[mike]

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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EDIT

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.

[magisbladius]

  Sorry again, there was a misunderstanding between him and me (I speak English, he speaks Russian  ). This is probably final, since I tried to get every detail out. 

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.

[mike]

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%

[constant thinker]

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.

[billnotgatez]

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.