When I shop at the jade markets in China, the shops that have the best quality jade are kept dark. The cases the jade are in have lights that turn off between customers viewing. If the weather is hot, they often have fans blowing on them. And there are bowls of water in the glass cases to provide moisture. One of the methods for adding more color to gemstones is exposing it to heat.
I put my jade bangle on my wrist even though it felt warm, and amazingly I could still feel the coolness of the jade stone. Grade A jadeite cools quickly. It appeared more green for awhile, but it often appears more green as I'm wearing it especially when the weather is hot. Also, when I'm doing tai chi, yoga, my jade looks more vibrant, and glows from the qi energy, but that's a natural happening. You may notice in some of the descriptions that jade will look more pretty as you wear it, and that's because of your body qi energy. One of the reasons jade is so popular for centuries in China is because of the jade relation to body qi, and how the jade qi helps to balance the body. You might get your jade bangle "all qi'd up", take it off and put it in a drawer, then weeks later when you get it, you have to look twice because it does lose the "glow" of your body qi when it's not worn.
But, what does it mean when your jade turns black? If you take care of your jade, and it's good quality and natural color, it won't turn black. In fact, true black is not a jade color. It might be charcoal color, or deep deep green that looks black, but when you hold it to the light you can see some green hues around the edges. That's a method to check to know if your "black" jade is genuine jadeite or Chinese jade.
Exposing jade to sunlight and heat for extended period of time may cause the color to change. If you put your jade bangle in a drawer for several months, and it gets warm and dry, the jade stone gets compromised. Wearing jade in chlorine water, for cleaning or swimming, may also affect the color. Some Chinese jade sellers take good jade and bury it in the ground for months to make it look "antique" because of the way the color changes.
Jadeite that has been bleached with acid to remove undesirable poor color, then treated with polymer or other coloring may eventually turn black because the acid will destroy the
jade stone. More often, the acid and color treated jade loses its color. When I'm not sure jade that was sold to me is really natural color, I keep it in storage, under the proper conditions, for 5 years or more prior to listing, and if the color remained stable, then it's probably the natural jade that is it supposed to be.
Chinese people and Chinese healers often believe that if you are very ill and have disease, or if the person wearing the jade is an evil person, the "bad qi" of the body will cause the jade to change color. I tend to believe that, because when I had an illness that required a very powerful medicine that made me miserable, my jade bangle didn't look as good as it usually does.
Sometimes when I question a person whose jade bangle got black, or changed color, I learn that they bought their jade in a Chinatown. I have been to many Chinatowns all over the world, and it's very rare to find the jade bangles in a seller's shop kept in the proper conditions. They are often kept on glass shelves under strong light, air conditioning making the air very dry to dry out the jade stone. And they are often handled roughly, not individually cased in a box which means they get chips, scratches and get worn out before it's even sold. If you see the jade bangles kept in these kind of conditions in a Chinatown, don't expect the seller to really know about jade. Just because a jade seller is Chinese doesn't mean they know "all about jade"!
So there could be many reasons why your jade turns color. Find out how the jade was cared for and stored before you purchased it. And although it's not easy to know the truth about your jade without a gemology testing, it could be something other than jade, or poorly color treated.
Buy from a trusted jade seller. Our best jade bangle bracelets and other jade is listed on the Jade Heaven web site. Most of it is vintage, mined prior to the year 2000. It is stored in dark, cool and moist conditions. And most of it has been purchase many years before it is actually listed, to make sure there is no color change.
If you do want natural "black" jade, especially jade bangle bracelets, our Chinese jade, and the carved "Dynasty" Chinese jade bangle bracelets on Ying Yu Jade are the best quality you can buy anywhere.