Purple Gold........

[jdurg]

This is a neat, but expensive, little experiment used to make collodial gold which is a deep purple color and not the standard yellow color of gold. I do not have any pictures yet as I don't really have enough to get a good photograph of, but over time I will be trying to add more and more gold to this pile until I can get a nice photograph of it.

 

Anyway, to start out you need a few ingredients:

Gold metal (Any purity will do).

Tin Metal (High purity is better).

Nitric Acid (Concentrated).

Hydrochloric Acid (Concentrated).

 

Start out by making a small quantity of Aqua Regia with the HCl and HNO3. After the mixture has come together and cooled down, you add your gold to the solution. This will dissolve the gold and pretty much any other metal in there.

 

Once again, when it cools off you slowly add your tin to the acidic solution. It will dissolve in the acids giving off hydrogen gas. All the while, gold will begin to ppt in a VERY fine powdery form. This fine powder can have a beautiful purple hue to it, a magenta hue, a ruby red hue, or various other colors. It's really remarkable to see. In many instances, the gold will remain in solution and you'll have to wait for it to settle. Sometimes, it will never settle as the particles are just way too small. If the particles are large enough, you can filter it through some filter paper and wash it thoroughly with distilled water.

 

I will warn you that a significant portion of the gold winds up going bye-bye as the very fine particles stick to EVERYTHING and many times they remain suspended in the solution. So if you can get ahold of scrap gold, gold plating, and a bunch of other 'cheap' sources of gold it may wind up being a bit easier on the wallet. (I figure I only have a faint covering on the bottom of a tiny glass vial. Perhaps a few milligrams of Au).

[RyanJ]

Jdurg, thats cool, I'll have to try this.

I have high purity gold leaf here - would that work?

 

Alss, do you have an explination as to why this works

 

Cheers,

 

Ryan Jones

[jdurg]

Leaf may work pretty well. The whole process works because the aqua regia dissolves the gold and turns it into an aqueous species. When you add the tin metal, the tin metal will replace the gold from solution, but at the same time the gold will dissolve again in the aqua regia. What ends up happening is that the gold keeps dissolving and reforming as the tin and tin ions force it out of solution. This causes the gold to form as INCREDIBLY fine particles which reflect light MUCH differently than solid pieces of gold do.

[YT2095]

alternatively, get a little gold chloride on your fingers and wait an hour

 

a quick Factoid: the Purple color you see on expensive lenses (telescopes binoculars etc...) is actualy a vaporised Gold film, often little more than a few atoms thick

[woelen]

Another way to make really beautiful colloid gold (that is how it is called) is the following:

 

Dissolve some HAuCl4 in water. Approximately 0.0001 gram per ml of water, so you need ridiculously small amounts.

 

Prepare some sodium citrate solution, by dissolving citric acid in water, together with some sodium hydroxide. pH is not very critical, better a little on the acidic side.

 

Add this to your dilute HAuCl4 solution. Your liquid slowly becomes deep blue/indigo. You also can get red, yellow, purple, almost any color you like. The color depends on the particle size. Typical particle size is in the order of nanometers, each particle consisting of a few hundreds to several 10000's of atoms.

 

If you don't have HAuCl4, you can prepare some by dissolving gold in aqua regia. If you take 0.01 gram gold scrap, dissolve that in a few drops of aqua regia and dilute up to 100 ml with distilled water. With that 100 ml you can do many colloid experiments.

 

As I mentioned in the pyro-thread already (very off-topic over there), I use gold in my photography dark room. What I do is preparing photographic pictures, in which the image is built up of microscopic gold particles. These pictures have a remarkable deep blue color, VERY nice. When a silver sulfide image is gold-toned, then you get a beautiful red/purple color.

 

My toning solutions are extremely dilute. They contain up to a few % of thiocyanate, SCN(-), and somewhere between around 0.01% of gold. Even with 0.001% of gold you can do remarkable things. Now you can understand why 1 gram of HAuCl4, which seems very expensive, is not that expensive, given the use of it.

[YT2095]

Woelen, Interesting that you mentioned that, have you ever ried making your Own photgraphic plates in the past?

I`ve done it with the silver and the gold chlorides with reasonable success in the past, (even made my own camera to take these pics with), relating a little to you Kbromate thread, apparently gold bromide and silver bromides are also used, although I don`t know the exact proportions, it would be interesting to have a go yourself using some of these bromide salts etc...

and be nice to put on your site with pictures (of pictures) )

[RyanJ]

Leaf may work pretty well. The whole process works because the aqua regia dissolves the gold and turns it into an aqueous species. When you add the tin metal, the tin metal will replace the gold from solution, but at the same time the gold will dissolve again in the aqua regia. What ends up happening is that the gold keeps dissolving and reforming as the tin and tin ions force it out of solution. This causes the gold to form as INCREDIBLY fine particles which reflect light MUCH differently than solid pieces of gold do.

 

Great, I'll have a go as soon as my Nitric Acid arrives

 

And thanks for the description also

 

Cheers,

 

Ryan Jones