|
Up
| |
Gemstones - Natural gemstones are found in nature. Laboratory-created
stones, as the name implies, are made in a laboratory. These stones, which also
are referred to as laboratory-grown, [name of manufacturer]-created, or
synthetic, have essentially the same chemical, physical and visual properties as
natural gemstones. Laboratory- created stones do not have the rarity of
naturally colored stones and they are less expensive than naturally mined
stones. By contrast, imitation stones look like natural stones in appearance
only, and may be glass, plastic, or less costly stones. Laboratory-created and
imitation stones should be clearly identified as such.
 Gemstones may be measured by weight, size, or both. The basic unit for weighing
gemstones is the carat, which is equal to one-fifth (1/5th) of a gram. Carats
are divided into 100 units, called points. For example, a half-carat gemstone
would weigh .50 carats or 50 points. The carat weight of a gemstone is not an
accurate gauge of its size. Some gemstones have higher density and are therefore
heavier than other stones of the same size. Two gems of the same carat weight
may appear to be different sizes. Because sapphires and rubies (both a form of
the mineral corundum) are denser than emeralds, a 1-carat sapphire or ruby will
be smaller than a 1-carat emerald. A ruby that seems to be the same size as a
diamond will have a different carat weight, because a ruby is denser than a
diamond. When gemstones are measured by dimensions,
the size is expressed in millimeters (for example, 7x5 millimeters).
Gemstone treatments or enhancements refer to the way some gems are treated to
improve their appearance or durability, or even change their color. Many
gemstones are treated in some way. The effects of some treatments may lessen or
change over time and some treated stones may require special care. Some
enhancements also affect the value of a stone, when measured against a
comparable untreated stone.
Jewelers should tell you whether the gemstone you're considering has been
treated when: the treatment is not permanent; the treated stone requires special
care; or the treatment significantly affects the value of the gemstone.
Some common treatments that you may be told about and their effects include:
Heating can lighten, darken or change the color of some gems, or improve a
gemstone's clarity.
Irradiation can add more color to colored diamonds, certain other gemstones and
pearls.
Impregnating some gems with colorless oils, wax or resins makes a variety of
imperfections less visible and can improve the gemstones' clarity and
appearance.
Fracture filling hides cracks or fractures in gems by injecting colorless
plastic or glass into the cracks and improves the gemstones' appearance and
durability.
Diffusion treatment adds color to the surface of colorless gems; the center of
the stone remains colorless.
Dyeing adds color and improves color uniformity in some gemstones and pearls.
Bleaching lightens and whitens some gems, including jade and pearls.
| |
|
