(If you know how to avoid the effects of corrosives on gold)
Recently, a co-worker commented on a news story about the discovery of some ancient seafaring vessel that was found to contain gold coins of the period. He remarked that the coins, after being submerged in seawater for hundreds of years, looked brand new when brought to the surface and the debris removed. The rest of the ship (both wood and metal) had deteriorated to the extent that identification was going to be a tedious process. Not so with the coins, whose markings were as crisp as the day that the ship went down. How could that be?
All in all, it was a testament to the corrosion-resistant property of gold, our most valued metal.
Gold has many unique properties that, along with being visually appealing, have made it a highly valued commodity since its discovery about 6,500 years ago. There are few people who do not recognize gold for its use in jewelry. Perhaps in some “lost world” scenario, there is a group of indigenous people who were not exposed to the beauty of gold until some explorers (or tourists) let them see it, but that would be a great exception.
It is more likely that many people are unaware of gold’s other attributes. For example, gold is the most malleable of metals, which means it can be hammered or flattened into a sheet thin enough as to be slightly transparent (with a green tint). This allows it to be used as a coating on everything from glass (as in astronauts’ face shields to negate the effects of ultraviolet rays) to an edible layer on a $1,000 piece of chocolate cake.
Gold is also one of the most ductile metals, with an unsurpassed stretching capability. One ounce of gold can be stretched into a wire almost 50 miles long! Gold is a great conductor of electricity on its own or can be used to coat other metals, such as copper, which on their own would tarnish and corrode.
By the way, copper, along with gold, are the only two naturally occurring metals that have a color. All others have a silver-gray look. Which brings me to the heart of this blog—gold’s unequaled resistance to chemical and natural change and what we might do to challenge that resistance by act or accident.
Gold Corrosion and Jewelry
Pure gold has few enemies. Cyanide is one, which is used industrially in the extraction process. Also a mixture of nitric and hydrochloric acid, known as ‘Aqua Regia’ or royal water, will dissolve gold. In the jewelry and pawn business, we use a mixture containing this acid every day when testing the various items brought into our shops.
Mercury is used as a way to extract gold from surrounding material by forming a bond or ‘amalgam’ with gold. My first exposure to this type of reaction came from a nurse friend of mine who was working in a hospital. Some of the night shifts could be long and boring, so she and her co-workers would invent diversions to the tedium. One of the silly things they did was to break open thermometers and let the mercury spill out onto the counter. They would play with the little liquid silvery beads, pushing the liquid apart, and then herding it back together like a scene out of Terminator 2.
Then one of them noticed that their yellow gold rings had turned grey in some sections. Off to the jeweler for help. Unfortunately, in this instance, there was nothing we could do to remedy the effect of gold corrosion on jewelry. Polishing the gold was not going to remove this stain. You see, mercury bonds with the gold, forming a new metal combination. The gold becomes soft and brittle as the mercury continues to creep through the gold.
The only solution is…well there is no solution. You have to replace the metal. In this case, it was an expensive resetting of all her stones into new mountings. What my nursing friends didn’t realize is that handling mercury can be toxic. Ruined jewelry might have been the least of their concerns.
Most of us will never come into contact with mercury, but there is a household chemical that is almost as corrosive—BLEACH! Many a ring has been brought into a jewelry or pawn shop, brown and discolored after someone’s hard day of spring cleaning.
You see, even though pure gold resists almost all common chemicals, your jewelry is not pure gold. Pure gold is listed as 24 karat. The gold you wear is generally 18, 14 or even 10 karat, which means that they are alloys of gold and contain other metals such as silver or copper. The lower the karat, the higher the addition of other metals, which is done to create a metal more suitable for jewelry manufacture (and is cheaper, too).
The bleach will react to these metals so much that, beyond the initial discoloration, the bleach will start to break down the gold jewelry. Of course, the thinner sections, like prongs that hold your diamonds, are the first to go.
A more subtle—but just as harmful—chemical is the chlorine used in swimming pools or the chlorine and bromine found in hot tubs and Jacuzzis. People who spend a lot of time in pools and hot tubs will notice that, over time, their jewelry will start to darken and brown, initially discoloring at any solder joints. Although this discoloration can be polished off by your jeweler (polishing removes a very fine surface layer), continual polishing will thin the jewelry, and will add to the damage done to the metal by the chlorine.
So, please remove your gold jewelry before using any cleaning products that contain bleach or spending any serious time in a pool or hot tub.
Maybe my next blog will be about things you can do to prevent losing your jewelry by forgetting it poolside or sink side. That’s not the way we like to achieve repeat business.