late response:

(1) potassium ferrocyanide ⇦ this on eBay or Amazon [affil links] MSDS CAN BE OBTAINED VIA WWW - MIXING IT WITH WATER ( OR ALKALINE compounds) IS NOT DANGEROUS, BUT NEVER TRY TO MIX IT WITH STRONG MINERAL ACIDS!

(2) ??????

(3) 24 ct

(4) YES

(5) YOU CAN USE GLOVES AND SAFETY GOGGLES

Hope it helps and good luck!

Hi Dear Mark and David.
Certainly these will be helpful for me.
Thanks a lot.

A. Hi julaha. A crucial parameter when purchasing gold plating solutions is the gold content. That's how you know if you are getting gold or water. Everyone knows the approximate price of gold on a given day. Then if you are paying only 50% more than the price of raw gold for gold properly dissolved into a plating solution, you are probably getting a great deal; if you're paying 500% more, you are getting a bad deal. If a vendor won't tell you the actual gold content of their plating solution, so you can figure it out, you're buying from the wrong people. Good luck.

Regards,

 Hi Alex. You're certainly welcome to be disappointed; and you're also welcome to post your questions and see if they are answered -- we have tens of thousands of well answered questions in this forum.

Although we're happy to give grade school children detailed instruction on how to do basic zinc and copper electroplating for the purpose of understanding the science of it ("How Electroplating Works"), all sciences & technologies quickly advance beyond what can be explained in a few paragraphs, and then we have to move on to textbooks for deeper understanding, and to sponsored research for further development.

People might post questions on gene modification on other boards, but no one would expect to learn the field that way; nor expect people to explain the details of the trade secret splicing tools their employer has developed; yet people sometimes tend to feel that plating must be easy, and the experience & learning that a plater acquires in a lifetime can be summarized in a paragraph, and that people in the plating industry have no right to intellectual property but owe the world the proceeds of their decades of research :-)

books.google.com will have some old formulations, as will older textbooks, and scholar.google.com will show you some current research, but very few people know the formulation of the modern-day brush plating brighteners, thickeners, etc., that people are interested in; I've been in the plating industry for 50 years and don't know them. And the few people who do know them are not permitted to blow their employer's trade secrets on the internet. Sorry.

Regards,

 Hi again Alex. Thanks for the gracious follow-up.

There are certainly applications which the megacorps won't invest money into. These pages are replete with examples of how the big-money folks are uninterested in solving even the big problems let alone the small ones :-)
Vale bought International Nickel and the whole plating industry wasn't big enough for them to want to make S-Rounds anymore, leaving everyone in turmoil -- not to mention that International Nickel's long tradition of being a champion for the plating industry, sponsoring events and offering white papers on plating technology is apparently history. Elsevier Science, seemingly without even bothering to look for a buyer/successor, simply shut down Metal Finishing magazine, the industry's longest running publication, and stopped publishing the industry's best known and most popular book, the Metal Finishing Guidebook. Henkel apparently will not let their distributors sell less than a pallet load of maskant to end customers who won't use even one drum before the expiration date, and these pages are replete with complaints about that environmental travesty.

Yes, we're on our own in many areas with today's megacorps :-(

Regards,