Non-Chemical Plated watch parts

[TomVader]

Hello all. I hope I'm posting this in the right section. I have a watch maker friend that I visit from time to time and he asked if I could refine some gold plated parts for him. I've never refined for anyone but myself but I said I would try. What he had was about three pounds of what he called "plates". I guess they are the frames that all the little gears get attached to. He said he got a huge lot of stuff years ago and these had been laying around collecting dust and he wanted to get rid of them. He said he thought they were plated with 10k gold but he wasn't sure. I acid tested one and it seemed to me that they were plated in 10k. A hard scratch on the stone showed as if it was brass, but a very light scratch showed 10k. I cut one in half and it looked to me like a brass core with a nickel plate and then a gold plate. I put them in a glass jug and poured in HCl and a little peroxide. For few days there was no change. After that I saw that the plating was coming off in flakes, revealing the nickel surface beneath. I thought, "Good, I won't have to dissolve all of that base metal." Every day I would shake the jug and pour off the acid with the gold flakes into a smaller container, let it settle, then pour the acid back into the jug, then wash the flakes into yet another container. I got about 95% of the gold into the small container and carefully rinsed first with well water and then three rinses with hot distilled water. Now I read somewhere on this forum that when karat gold is in small and thin enough pieces, there is no need to inquart, but to go right to nitric. What I expected was the nitric to be able to attack the base metals and leave me with partially refined gold ready for AR. Of course this is not what happened. The nitric seemed to have no effect. I saw no bubbles and it did not turn blue. I heated it; nothing. I left it for two days; nothing. I'm left with two possibilities: 1) the gold plate was already 24k. 2) the HCl leached out enough of the base metal and left me with purer flakes that won't be affected by the nitric. Any thoughts? Note: the flakes are a bright gold color. The HCl turned a dark dirty green color. Sorry for the lengthy post. I thank you in advance for your patience and expertise.

 

[Harold_V]

Indications are the resulting bits are akin to pure gold. If there was anything soluble in nitric, it would have been eliminated, assuming it's not alloyed with the gold.

I would have heated the nitric when treating the recovered flakes, as it has the ability to penetrate thin material enough to leach base metals, assuming the karat fineness is not too high. Being a plated surface, that is likely not the case, however.

What you do with the "spoils" should be dictated by your intended purpose. If you plan to market the recovered material to a non-user, it most likely will end up in the hands of a major refiner, where it would be purified. Thus, you should be able to simply melt and sell. By contrast, if a bench man purchased the material with the intended purpose of using the gold, he'd want to ensure it was pure, so it should be refined for that reason.

Harold

 

[TomVader]

Thanks, Harold. The gold is going back to the watchmaker most probably for sale. I'm being paid in knowledge. I guess the plating was 24k to begin with. I'll digest in AR and proceed normally from there.

 

[nickvc]

Tom from what I have seen most watch innards are plated in very high karat if not fine gold so the chances are if all the base materials were removed you would probably be left with a fairly good product.

 

[TomVader]

I'll weigh the flakes before the AR and then again after the drop just to see if there was something else in there.

 

[Harold_V]

I'll weigh the flakes before the AR and then again after the drop just to see if there was something else in there.

If there is, it will be obvious, as the remaining solution will reflect the content by the color you see. If the barren solution is colorless, it's pretty safe to assume it was pure.

Harold

 

[kmann1969]

Can you post some pics? im curious about the parts you are talking about

 

[TomVader]

I only saved one. My scale only goes to two decimal places. After weighing ten pieces I got an average weight of .44 grams each. total weight of 1,296.28 grams so roughly 2,946 pieces. These parts are shaped roughly as a semi circle, so I estimated the total area : pi R squared. if a circle 16mm then 3.14 x 64 = 200.96 mm square per piece (front and back). I read that a heavy gold plating was 2.5 microns thick. Since I don't have a way to measure anything that small, I used that value. So 200.96 x .0025 = .5024 cubic mm of gold per piece x 2,946 pieces = 1,480.07 cubic mm gold in total. Or 1.48 cubic cm. At 19.3 g/cm squared, that's 28.564 grams! Man was I WAY OFF. Either the plating was MUCH thinner or I screwed up my calculations. The yield is going to be closer to 3 grams!

 

[goldsilverpro]

My numbers are worse. Considering the holes, I estimated the total area on 2 sides to be about 1 square inch (645 mm2). That's about 3000 in2 for the lot. 2.5 microns is .0001". Therefore, there would be .0001 X 10.17 X 31.1 X 3000 = 95 grams of gold, assuming it was 24K.

I doubt if the plating is 10K. It's probably 18K or better. Any testing of any plating on a stone would be totally unreliable.

Sounds like there is still more gold somewhere.

 

[TomVader]

The watchmaker said he thought it was 10k heavy plate, so my thought was if I scratched very lightly on the stone I wouldn't penetrate to the base metal. I guess that's not practical. I purposely left out the edges and the holes to keep my estimate conservative. Also, if the plating was 10k, there's a different density value in that calculation. So 1.48 cm cubed x 11.57 = 17.12 grams, then the factor for 10k; x .417 = 7.139 grams fine gold. That's quite a bit closer to reality. The question is, if the plating was 10k, why no reaction with nitric? Is it possible that the HCl leached out most of the base metals and still left the flakes a shiny gold color? I doubt it, but IF that were the case, then maybe one could press carat gold in a rolling mill down to 2.5 microns and refine with HCl, thereby simplifying the whole process. Or at the least, process with nitric but eliminate the inquartation step. maybe when I get some time I'll take a small piece of 10k and pound it into a foil and put it in a HCl bath, then carefully weigh it, just to satisfy my curiosity. Thanks for your interest.

 

[FrugalRefiner]

It still depends on the alloying metals, but...

BEGINNING WORK
In outline, the method consists of the following steps:
(1) Preliminary treatments as required.
(2) If necessary, melting the material into a button and rolling it
thin, or granulating it.
(3) Removing as much base metal as possible with nitric acid.
(4) Dissolving the gold in aqua regia.
(5) Removing excess nitric acid.
(6) Recovering the dissolved gold with copperas.
(7) Washing the fine gold.
(8) Melting it.
(9) Saving the silver, if worth while.

(I) PRELIMINARY TREATMENTS
You first want to get your material in such form that it will be
easy for the nitric acid to reach the base metals and dissolve them.
The treatment will differ for different kinds of material.
Old gold jewelry, clippings, and old dentures should be hammered
flat and rolled thin, the thinner the better. Every minute at
the rolls saves many minutes at the acids. Feed the pieces into the
rolls with a little scoop whose sides have been cut out so that they
will fit against the rolls closely; or put them on a piece of paper,
and feed in paper and all.
Cut the rolled pieces up into short lengths, twisting them so they
will not lie flat in the acid; then anneal.

Dave

 

[TomVader]

Just an update: the weight before and after AR were the same (or very nearly so). So the flakes were pure gold, or I should say the plating was of 24k. Much, much thinner than 2.5 microns. Thanks everyone for your interest and your input.

 

[TomVader]

Oh yeah, the barren solution was clear and colorless. Thanks Harold.