If you wear jewelry, I'm sure you know that it requires frequent care and cleaning. It does not take much to diminish the appearance of the gemstones in your jewelry, and if you want to keep them looking great you need to know what to avoid, and how to clean them when they need it.
Some jewelry care is simply a matter of common sense. Try to avoid any hard impact to the jewelry or gemstones. Sometimes an accidental whack on something hard like the kitchen counter is enough to knock a stone loose, or worse, break the stone(Especially if it is a stone easy to break like an emerald.)
Avoid getting oils and lotions on your jewelry. The most common things that make your jewelry lose its sparkle are oils and liquids that are on the stone. Even the natural oils from your hands in the form of fingerprints can easily affect the beauty of your stones. Heavier amounts of oils can almost make the stone look completely lifeless, because they change the way light passes through the stone and greatly affect the appearance of the jewelry. Simply hand tossing a salad with oil and vinegar dressing on it is often more than enough to greatly change the appearance of your stones. Take your rings off before doing anything like that. Also remove your rings before applying any lotion to your hands. Its great for your skin, but not so good for the appearance of your jewelry.
Avoid sudden and extreme temperature changes whenever possible. Don't leave your jewelry on the dash of your car on a hot summer day, or do anything that may introduce high temperatures, or sudden temperature changes. Some gemstones will tolerate heat better than others, but in general it is a good idea to "play it safe" with all of your jewelry. Sometimes with very heat sensitive stones, even reaching into a hot oven to get something out causes enough of a temperature shock to make the stone change color, or crack.
Avoid harsh chemicals when wearing your jewelry. Some stones can be affected by chemicals, or acids, and it will greatly diminish the beauty of your stone. Peridot is one good example of a stone that can be damaged by chemicals or acids(even common acids like vinegar.) Take a look at a "well worn" Peridot ring. If it has not been properly treated, the stone will often have a frosted appearance caused by chemicals slowly etching the surface of the stone over repeated exposures during years of wear. This is not damage you will typically see after one exposure, but in time it will eventually make the stone resemble a piece of beach glass instead of a beautifully faceted gem.
There are several ways you can clean your jewelry and gemstones. Keep my earlier advice in mind when cleaning your jewelry. Don't drop your cold jewelry straight into boiling water or you could damage your gemstones.
The first cleaning method I will talk about here is the method I would recommended for most jewelry, Especially if you do not know what the stone is, or it is a stone that is easy to damage. This method is probably the most gentle method, and is safe for almost all stones if you use caution. Just get a clean soft bristle tooth brush and some warm soapy water. let the jewelry soak for a few minutes to loosen up any caked on or dried up dirt, then lightly scrub it with the brush. Take care to clean all around the stone, and behind it as much as possible. Sometimes the back of the setting is open and you can get the brush in there from that side, and sometimes you can only try to get a few bristles in between the prongs to get under the stone. Be careful not to use any abrasive cleaners, and just take your time and try to get everything cleaned out as good as possible. Rinse it off in clean water and it'll look like new again. With stones that have been filled with an oil or resin(like most emeralds) you may want to try just water so you don't wash the oil out with the soap.
The next method I want to mention here is the use of an ultrasonic cleaner. An ultrasonic cleaner sends very high frequency sound waves through a cleaning solution producing millions of microscopic bubbles to form wherever the cleaning solution contacts something. These tiny bubbles will scrub the dirt our of even the smallest hard to reach areas. This can sometimes be a very good, very easy way to clean your jewelry, but it can also sometimes damage stones. There are very powerful professional units out there that can cause serious damage to some stones in a matter of seconds, and there are more common "home" units which can usually be purchased for less than $100. The smaller home units are much less powerful, but still do a good job with a little more time. Even the home units can damage some stones, so be careful if you plan to use one of these. Many of the more durable stones like Diamonds, sapphire, rubies, garnets, and members of the quartz family are usually safe in an ultrasonic cleaner, but avoid using ultrasonic cleaners on any stones that have inclusions, fractures, or fractures that have been filled. These stones could be damaged by the ultrasonic cleaner.
The third method commonly used for cleaning jewelry is steam cleaning. This can work very well to loosen up dirt and oils and will really clean jewelry up nice, and fast. It is not safe to use steam cleaners on all gemstones though, Especially stones that are heat sensitive. Again, make sure the stones you want to clean will tolerate steam cleaning before attempting it. In general, do not steam clean a stone unless it is also safe to use an ultrasonic cleaner.