Fine cultured pearls should last for many years, even generations---but only if they are properly cared for.

Cultured pearls should be kept free of perfumes, cosmetics, perspiration and dirt, advises Tiffany & Co. Acid and akali substances can be harmful to pearls, including chemicals found in perfumes, skincare products, hair products and even perspiration due to the salt content. On the other hand, the body's natural oils (apart from heavy perspiration) are actually beneficial for pearls and keeps them from drying out. The issues are the same for colored pearls. A cultured South Sea, Tahitian and golden pearl necklace with a diamond clasp by Tiffany & Co. is seen above.

Tiffany & Co. advises pearl owners to follow the old adage "pearls should be the last thing you put on and the first thing you take off". Avoid getting your pearls wet and don't wear them when bathing.

If your pearls are soiled, clean them by gently wiping the pearls with a slightly damp cloth. Do not use a chemical-based cleaner on them, as they can become damaged.

Do not store your pearls with other pieces of jewelry, as they can be easily scratched. Separate the pearls from other items by keeping them in a soft bag or wrap them in a cloth before storing them.

Tiffany & Co. cultured pearls are strung on pure silk with knots between each cultured pearl. Over time, the silk will stretch, weaken and become soiled. If you wear your cultured pearls regularly, Tiffany's advises having the pearls professionally cleaned and restrung annually. This will prevent the strand from breaking.

Diamonds are among the hardest of all minerals. Still, they require special care to keep them looking their absolute best.

The brilliance of any diamond depends on the amount of light that can enter the stone and reflect back to the human eye. However, the smallest deposit of grease on the surface of a stone can dull its reflection. Even a touch from a finger will leave a smudge of natural oil, according to De Beers, one of the world's leading diamond companies.

Clean your diamonds with a simple mix of six parts water to one part ammonia and apply with a soft, natural bristle brush. If you have no ammonia in the house, you can substitute with a mild liquid detergent. Rinse with fresh water and dry with a soft, non-abrasive cloth. If your diamond has a crack or inclusion, De Beers advises owners not to use ultrasonic cleaners, as the vibrations of the cleaners can enlarge flaws.

A few words of warning. De Beers recommends that jewelry not be cleaned in or near the sink. If there is no better location for the cleaning, be sure the plug is in, to avoid the jewelry going down the drain. If you are using a brush, be gentle: diamonds can work loose from their settings if treated roughly, warns De Beers. If you use hand lotion, wait for at least 10-15 minutes before putting your rings back on, as the ring might easily slip off.

While most people believe that diamonds are impervious to scratches, that simply is not the case. Indeed, another diamond can easily scratch another. To prevent such scratches, separate diamond jewelry in your jewelry box, advises De Beers. Diamonds also can scratch other gems or jewelry, especially soft items like pearls. And even though diamonds are hard, they can be brittle, especially along thin edges. Try not to wear your diamond when it might be struck sharply, and if you have an especially thin cut, keep it protected. If you are traveling, use a secure travel pouch, which will keep individual pieces safely apart, according to De Beers.

De Beers recommends having important pieces of jewelry checked quarterly to be sure the stones are secure in their settings.

Most people know the four "Cs" of diamonds that determine the value of a stone. These are cut, clarity, color and carat weight. But there's a fifth "C" you should not overlook, which is the diamond certificate. The diamond certificate---sometimes called a grading report---is a complete evaluation of your diamond that has been performed by a qualified professional with the help of special gemological instruments. Each stone bears its own recognizable, individual characteristics, which are listed on the certificate. Be wary of investing in a diamond without one.