Can You Get Mercury Out of Gold?
Q: My 22 karat gold wedding ring became discolored after coming into contact with mercury from a broken thermometer. Is it destroyed, or can it be fixed?
A: First off, don’t wear the ring till the mercury has been removed. The stuff is pretty damned toxic. Second, please, please, try to avoid using and/or breaking mercury-filled thermometers. In most applications, there are safer alternatives. If you do need to use a mercury-filled one, for heavens sake, be careful. If you do break one, it’s imperative that you take great pains to clean up all the spilled mercury. Even small amounts, trapped in, say, your carpet, will slowly evaporate, and if the room has poor ventilation, you can be getting low levels of mercury exposure over time, which is not good at all.
I recently read an interesting, tragic, and scary article about a researcher on the East Coast who’d been exposed to a single drop of methylmercury which spilled and contacted her latex lab glove. Now, this stuff is far, far, more toxic and absorbable than metallic mercury. But that single drop, which she’d immediately washed off, apparently absorbed right through her glove and contaminated her enough that 9 months later, she was dead from it, despite medical science’s best efforts to save her. Again, this stuff was much worse than metallic mercury, but the mercury in that compound was the toxic agent. The chemical form simply enhanced the ability of her body to absorb it.
The lesson here is that mercury is scary stuff. Don’t take chances with even small amounts of fumes or exposures.
Now to your actual question. Removal of the mercury is possible. The common method is by heating the gold item hot enough to vaporize the mercury. This is a “low red” heat, similar to what is used in annealing the gold. The result is that the gold is again safe to wear, although it may require some re-polishing after this is done. The mercury may also, if it has not been allowed to penetrate deeply into the gold, be removed by acid dissolution. But however it’s done, it’s imperative that the goldsmith take great care not to breathe the fumes generated by heating or other methods. The mercury fumes are much worse than a little mercury on the ring, as it would then be absorbed into the lungs if breathed.
This is not a danger to take lightly. Properly, the procedure should be carried out in a fume hood, specifically one equipped to scrub the mercury from the exhaust before releasing it into the atmosphere. Obviously, this isn’t common equipment in a jewelry shop. At the very least, it should be done outside, with a breeze to carry the fumes away. This process is quite similar in nature to the historical processes used in gilding—the process used for covering silver items with thin layers of gold, prior to the development of electroplating, and to the processes often still used to recover gold from crushed ore. In both cases, people involved in these processes tend to have drastically shortened lives and rather unpleasant deaths.
by Peter W. Rowe M.F.A., G.G.