Chemical Forums
Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: magisbladius on September 06, 2006, 12:07:00 AM
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My dad is a jeweler, who wants to know how to darken gold. Which chemical would be practical to use for the job; any good methods?
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Gold is just too inert to actually make patina, but you can create a dark amalgam alloy using mercury.
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Mercury would be too toxic for jewelry.
Maybe there are alloys of gold that would be darker.
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Mercury would be too toxic for jewelry.
Good point, although I will start with checking what is the mercury vapor pressure above amalgam, it can be low enough to be harmless.
Maybe there are alloys of gold that would be darker.
Question is ambiguous, as it is not clear for me what "dark gold" is. I thought that the original poster's Dad thinks about gold that looks like smoked. IIRC amalgam is not golden dark, but gray/silverish.
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Gold alloys used in jewelry darken under treatment with sulfur (but not pure gold).
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I spoke with some sort of chemistry professor today and realized my ambiguity.
Sorry for the ambiguous questions. He wants the gold to be tarnished, like silver which is easily tarnishable. The gold is 18 carat, has to be pure, permanent, and the method has to be quick and easy or at least somewhere close to being practical (not in a lab).
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My mistake, it does not have to pure (because it's an alloy ::))
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My dad said that someone told him it might be possibly done with iodine. If yes, would that work? How?
Another possibility might be sulfur. (I'm not a expert in chemistry, so excuse me for my guesses.) I did some minor research on lacquer and found out that it can corrode/tarnish compact discs. Compact discs contain various metals for their layers (can't remember if gold was included), and @ http://www.corrosion-doctors.org/MatSelect/corrgold.htm they mention gold can be tarnished by sulfur.
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What if you could use gold nanoparticles? Gold nanoparticles can produce an array of colors other than gold, many darker colors. If you could obtain a gold nanoparticle paint this might work. This is a vague idea though and I don't know specifics, but you could do some research. Gold Nano-Rings, you could charge a premium for them! Don't forget to send me a percentage of the profits ;)
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What if you could use gold nanoparticles? Gold nanoparticles can produce an array of colors other than gold, many darker colors. If you could obtain a gold nanoparticle paint this might work. This is a vague idea though and I don't know specifics, but you could do some research.
That won't work. The gold has to be tarnished somehow, then it will be polished black. Painting it is not what I'm looking for.
Gold Nano-Rings, you could charge a premium for them! Don't forget to send me a percentage of the profits ;)
Gold is gold -- you can only charge extra for labor, no matter what color it is.
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Electroplating is normally how one would modify the surface of a metal. The coloration is dependent upon the exposure time. Most efforts try to make something else look like gold on the surface. Why would you want gold to look like something else?
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After talking with my dad again, he just wants it tarnished and by the end when he is done with it, it should look black (he's not polishing, just to clear that up). The reason is for design.
He already knows electroplating and doesn't like it. He says that he saw actual tarnished gold at a jewelry store. I'll try getting a picture.
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Gold is gold -- you can only charge extra for labor, no matter what color it is.
I disagree, I think you would find the price of colloidal gold is relatively expensive. Gold is not always just gold!
I don't understand the problem, first, is he polishing it or not? Usually polishing will remove tarnish on gold.
Second, if he is not polishing it why not paint it?
Third, if he just wants it to look darker (ie not look like gold), why use gold at all?
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Gold is gold -- you can only charge extra for labor, no matter what color it is.
I disagree, I think you would find the price of colloidal gold is relatively expensive. Gold is not always just gold!
I don't understand the problem, first, is he polishing it or not? Usually polishing will remove tarnish on gold.
Second, if he is not polishing it why not paint it?
Third, if he just wants it to look darker (ie not look like gold), why use gold at all?
Paraphrased from my dad's mouth:
Colloidal gold is gold but dissolved in water. It's relatively the same
Paint makes the gold look shiny, which is not the look he is going for.
He almost killed me when I asked him your third question. Gold is a precious metal; he is not selling something like steel, silver, or bronze. I believe most people consider gold and diamonds at the top when buying from a high-quality jewelry store.
My next post will contain a link to a high-quality digital photograph of earrings I have in my hands that have the color/tarnish he wants.
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All the images are ~2mB. The lightning was a little bad, and the jpg format might not be good for this so please excuse the lackluster detail.
http://www.snapdrive.net/files/95591/DSC03950.JPG
http://www.snapdrive.net/files/95591/DSC03951.JPG
http://www.snapdrive.net/files/95591/DSC03952.JPG
Here are some more links incase the previous are broken:
http://www.quickdump.com/files/group/1725009060,847952137,84284546.html
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Well ask your Dad how much it would cost him to make colloidal gold, surely this process makes the colloidal gold more expensive??
Aldrich is seeling colloidal gold for AUD$114 for 25ml 0.01% HAuCl4 0.75A250 units/ml, 17-23 nm mean particle size. Is this cheaper than gold.
I suppose my point was that "nano"-technology is such a buzz at the moment that you could advertise "nano"-rings and charge an inflated price.
He almost killed me when I asked him your third question. Gold is a precious metal; he is not selling something like steel, silver, or bronze. I believe most people consider gold and diamonds at the top when buying from a high-quality jewelry store.
hmm yes but the idea is that gold and diamonds are so shiny and sparkley. Do people value dull diamonds and tarnished gold? I don't know. If it is a high quality gold item why would you want it to look tarnished? And then if it does took tarnished, who even knows if it is gold, in fact if it is tarnished it isn't elemental gold anyway!!
Use some other metal or alloy.
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I can't see where it is tarnished but it lookes like different textures to me. Maybe the trick is in texturing the gold surface to catch the light differently to make it look darker and lighter.
Here is a wikipedia entry on colloidal gold if you are interested http://en.wikipedia.org/wiki/Colloidal_gold
It is interesting how the color can change depending on the particle size.
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:o Sorry again, there was a misunderstanding between him and me (I speak English, he speaks Russian :P). This is probably final, since I tried to get every detail out. :o
The images contain jewelry which has been rhodium-plated.
He wants that color.
Unfortunately, the plates for rhodium-plating come off somehow.
Tarnished jewelry does NOT come off, and it can produce a similar yet a little darker color.
And when I mention colloidal gold, he says it's only used for medicine and not jewelry.
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Make sure you let us know if you find the answer. Sorry for not being more helpful. I am going to investigate colloidal gold paint now. Anyway, you should get your dad to read the article on colloidal gold, there are lots of potential uses for nanoparticles these days.
Here are some gold alloy colors if that is any help:
Yellow Gold, 22 Karat
Au 91.67% - Ag 5% - Cu 2% - Zn 1.33%
Yellow Gold, 18 Karat
Au 75% - Ag 10% - Cu 10% - Zn 5%
Red Gold, 18 Karat
Au 75% - Cu 25%
Rose Gold, 18 Karat
Au 75% - Cu 22.25% - Ag 2.75%
Pink Gold, 18 Karat
Au 75% - Cu 20% - Ag 5%
Green Gold, 18 Karat
Au 75% - Ag 20% - Cu 5%
Light Green, 18 Karat
Au 75% - Cu 23% - Cd 2%
Deep Green Gold, 18 Karat
Au 75% - Cu 6% - Ag 15% - Cd 4%
Blue Gold, 18 Karat
Au 75% - Fe 25%
Purple Gold, 18 Karat
Au 80% - Al 20%
White Gold, 14 Karat
Au 58.33% - Ni 15% - Cu 10% - Zn 16.67%
White Gold, 14 Karat
Au 58.33% - Pd 14% - Zn 11% - Ag 16.67%
White Gold, 18 Karat
Au 75% - Pt or Pd 25%
White Gold, 18 Karat (No. 2)
Au 75% - Pd 10% - Ni 10% - Zn 5%
Gray White Gold, 18 Karat
Au 75% - Cu 8% - Fe 17%
Yellow Gold, 14 Karat
Au 58.33% - Cu 31.2% - Ag 4% - Zn 6.47%
Yellow Gold, 12 Karat
Au 50% - Cu 34% - Ag 16%
Green Gold, 12 Karat
Au 50% - Cu 6% - Ag 44%
Dark Green Gold, 12 Karat
Au 50% - Cu 10% - Ag 40%
Red Gold, 12 Karat
Au 50% - Cu 50%
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Well, I have very little experience with gold, but I'll offer a few suggestions.
Your dad may want to try on small samples to see what gold halides look like (halides are elements in the halogen family, F, Cl, I, Br).
Gold will react with cyanide, I believe, but I'm unsure of the toxicity gold cyanides.
Also as a note, the halogens and cyanide can be extremely dangerous if proper safety precautions aren't taken.
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On many occasions tarnish may come off the metal showing the underlying metal. In that case the tarnish would be a false cover. Whether or not it is better than an inlay of an alloy would be the only question. Assuming that the inlay is prone to dislodgment.