TOEFL reading material

[hera]

GEMSTONE PROCESSING
The processing of the mine run involves different operations, depending on the quality of raw materials and the areas from where they have been mined. These processes may include: high pressure water washing, hammering, sawing, forming, calibrating, faceting and polishing.
Quality control in every stage of the processing is strictly practiced, these procedures assure that every gemstone produced is absolutely flawless.

General Enhancement Categories:

Specific Enhancement
Bleaching - Use of chemicals to lighten or remove a gem's color
Coating - Use of surface treatments such as films, lacquers, etc. to provide color or other special effects
Dyeing - The introduction of coloring matter into a gem to give it a new color or greater
intensity
Filling - Incorporation of colorless borax or other substances into cracks as a by-product of
heating the stone, used only if such material is visible at 10x.
Gamma/Electron Radiation - The use of gamma or electron irradiation for the purpose of
changing a gem's color, may be followed by a heating process to stabilize the color. Such
stones do not exhibit residual radioactivity.
Heating - The use of heat to clarify, change color or create phenomena in gems. Any filler
materials, which enter the gem, as a result must not be visible in fractures at 10x.
Infilling - The intentional filling of surface breaking cracks and cavities with a foreign material
such as synthetic resins with hardeners (Opticon), glass or plastic.
Lasering - The use of a laser to drill into a stone and remove or alter an inclusion, refers
specifically to diamonds
Oiling or Resin Infusion - The intentional filling of surface breaking cavities and cracks in
transparent or translucent gems with a colorless oil, wax, resin or man-made unhardened resin.
Irradiation - The use of neutron bombardment to alter color. This process creates residual radioactivity and such stones must receive a Nuclear Regulatory Commission safety release prior to sale. Usually used in combination with other radiation and or heating treatments.
Bonding - The intentional use of a colorless bonding agent (usually plastic) within a porous gemstone.
Diffusion - The use of specific chemicals during a high temperature heating process for the purpose of penetrating the surface layer (usually to a slight depth only) with coloring or star-making chemicals. Such treatment is not generally accepted and stones sold with this enhancement must be specifically labeled as diffused.
Waxing/Oiling - The impregnation of colorless wax, oil or paraffin into porous opaque gems to improve appearance.

Q & A
Q. What are the main reasons for changing a natural gemstone?
A. Many gemstones are enhanced, which may improve or change the color, provide stability, or increase durability. Stability means that the stone won't change under normal conditions. Turquoise is an unstable gemstone in its natural state, because chemicals and body oils easily damage it. Durable stones won't scratch or break when worn. Soft stones, like opal, must be protected if they are to last.
Q. How are gemstones changed?
A. The four main methods of enhancement are heat treatment, irradiation, chemical treatment, and assembly. While some enhancements are done with an intent to deceive, many gemstones would not be usable in jewelry if they were not treated in some way. Reputable suppliers disclose known enhancements at the time of purchase.
Q. How can we tell?
A. Their name is often a clue to substitutions. Genuine gemstones are called by their true names, with no descriptive words as part of the name.
Example, a sapphire is simply called a sapphire. However, a water sapphire is iolite or cordierite. A balas ruby is spinel. A Madeira topaz is citrine. Evening emerald may be any green stone. German lapis is dyed chalcedony. Mexican jade is dyed onyx. Herkimer diamonds are quartz.
New names are invented on a regular basis. As a consumer, you need to be aware that gemstones with additional names are substitutes and pay the appropriate price or them.
Q. What is a natural gemstone?
A. Suppliers may only call gemstones natural if nothing has been done to them which changes their color, stability, or durability. Natural gemstones may only be polished or cut to show off their beauty. Natural stones often have imperfections in them. Perfect gemstones are a tip-off to experts that a human has improved upon Mother Nature.
Q. How can we tell the difference between a natural and an "enhanced" (treated) gemstone?
A. It is usually impossible to detect which gemstones have been enhanced by either of these methods. Chemical enhancements are generally used to change the surface characteristics of gemstones, and assembly is often used to protect fragile stones.
Assembly is usually easy to detect before a stone is set; the results of chemical treatments range from obvious to invisible.
Q. What is heat treatment?
A. Heat treatment is commonly used to improve color. Color changes resulting from heating are permanent in most gemstones.
Amethyst, ruby, sapphire, topaz, tourmaline, and zircon all are routinely heat-treated. Most aquamarine now sold has been heated, to change it from its natural green to the blue that is currently popular.
Q. What about irradiation?
A. Irradiation is also used to change or deepen gemstone colors. Clear topaz is irradiated to produce blue topaz, and colorless tourmaline may be changed to any one of several colors. Some diamonds are irradiated to improve their color.
Irradiation is not always permanent; some irradiated stones revert to their natural colors when exposed to extreme heat or light.
Q. What does chemical treatment do?
A. Chemical treatment of gemstones includes bleaching, dyeing, and staining. It also includes the uses of oils, waxes, resins, or plastics to stabilize or change the appearance of a gemstone. Chemical treatments are often called impregnation because the chemicals usually penetrate the surface of the stone. Porous stones, like turquoise, are frequently sealed with wax or resin to keep the color from fading. Oils, waxes, and plastics are used on many stones to hide small scratches and surface flaws. Coral, ivory, and pearls may be bleached. Nearly all gemstones can be dyed or stained. Some chemical treatments are permanent. Others will dissolve in solvents like acetone or in ultrasound cleaners. Waxes melt when exposed to heat or strong light. Bleaching can be impossible to detect. Dyeing can usually be detected with a microscope.
Q. What does "assembly" mean?
A. Assembled stones may be composites like doublets and triplets, or they may be foilbacks. A composite stone is two or three pieces of material fused or joined by colorless cement. Although any stone may be made into a composite, opals are the best-known. An opal triplet consists of a piece of good opal sandwiched between a top layer of clear quartz and a bottom layer of low-quality opal. A doublet is usually a good opal underneath a quartz layer. The quartz helps protect the delicate opal. Composites also allow the use of gemstones too small to be used otherwise. False composites contain no gemstone material. False opal doublets are made from crystal cemented over abalone shell. Soude emeralds are crystal cemented over green glass.
Q. What does foilback mean?
A. Foilbacks have been made for nearly 4,000 years, using a variety of techniques. One kind of foilback involves placing a backing of foil or a metallic coating on a stone to give it a more brilliant color. Colored substances on foilbacks add color to clear stones or deepen the color of pale stones. Cat's-eyes and star effects are created with etched backings. Rhinestones are one example of a popular foilback.
Q. Are pearls synthetic or natural?
A. Cultured pearls fall into a special category. Natural pearls are made by mollusks (oysters and mussels). Mollusks have shells and most of them live underwater. They secrete a substance called nacre (rhymes with acre). The purpose of nacre is to make the inside of the shell smooth so that it doesn't irritate the soft body of the mollusk.
A pearl is simply an abnormal growth of nacre. Natural pearls are formed when something, such as a grain of sand, gets inside its shell and irritates the mollusk. To reduce the irritation, the animal covers it with thousands of smooth layers of nacre. The process is similar to what your body does when it forms a callus to protect irritated skin.
The difference between cultured and natural is in how the pearl is started. A cultured pearl is formed around an irritant placed in the oyster by humans, rather than around a grain of sand randomly lodged in the oyster by nature.
The outsides of natural and cultured pearls have an identical appearance. It generally takes an expert and special x-ray equipment to distinguish cultured from natural.
Cultured pearls may not be sold as natural; however, they are regarded as "real" pearls and not fakes. Nearly all pearls on the market today are from Japan. There are also many pearl companies in Hong Kong. Freshwater pearls are also produced in the United States. In Tahiti, the famous black pearls are cultured.

LIST OF GEMSTONES AND THEIR COMMON ENHANCEMENTS
Agate: can be dyed
Amethyst: Not always treated. If treated, heat treatment can lighten the color. Can also be produced by irradiating citrine to turn it from yellow to purple.
Aquamarine: heat treatment can change green material to blue.
Carnelian: can occasionally be dyed; heat treatment can improve color.
Citrine: Not always treated. If treated, can be produced by heat treating amethyst to change color from purple to yellow.
Diamond: Colorless diamonds are generally untreated. However, they can be laser drilled, the impurities bleached, and then fracture filled to improve clarity. Light yellow and brown diamonds can be irradiated to change color to green, brown, blue, yellow, orange, and more rarely, pinks and reds.
Diopside: no known treatments.
Emerald: Traditionally, for hundreds of years, almost all emeralds have been treated by soaking in oil to improve appearance. The oil penetrates the surface reaching fractures and makes them appear less noticeable. It can also help to increase color saturation. Today, while still routine, this practice has taken on a more advanced level. Instead of oil, emeralds are commonly treated with a high-grade epoxy resin, such as Opticon (registered), to improve their appearance and increase durability. The 5.76 carat emerald featured on the "Green with Envy" page has been treated in this more advanced fashion. These treatments are not permanent and can all be reversed. Because it is well known that all emeralds are treated, this has virtually no effect on value.
Garnet: no known treatments.
Iolite: no known treatments.
Jade (both jadeite and nephrite): can be bleached, dyed, polymer impregnated, or heat treated- or a combination of these. The trade typically refers to three types of jadeite: 'A' jade, 'B' jade, and 'C' jade.
· 'C' jade is the most common type of jade and accounts for most jade found in jewelry. It is usually bleached, dyed, and polymer impregnated.
· 'B' jade is a natural color jade that has been bleached to remove any dark, unattractive discolored areas. It is also often polymer impregnated (which increases the durability of this already tough gem material).
· 'A' Jade is completely untreated in every way and is both very rare and expensive.
Kunzite: can be (but very uncommonly) irradiated
Kunzite Note: Unrelated to enhancement--Exposure to intense sunlight over a very long period can cause the gradual fading of this pink gem.
Lapis: commonly dyed and polymer impregnated or oiled to improve color and luster.
Malachite: very uncommonly impregnated with a polymer/epoxy resin.
Moonstone: no known treatments.
Opal: I use untreated opals and occasionally opal doublets. Opal doublets are an assembled stone that combines, via epoxy, a thin layer of opal backed by either chalcedony or boulder rock.
Pearl: Routinely bleached to remove discoloration. White pearls are dyed to achieve a pink overtone (rose overtone). While some pearls are dyed to change color completely, most dark colored Chinese pearls are irradiated to change their color. The pastel colors of Chinese freshwater pearls are supposedly untreated and therefore of natural color.
Pearl note: Mabe pearl: Mabe pearls are cultured 'blister pearls.' In the culturing process, instead of inserting a bead nucleus 'free-floating' into a mollusk or oyster to get a round-shaped pearl, the nucleus is attached to the inner lining of the shell. The mollusk then begins to 'cover' this irritant with calcium carbonate, composed of calcite and aragonite, the two minerals that make up the pearly nacre of a pearl. When the mollusk is harvested, the pearl that has formed like a blister on the inner shell is cut out and backed with mother of pearl or shell.
Pearl note: Keshi pearls: Keshi pearls are entirely untreated. After being removed from the mollusks, they are washed only with a gentle soap and rinsed with water.
Peridot: no known treatments.
Rock Crystal Quartz: no known treatments.
Ruby: can be heat treated, diffusion-treated (I do not sell), and occasionally oiled and dyed (I do not sell).
Sapphire:
Blue sapphire--can be heat-treated or diffusion treated (I do not sell)
Yellow/Orange Sapphire--irradiated.
Smoky Quartz: usually natural; very black material is usually irradiated.
Tanzanite: routinely heat-treated.
Topaz:
Blue: irradiated followed by heat treatment.
Pink: heat-treated.
Tourmaline:
Pinks & Reds: commonly irradiated.
Greens: often heat-treated.
Turquoise: can be polymer impregnated
Note: Turquoise is often reconstituted, and this can be hard to detect. Reconstituted turquoise involves grinding up pieces of turquoise, pressing them into solid pieces with an adhesive binder such as an epoxy, and then recutting.