Perspiration, which is essentially rich in sodium chloride (common salt), can cause gold jewelry to tarnish. However, it is not as susceptible to tarnishing as other metals with a lower carat weight, such as 14k. This is because it contains a higher percentage of pure gold (which never tarnishes, corrodes or rusts). Gold doesn't tarnish and lasts forever, but the other metals in the alloy will tarnish.
However, 9-carat gold is vulnerable to serious tarnishing, especially if it is alloyed with copper, and sometimes turns green or black. The other metals in 9-carat jewelry can also react with the wearer's skin (especially if nickel is present) and sometimes cause dermatitis. Any gold jewelry will also darken if it has been frequently exposed to the use of soap or lotion. It is this addition of metals that hardens the texture of gold and therefore makes the jewelry durable.
Since gold is more expensive than copper and silver, the higher the percentage of pure gold a jewel has, the more expensive it will be: 22-carat gold jewelry is the most expensive. To clean a gold jewel that has turned black, you must first cover a medium bowl with a sheet of aluminum foil. Since this is the most gentle form of gold jewelry for retailers, you should take care of them so that they don't wear out from overuse. Any piece of jewelry made of pure gold will not tarnish at all because it would never corrode or rust.
You often see Olympic athletes chewing on their gold medals, because, traditionally, if you could make marks on your teeth on soft metal, you knew that it was authentic and very similar to pure, even though modern Olympic medals are not made of solid gold. If you happen to wear your 22-carat gold in the water, make sure to rinse it off with fresh water as soon as possible. Sometimes, the real cause of jewelry turning black is due to careless maintenance, which is very necessary for gold jewelry. In fact, 22-carat gold jewelry is a more popular choice because it's more durable and less likely to get scratched.
Any type of hard metal can easily change the actual color of gold, while plating can also discolor. In addition, 14-carat gold is harder and more durable than 22-carat gold, making it more resistant to scratches and everyday wear and tear. The main difference between 14k and 22-carat gold is that 14k gold contains 58.3% pure gold, while 22-carat gold contains 91.7% pure gold. One of the most likely reasons why gold turns black is due to metal abrasion or poor quality coating and corrosion.