Cleaning Specimen Gold

[mirkaba]

I know this is a subject that has probably been beaten to death but I just seem to get comfortable.with the way I clean my gold and things take a new twist. I recently found a mass of crystalline gold in quartz and I have been wanting to etch the quartz away with hydrofluoric acid. So I took it into a friend who does this sort of thing and wow ...worked great!! I now have a beautiful, intricate and fragile mass of crystalline gold. The problem is this...It is not the bright yellow gold that I know it is. It is coated with a brown rust like residue. The specimen is too fragile to just clean in soap and water. Would heat and mild nitric acid clean this up? Does any one have experience with this sort of thing? Thanks..........Bob

 

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[nero_design]

Hi Bob.
There's a few things you can do to remove light staining although the aggressive nature of the Hydrofluoric Acid should have taken care of it for you. Since the stains are still there, it might be worth you taking a closer look as to the precise nature of the stains. You can soak your specimen for a few days to perhaps two weeks in a solution of Oxalic Acid (can be purchased cheaply from your local prospecting store). This is what I use myself to remove light staining. Some people use automobile "Rust Remover" since it contains a diluted amount of Hydrofluoric Acid (so be very careful). Nitric Acid should be your first option though. Then move on to other methods if this doesn't work. You have to be patient when soaking specimens in acids for long periods of time. Since gold is quite inert, you should be successful.

Do NOT use Hydrofluoric acid without researching just how deadly and horrific this stuff can be. The vapor alone will burn the corneas on your eyes and a couple of drops on your hand will kill you in under a week.

 

[mirkaba]

Thanks for the input. I am very leery of hf acid but I have a friend that uses it often. The piece has been in a 10% nitric solution for a couple days now and looks much better. When it is done I will post a pic...Bob

 

[jewelerdave]

Your very lucky to have someone who is willing to deal with hydrofluoric, I wont dare touch the stuff.

hydrochloric works well too. Just make sure if you use nitric to not mix the two if you want to save the specimen. When the two are mixed it makes aqua regia and that will dissolve gold. Dont do this unless you do some hefty research on refining.

I find that cleaning of specimens, and I have cleaned a lot of them. Usually only need a short bath in an ultrasonic cleaner.
The one I have is industrial grade and will pull oxides of tarnished silver sometimes, does a great and fast job of knocking off limonite and other odd ball stains and contaminants. Mud and dirt vaporizes in the thing.

Keep in mind for some collectors of high grade specimens they are purists and want the specimen just as it came out of the ground. Ie ultrasonic only, or just light washing.

I dont even use a tooth brush as if you have good crystalline gold any dirt can scratch the faces. If you happen to find a specimen with mirror" proof like" surfaces, It can make the difference from a $300 specimen to over $3000. So BE CAREFUL when cleaning if its crystalline gold.

Another way to get oxides off is to use jewelers pickling solution. Its a mild acid that will disolve away copper, and oxides only,
Its gentile enough to clean copper specimens with out destroying them, it just takes a good 5 to 10 min is all if the solution is warm. Great for cleaning gold and silver too.

Hope this helps, if anyone has any questions on cleaning feel free to PM me as I am happy to help.

Thanks,

David

 

[Hoser John]

easy to turn a treasure into trash and go blind in the process-BE DAMN CAREFUL with hf-john

 

[mirkaba]

The picture in the other post "Montana Gold" Was left over night in muriatic acid, neutralized and lightly cleaned with toothbrush and soap. Some of the iron oxide was left for contrast and a more naturale look. The piece cleaned in hf is still pretty dingy and I am waiting on an ultrasonic cleaner. It is strange how one piece will come out of the ground a nice buttery yellow and the next all green or brown coated and dingy looking. Thanks for the input...........Bob

 

[TomK]

Do NOT use Hydrofluoric acid without researching just how deadly and horrific this stuff can be. The vapor alone will burn the corneas on your eyes and a couple of drops on your hand will kill you in under a week.

This is a silly statement with regard to a couple drops on your hand will kill you in under a week. Completely FALSE!!!
I have worked with HF extensively and yes- I have gotten some on me with no ill effects. Don't misunderstand me- HF is dangerous but it will NOT kill you if you get a couple drops on your hand.

Tom