Gold plating removal

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A. Hi B,
Unfortunately, without knowing the thickness of the gold and additional details it is difficult to know if there is any positive value to more than offset the cost. If, while wearing safety goggles [on eBay or Amazon], you are able to scrape any gold off with an Exacto knife [on eBay or Amazon] or razor blade, you could take those scrapings to a "We Buy Gold" store and see if they can tell you anything. You could also bring them one of the wheels and they might be able to help, although they generally want gold items not gold plated items.
If people tell you they are no worth anything, unfortunately they might be right :-(

Luck & Regards,


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

A. Hi, Thomas. Since you don't say what the watch case is made of, or what kind of finish you want to apply to it, I'm guessing you are trying to salvage the gold value of the watch?

The weight of gold per square foot for each millionth of an inch of thickness is .00147 troy ounces. If the watch is a moderately priced one from the last couple of decades the gold is probably about 20 millionths of an inch thick (about half a micron): that's .0294 troy ounces per square foot. If the gold plated area is 2 square inches, it's .00041 troy ounces of gold. It's about 25 cents worth of gold for a relatively recent watch. But if it's a really old pocket watch, the plating is a hundred times thicker and it could easily contain a substantial amount of gold. Please clarify what you are trying to do. Thanks!

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A. Hi Tom,

I am going to assume that you are seeking a way to remove the gold from the watch for refinishing purposes not for salvage of the gold. First of all many old watches had good thick plated coatings for longevity. If you are seeking to chemically strip the gold off the watch, it is difficult to do without attacking the threaded and fine mechanical portions of the watch (thin flash plated areas). If there is severe "brassing" (exposed base metal, i.e., brass or nickel, on the wear edges), the stripping chemistry even with buffers will attack the brass severely, long before the thick gold plating has been removed chemically. Chemical stripping is fine for gold coatings 2 microns or less, but you will still have the disposal burden to contend with.

Mechanical removal is the safest using small files and paper sticks. In many cases it is faster than chemical stripping, especially on old pocket watches with 20 microns or more of gold. The filings and "sweeps" can be sent to a refiner for reclaim of the gold. If you do a large quantity of watch refinishing it is worth it.

Hope this helps, Good Luck.

A. Mr.Tomcik,

First check out what is the base material. If the base is brass and under coated with Nickel you can strip using sulfuric acid/glycerol based stripper, or sulfuric acid/copper sulphate based stripper. If the base is SS you can strip it with sodium cyanide solution. If a electroplated watch whose effective surface area is between 0.10 to 0.15 sq.dm is plated for 3.0 to 3.5 micron it will have approximately 40 to 80 milligrams of gold.

A. Hi, Howard. Please carefully reread David Vinson's reply -- I think it's what you are looking for. You need to find a shop who will mechanically polish the gold off. Good luck.

A. 1000 ml H₂SO₄ in 2000 ml Pyrex casserole dish with approx. 1/4 teaspoon of glycerine well mixed into the H₂SO₄. Submerge a lead bar or rod in the dish with enough of the metal sticking out to connect the negative (-) lead. Obtain a variable power supply (10 AMPS MAX) @6-12 volts -- a battery charger [on eBay or Amazon] works great!). Connect the negative lead to the lead electrode. Connect the positive (+) lead to a cable with STAINLESS STEEL ALLIGATOR CLIP. Attach the item you want stripped to the clip, turn on power supply and lower the piece you want stripped into the acid/glycerol solution. PRESTO--CHANGO! The black residue is approx. 95%+ pure gold. You will need to dissolve and purify product with Aqua Regia or HCl and regular Clorox Bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon] (halide leaching). This is simple, safer than HNO₃ fumes. I have been using this for years with great success. Good Luck!

A. You can it resolve in AR and recover it with sodium disulphate that is known as recovery chemicals and wash it with DI water

Hi. While David is no doubt correct, the question for me is whether dissolving everything will be practical in an individual case. I don't know how you can decide until you know what you've got: purity of gold plating, thickness of plating, weight of brass compared to weight of gold, etc.

Regards,

A. Hi, Alexander; hi, Pookie. There are things that a competent person can learn how to do from written instructions, like painting a wall or baking a pre-mixed cake. And there are things that a person won't learn to do from step by step instructions, but only from practice with supervision, like rebounding a basketball well or piloting a jetliner. You can search the internet forever but you will never find step-by-step instructions for those things.

As you are discovering on this page, people do tell you that mechanically polishing the gold off may be a better way to go than trying to dissolve it, but they can't give step-by-step instructions for recovering the gold and not damaging the chain or flatware because it's an acquired skill. You can take it to a plating shop for removal of the gold, but almost surely this will cost money, not pay money, because the value of the gold is minimal compared to the effort in removing it. Good luck.

Regards,

A. Thanks, Jeff.

You are right that it is likely that the gold is very thin. I would saw one of the items in half and try to estimate the thickness of the gold with a jeweler's loupe or a microscope. Until you have some idea of the thickness, it's impossible to estimate the amount of gold that is there. Once you do know the thickness, it's relatively easy. If it's thousands of dollars worth of gold, it's worth it despite the difficulties. If it's $35 worth of gold (and it might be a lot less), it's not going to be worth the cost of recovery.

Regards,

A. Hi, Robert.

These cars are, as you know, collectibles. I think you'll get far more from selling it as is than from stripping it. But if you insist, then start by cutting the car in half and estimating the gold thickness with a microscope. You'll want to know how much gold is there (I suspect it's not much). I've heard of people scraping the gold off the contact fingers of printed circuit boards with an Exacto knife [on eBay or Amazon], and that may be the best way for you to get the gold off. Good luck.

Regards,

A. Hi Sham. Do you have any reason to suspect that these gold spots contain significant gold value? Usually gold plating is thinner than a micron; sometimes much thinner. You might find 25 cents worth of gold or less, after investing a lot of time, and spending much more money that that for recovery tools and chemicals.

Gold recovery is serious business, so the first step is determining how much gold is there. Good luck.

Regards,

A. Hi Sham. As we've said repeatedly, recovery of gold is quite serious business, and step 1 is determining how thick the gold plating is. This is absolutely essential, not just to know whether the effort is worthwhile, but to track the gold content through each subsequent step so the appropriate amount of chemicals can be added a each step.

Anyone who skips this essential step is just playing, and playing with very hazardous chemicals to boot. So, please start by telling us how thick the gold plating is. Thanks!

Regards,

A. When using aqua regia (AR) to dissolve gold, most of the literature says to pre-mix it in the ratio of 3 or 4 parts hydrochloric acid (HCl) and 1 part nitric acid (NHO3). This will certainly dissolve the gold but, when attempting to precipitate the gold with a reducing agent, such as sodium metabisulfite, sodium sulfite, etc., you will find that the gold will not drop out. The usual reason for this is that some free nitric acid still exists in the solution. The gold won't precipitate until all the nitric is removed. The traditional method for removing the free nitric acid is to evaporate the solution to a syrup, add a few ml of HCl and evaporate further. This is repeated 3 or 4 times or, until all the nitric has been driven off. However, this is a time consuming cumbersome method.

A much better method is to not premix the 2 acids. The trick is to add the acids separately and only use enough nitric to dissolve the gold - no more, no less. Any combination of HCl and HNO3 will dissolve gold, even in a 100/1 or 1/100 ratio. An excess of HCl will not hinder the precipitation but any excess of nitric can cause problems.

Here's how I would do it.

(1) Put the material in a large beaker [beakers on eBay or Amazon] and barely cover it with HCl, only. To avoid the possibility of a foam-over, the material should not occupy more than 1/3-1/2 of the beaker capacity.
(2) Heat the HCl to about 65 °C on a hotplate. In case of a mishap or beaker breakage, it is best to first place the beaker in a ceramic dish that is made to withstand direct heat. The only one I know of that will do this without breaking is a Corning Ware "StoveTop" dish.
(3) Add a few ml of HNO3. You will observe gassing and the gold will start dissolving.
(4) When the reaction subsides, give the solution a gentle stir and add a few more ml of HNO3.
(5) Repeat until all the gold is dissolved. Stop adding nitric.
(6) Allow to cool and pour off the solution into another beaker. Rinse the material well, using as little water as possible. Save the rinses and keep them separate from the main solution.
(6a) If the only metal being dissolved is gold, there is probably a lot of life left in the solution. You could probably use this same solution to process more material. If you do this, follow the same procedure above.
(7) Combine the solution(s) and rinses. Add enough extra water so you end up with a total volume that is about 4 times the volume of HCl that you started with.
(8) Filter the solution until it is crystal clear.
(9) Precipitate the gold with the precipitant of your choice. I usually use sodium sulfite. About 2 grams will precipitate 1 gram of gold. I prefer to dissolve it in a small amount of hot water before adding it to the solution. If there is no excess nitric, the brown gold powder will start dropping immediately. If there is a little excess nitric present, the precipitant will first react with the excess nitric before the gold starts dropping. To make sure all the gold has dropped out, the solution can be tested by adding a drop to a spot plate (or white plastic spoon) and then adding a drop of stannous chloride solution (1 gram dissolved in about 20 ml of a 50/50 HCl solution diluted with water). A purple or black color indicates that there is still gold present in the solution. In that case, more precipitant is needed.
(10) Filter the gold powder, rinse it well with hot water, dry it, and melt it.

Notes:
(1) This process generates lots of noxious, toxic fumes and a fume hood is a must. Work with good rubber gloves and a plastic full-face shield.
(2) To get an idea of the acids needed, 1 troy ounce of gold requires about 125ml of HCl and 25-30 ml of nitric.
(3) Instead of using aqua regia, this gold plating can be dissolved in a combination of HCl/hydrogen peroxide (H2O2) or HCl/chlorine laundry bleach (sodium hypochlorite - NaClO). As with nitric acid, the H2O2 or NaClO should be used in small quantities. Before adding the precipitant, any excess of these can be removed by simply heating the solution for 2 or 3 hours. Get it quite hot but don't boil.

Wow. Chris knows his stuff!

Still, "nearly" 1 micron means less than 1/16 the thickness of light gage aluminum foil -- so I hope you have an awful lot of those bangles if you want to make money from it :-)

Good luck,

A. Hi Don. Looking at similar coins on eBay, they are not gold plated, and are listed for $12-$15 each. If yours are gold plated, I see no way of knowing, without testing, how thick the gold is . . . but I doubt that it's more than 20 or 30 millionths of an inch (you would have lost the engraving if the gold were thick). So do a calculation. Personally, I'd try to sell them on eBay or Craigslist rather than destroying collectibles. I'd suggest the same for gold watches :-)

Regards,

A. Hi Rumpelstiltskin. I think that engraving is in French and is saying "Plated with gold 80 microns thick". So, no, it's not solid gold; rather, it has a plating a little over 3 thousandths of an inch thick -- which is quite thick for gold plating.

Regards,

A. You have run into the problem of dissolving a highly chemical resistant coating (gold) without attacking the much less resistant substrate, usually nickel.
Gold stripping involves chemicals like cyanide and is certainly not suitable for amateurs.
Your best bet would be to take advantage of the fact that gold is much softer than whatever is underneath and easily wears away -- which is one reason that it is a very poor finish for bathroom or motorbike fittings. It is also very expensive so you can be certain that it will be thin!
Try a brass brush on a Dremel type hand tool [on eBay or Amazon]

A. Besides the gold, there is likely to be a nickel plated layer between the gold and copper. Both would have to be removed, probably using different solutions. Also, it is very possible that the solder has damaged the coin. Even if it hasn't, the solder must also be removed in a separate operation.

To remove these 3 things (gold, nickel, solder) would require some experimentation and the only thing you have to experiment with are the coins themselves.

In my opinion, it is unlikely that the coins could be successfully restored to their original condition.

A. Hi mohammad. Thanks for the kind words. But starting over will take us in circles, and exhaust the patience of those who have so helpfully responded already. Please try your best to phrase your questions in terms of the great answers already provided by David Vinson, Geoff Smith, Chris Owen and others. Thanks.

Regards,

Q. Hello,

I asked a question about how to remove rose gold plating on my watch. I forgot to mention that the base is stainless steel and that I have no intention to recover rose gold plating since it is probably fake anyways.

I hope this help answering the question. Thanks.

A. Dear sir, you simply polish that watch slowly until all plating is removed.

A. Hi Shammi. Chris Owen has told us the whole aqua regia process step-by-step above. Please ask for clarification on any step you did not understand. If you still prefer to go with the potassium cyanide approach, thread 12200 might be a better starting point. Good luck.

Regards,

A. Hello Sakshi, you can contact a precious metal supplier in India to supply you with a proprietary gold stripper designed to strip gold from a nickel underplate. There are non- cyanide gold strippers available as well.

A. Hi Xuelin. It is not necessary to remove the existing gold plating, but usually you won't get great shine from a thin gold layer unless it is atop a layer of bright nickel plating. Whether you (we know nothing of your knowledge or skills) will be successful in replating an old necklace of unknown material, in unknown condition, using an unknown gold plating kit, is probably beyond people's ability to guess though :-) If you can do good nickel plating first, I would have great hopes for you.

Luck & Regards,

A. Hi Sakshi. That's a broad question. The gold can be recovered by ion exchange, electrolytic recovery, or chemical precipitation. What is the gold concentration, and what other contaminants does the solution contain? Usually, ion exchange to capture the gold, followed by burning the resin, is the least expensive and most common approach.

Regards,