[magisbladius]

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?

[ATMyller]

Gold is just too inert to actually make patina, but you can create a dark amalgam alloy using mercury.

[billnotgatez]

Mercury would be too toxic for jewelry.
Maybe there are alloys of gold that would be darker.

[Borek]

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.

[AWK]

Gold alloys used in jewelry darken under treatment with sulfur (but not  pure gold).

[magisbladius]

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).

[magisbladius]

My mistake, it does not have to pure (because it's an alloy )

[magisbladius]

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.

[mike]

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 

[magisbladius]

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.

[Dude]

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?

[magisbladius]

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.

[mike]

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?

[magisbladius]

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.

[magisbladius]

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