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Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: nero_design
Date: March 11, 2008 10:32AM
Not so long ago, I was curious about the methods prospectors use to clean their gold nuggets when required. A lot of sluice and dredge operators apparently bathe their fine gold granules in acids to improve the color. The Majority of collectors would agree that Gold Nuggets are best left in their natural state although this is often not always the case. However, most nuggets sold tend to have been cleaned via one process or another. I've found some great little samples here and there with my X-Terra 70 but not all are uniform in their luster. Some of the more porous surfaced nuggets seem to be dull and a little lifeless beside their shiny cousins.

Cleaning can be as simple as a soaking in water followed by a little toothbrush action to remove dirt. Soapy water is the usual liquid of first choice. In other cases, various acids of varying strengths and hazard are used to remove iron stains from 'tarnished' and otherwise 'unattractive' nuggets or even to eat away ironstone and quartz to reveal a more attractive shape.

For those who dig up their own gold, there's a lot of UGLY pieces that come out of the ground. Sure, it's all beautiful to me... but occasional pieces can certainly do with a slight improvement to their yellow metal hides. Some of the prettiest and most desirable pieces can be formed around iron ore. In a lot of cases, the gold content might be in low volume and delicate structure so removing it from the host-rock like quartz and ironstone is pointless and would lower the monetary value of the nugget.

I've seen some pieces that are a dirty-brown where iron oxides have leached into the outer surface of rather large nuggets.
Sometimes the quartz content ruins the appearance of what might otherwise be a beautiful collector's piece... especially if the quartz looks like 'snotty grey goop' instead of a stark or colored crystalline structure.

At present, this is what I'm doing to clean up the samples I've found so far:
1/ Wash the specimen in water and lightly wipe away any free dirt
2/ Soak the specimen in warm water for about 20 minutes
3/ Several 3-minute sessions in the ultrasonic cleaner (sometimes this is all you need to do)
4/ Careful removal of residual grains of quartz or sand granules embedded in the surface with a fine needle.
5/ (if required) A lengthy dip in a small container of Oxalic Acid
(rust & stain remover) to remove stains or break down quartz and Ironstone.

This nugget was acid cleaned to remove any host rock and to reveal the intricate shape of the nugget.

This specimen has not been treated with acid and retains it's unique shape and character with the quartz and iron ore host rock attached.

Some people are using Hydrofluoric Acid which is probably as dangerous as handling real nitroglycerin.
I heard two new stories today from a Prospector who had two of his friends affected - who spilled less than two drops of the stuff on their clothes or hands and the consequences of such a minor exposure (two drops or more is usually fatal within a short number of hours or days).

With Hydrofluoric Acid being a VERY efficient way to clean away host rock, quartz & ironstone, it's no wonder so many prospectors use it.
Unfortunately, it's not only GHASTLY stuff and considerably dangerous to store and use, it's being earmarked for restricted use by the FBI (if you live in North America). Using Oxalic Acid (usually sells for around $20 for a LARGE bottle of the powder to be added to water) is MUCH slower yet considerably safer. Unfortunately it takes many hours to remove iron stains and days to weeks to remove minor quartz and ironstone.

This is a $50 Ultrasonic Cleaner working on the small Gold Sovereign I dug up last year...

It's fun to watch the ultrasonic cleaner in action sometimes. When I placed a gold Sovereign into it, I thought the coin was clean and shiny to begin with... but as soon as I turned on the cleaner, small jets or plumes of red soil began to jet out of tiny pores in the gold surface. The results were completely different to my expectation since I thought the coin was already clean before I dropped it in. Same with nuggets which I thought were clean. Plenty of grey pipe clay and hidden cavities of earth end up jetting out as the cleaner is turned on.

The cleaner vibrates at an ultra high frequency which forms microscopic bubbles on the surface of the item being cleaned.
This in turn blasts away microscopic particles of dirt and larger materials quite efficiently. You have to be careful with fragile quartz specimens though in case the vibrations shatter the already fractured matrix.

What other methods do other Nugget hunters use for cleaning their finds?
Have you ever damaged or ruined a specimen you were cleaning?

Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: Steve in Idaho
Date: March 11, 2008 06:21PM
I clean my smooth nuggets in a small rock tumbler with dish washer soap, hot water, and strong ammonia, then tumble for about 5 minutes, then rinse in hot water. If I am cleaning specimen nuggets like you have, I use hot water with a strong solution of oxalic acid and boil on a small hot plate out doors then take the specimens out of the hot acid after about 5 minutes and rinse in a hot solution of baking soda, after they stop fizzing, I then rinse in hot water. Sometimes I have to repeat this several times to get the iron stain out. We get crystalline gold out of an old hard rock mine that we have under claim and sell most of the gold as specimens. The other we crush and smelt then send to a refiner.

Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: treasurefiend
Date: March 11, 2008 07:52PM
very informative

LOL thats funny......................N/T
Posted by: nugget71
Date: March 11, 2008 09:05PM

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Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: nero_design
Date: March 11, 2008 09:48PM
This sort of relates to nugget cleaning and might be useful information for the curious:
If I remember correctly, the famous "Welcome Stranger Nugget" (a gold-quartz mass of 70 Kilos of gold discovered in the 1800s) was first placed into the fireplace. The heat from the fire caused the gold to expand and crack the quartz matrix etc. By removing the useless quartz, they were able to better calculate the true gold weight of the 'nugget'.

It's sad because the Australian Government complained shortly thereafter about how it was such a terrible loss that the Welcome Stranger had been cut into pieces and melted down almost immediately. People often lament the loss of such a wonderful treasure AFTER it has been passed on or destroyed. But note also that the Australian Government recently failed to even bid on the largest recently found nugget "The Hand Of Faith" which was eventually sold to the Golden Nugget Casino (?) in Vegas. Again, they're wringing their hands and complaining that it should have been bought by an Australian museum, yet the nugget was estimated at 5 million and yet sold for about a million and a half so the people who found it could rid themselves of it ASA.

I seem to recall a reference to the gold working of the Africas by the ancient Egyptians.... in that they used slaves to mine the reef gold. The slaves would set fires below the reefs to heat the rock face before pouring vinegar wine down over the matrix from above. The immediate change in temperature would cause explosions in the quartz. Unfortunate miners were sometimes killed or blinded by the shards of quartz as these explosions took place.

As I mentioned earlier, a lot of people selling gold that has been sluiced or dredged seem to be bleaching their gold with acids these days.
I'm finding the Oxalic Acid a little slow for cleaning nuggets though I'm not prepared to consider the risks involved with Hydrofluoric Acid.

Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: dargo
Date: March 12, 2008 04:35AM
Good post as always Nero,thanks for the advice.Dargo.

Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: nero_design
Date: March 12, 2008 06:10AM
Hey Dargo: are you a Farscape fan by any chance?

Bleaching a nugget??:blink:N/T
Posted by: B.T
Date: March 12, 2008 08:33PM

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Re: Cleaning Your Gold Nuggets - Methods & Techniques?
Posted by: dargo
Date: March 13, 2008 04:13AM
Hi Nero,I'm not a Farscape fan,but I checked the website and can see where your coming from.I do a fair bit of detecting in the Victorian high country and I use the name of Dargo as it is a small town near where I prospect.Cheers Dargo.

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