Squall
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Gold Plating
Hi i was wondering if anyone here has any knowledge of how to gold plate copper. I understand that one must first plate copper with nickel then gold,
but i have no previous experience and would like to know what sort of methods i could use. I will appreciate any info or links if you have them to
share.
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Squall
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Actually i first want to know if gold plating is actually a good idea or should i just get it done by professionals.
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chemkid
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Cu + AuSO4 --> Au + CuSO4 should work, i think. Now the trouble is gold sulphate. Gold and sulfuric acid will do it. You will probably need conc.
sulfuric to dissolve gold.
Edit: I have no idea about your second post. I'm a chemist not jewler 
Chemkid
PS Please use the edit function (as i did) rather than double posting.
[Edited on 7-11-2007 by chemkid]
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Squall
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Thanks for the information and the tip.
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not_important
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It depends on what the purpose of the gold plate is. Different methods are used for decorative, hard plating for electrical connectors, high purity
gold for semiconductor bonding, and so on.
Gold plating baths often are cyanide based, although there are baths based on sulfite complexes of gold, others using poly-amines as the complexing
agent, and some direct displacement formula that are based on 'gold chloride' - AuH(Cl)4.
You can buy gold plating kits, both immersion bath and ones that use an electrode something like a felt pen "magic marker". While these cost more than
making your own solutions, much of the expertise needed is packaged up in the kit meaning a lot less to learn. A search for "gold plating kit" will
find you many examples.
http://www.pfonline.com/articles/pfd0022.html
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YT2095
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I`ve done very thin gold plating quite successfully using gold chloride here also, IIRC it`s important to keep the soln very weak 1:100 would be the
strongest I would go, lower is fine also!
and it will plate Iron or copper quite nicely providing the surface is spotlessly clean, it will probably do other metals also, but those are the 2
that I tried.
there`s no need to use electricity either, just a piece of cotton wool soaked in the soln and then rubbed on the metal surface.
edit: here is an example: http://www.scienceforums.net/forum/showpost.php?p=211502&...
[Edited on 8-11-2007 by YT2095]
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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kilowatt
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Your best options if you want a bright shiny non-porous finish would either be to buy a commercial gold plating solution, or prepare a gold sulfite
plating solution which is pretty much the same thing. The reason I even suggest the former is because the latter is not really a simple undertaking.
However, it can be done according to the procedures in patent 6126807. There is also a more common route to gold sulfite in the industry which
involves gold fulminate, a sensitive high explosive which you would probably rather not deal with. The method in patent 6126807 should work quite
well. It describes the exact procedure. I would imagine "professionals" don't use it because it's still under patent.
I've seen a lot of people on a particular plating forum say that there is no way you can prepare a quality old plating bath, and that only
professionals may do it (this coming from people who make a profit off gold plating...). The methods are out there, though, and you actually can do
it. It's just chemistry.
You could also use a gold cyanide bath, but a sulfite bath is less problematic. Gold chloride and other simple electrolytes can also be used, but it
is difficult to achieve a good finish with them especially if you want it thick. If you scrounge enough you can find more info.
[Edited on 9-11-2007 by kilowatt]
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Fleaker
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Potassium gold cyanide, with some free cyanide will do the trick. There are various books on it.
Sulfuric acid does not dissolve gold to my knowledge at room temperature, it would probably have to be very hot. You can dissolve the oxide in
sulfuric.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Squall
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I will be plating jewelry pieces so i don't need to thick of a layer but it would be nice if the plating was even and shiny. I think i will go with
kilowatt's advice and buy a commercial gold plating solution. If not I am sure i can make my own gold sulfate solution. As always thanks for all the
advice.
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not_important
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If you're only doing a few pieces then I think buying a ready-made solution is the best way. If you're planning to do many pieces you might consider
making your own solutions.
Gold plating on jewelry often has a bright nickel underplate, and gold plating bath contains 'brighteners' which can be organic compounds and/or small
amounts of other metals.
I've not seen a sulfate based gold plating solution, but there are sulfite based ones. Most plating solution start with gold chloride, sometimes
using aqueous ammonia to precipitate the gold and then dissolve it in the solution base (alkali cyanide or sulfite for example), or just react the
gold chloride solution with the complexing salt.
Here's one of the first patents on sulfite based gold plating solutions.
Attachment: US3057789A1.pdf (154kB)
This file has been downloaded 645 times
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JohnWW
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| Quote: | Originally posted by chemkid
Cu + AuSO4 --> Au + CuSO4 should work, i think. Now the trouble is gold sulphate. Gold and sulfuric acid will do it. You will probably need conc.
sulfuric to dissolve gold. |
NO! Au is below H on the electrochemical series, meaning that an ordinary acid cannot dissolve Au. In fact, of all known metals, only Pt, Ir, and
probably elements 111, 110 and 109 (if ever they could be isolated in macro-quantities) are below Au on the electrochemical series.
Only either an oxidizing acid like aqua regia (e.g. a mixture of HNO3 and HCl) or a strongly complexing acid (like HCN) can possibly dissove Au. The
most stable simple compounds of Au in aqueous solution are those as anions of Au(III) from such dissolution, e.g. as AuCl4- and Au(CN)4-, and these
are most amenable for use for plating.
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kilowatt
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The methods I mentioned are for gold sulfite, not sulfate. It seems my original post contained a minor typo, but sulfite could be read all throughout
the context. Most commercial plating solutions these days are sulfite.
[Edited on 9-11-2007 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
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