Gold prospectors often ask me “What the best way to clean gold nuggets?” Sometimes nuggets that come out of rivers are bright and polished requiring no cleaning at all, but nuggets that are dug out of the ground are often caked with various different muck, dirt, caliche, ironstone, and staining which will hide the beauty of the gold hidden underneath. On these nuggets, some type of cleaning will often enhance the nugget, both in its visual appeal and with its overall value to collectors as well.
I have heard dozens of different techniques that prospectors have used, and I am sure that all of them work to a certain degree. Most involve soaking in some type of household cleaner. My recommendation would be to use the gentlest method that will get the job done. On some nuggets, just a simple scrubbing with a toothbrush and soapy water will do the trick. On other nuggets, a little more may be required to get the job done.
Any recently dug nugget is probably going to have some dirt and grime stuck to it. Soaking the nugget for 20 minutes in some hot soapy water may be all that is needed to break up some of the grime that clings to them. If you remove the nugget from the hot water and you see some improvement, gently scrub it with a toothbrush and put it back in the water to soak for a few more minutes. Repeating this process may be all that is needed to clean up some nugget for display.
An ultrasonic cleaner can also work wonders to break up the grime that is stuck to nuggets. These are typically used to clean jewelry, and can be purchased for a very reasonable cost. Adding a jewelry cleaning solution can help with the process. There is also a cleaning product called Simple Green that does an excellent job when diluted with water in the ultrasonic cleanser. I have found that this method will work for the majority of dirty gold nuggets, and it does a fine job of removing the grime without giving the nuggets an unnaturally clean look.
Another great way to clean up dirty nuggets is to use vinegar and salt. Using a small glass vial, fill it part way with vinegar and add enough salt that you can see the salt accumulate at the bottom of the vial. Drop a few nuggets in the vial and shake it every once in a while. The rough salt works as a slight abrasive to scrub the nuggets, and the vinegar helps to break up some of the grime and stains. Leave the nuggets in the bottle for a few days or even a couple weeks, giving the mixture a good shake every once in a while. You will notice that the vinegar will take on a stained color, indicating that the grime is being removed from the nugget.
Sometimes hard caliche and ironstone material will be very stubborn, and can be difficult to remove from nuggets. This is where some type of cleaner or mild acid might be needed to clean up the nuggets. Most rust removers that are in the household section of any department store will do the job. One product that was recommended to me several years ago is a rust remover called Whink Rust Stain Remover. It does a fine job of breaking up tough iron deposits. CLR is another well-known product that can get the job done on some of the more stubborn nuggets. I generally try to avoid using harsh chemicals unless necessary, as I find that they can take away some of the natural look of the nugget by actually making the nuggets look too shiny. This is why I would recommend using the gentle soap water scrub if possible, and hold off on using any chemicals until you have determined whether or not they are really necessary.
A method that is used by some prospectors to clean their nuggets is soaking them in hydrofluoric acid. This is an extremely dangerous acid that will remove any and all material that is attached to a nugget including quartz rock. Often high-grade specimens with intricate crystalline gold are etched with acid to expose the gold. The most common use for this is on gold in quartz specimens where the gold is contained within quartz and needs to be completely removed to expose the gold.
Hydrofluoric acid is extremely dangerous; in fact just a few drops can cause serious burns and can even be fatal if it comes in direct contact with the skin. I personally will not get near the stuff, and would not recommend it as a way to clean nuggets. There are much safer ways to clean nuggets as previously mentioned in this article, and hydrofluoric acid is overkill for most jobs. If you have a specimen that you are dead set on using acid to clean, I would strongly recommend finding a professional to do the job, as just a few drops on your skin will ruin your day. Search the internet for pictures of hydrofluoric acid burns and you will see why I recommend avoiding it.
As mentioned earlier, I recommend doing a light cleaning on most gold nugget, and try to avoid the chemicals unless needed. Many nuggets will clean up nicely with a light soak and scrub.