[Jewelry making - Article 00135] - [Orchid] Opal - Water filled with fire

[Sandra I. Smith]

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    The fragile opal first flashed its fiery colors at mortals millennia
    ago, igniting a love affair that has survived the fickleness of the
    human heart. Its faults, like softness and lack of stability, are
    overlooked by those entranced by its beauty. 

    Although comprised simply of silica and water, opal is one of the
    most complex gemstones known. Not only are opals unique among the
    members of the mineral family, no two opals are identical. The
    molecules in most gemstones form crystals, but the silica molecules
    in opals take the shape of tiny spheres. The silica spheres pack
    together tightly in precise layers. Although the spheres and layers
    are as close to each other as they can get, tiny spaces between them
    exist. Opal's uniqueness results from the minute differences in the
    sizes of the silica spheres and their spacing from one another. 

    The play of color, or fire, prized so highly in precious opal, is a
    special effect of light. All color comes from light, which may be
    absorbed or reflected back from solid substances like gemstones. The
    absorbed colors, "bouncing" around the silica spheres and the spaces
    between them, produce a brilliant play of color as light moves
    across an opal's surface. 

    Each type of color is named according to its appearance. Large
    square-shaped patches of color are called harlequin or mosaic. Flash
    fire describes large irregular patches of color. Flame fire is
    streaks of color, while pin fire refers to small pinpoints of color.
    Sheets of color that roll across the surface as the stone is moved
    are called rolling fire. Broad flash fire is sheets of color that
    cover the stone. Other descriptive names include zebra, Chinese
    writing, and straw. These latter varieties are rarely found. 

    Opal that doesn't have a play of color is called common opal or
    potch. Water, or jelly, opal is transparent, without a play of
    color, but has an iridescent glow that makes it desirable. 

    Gilson opal is a synthetic (manmade) which mimics all the chemical
    and physical properties of genuine opal. Slocum stones are imitation
    opals made from glass. Both glass and plastic imitations have been
    named Opal Essence. Opalite is made from plastic. Many of the
    imitations duplicate the play of colors so skillfully that they are
    difficult to distinguish from precious opal with the naked eye. 

    Although nearly all precious opal today comes from Australian mines,
    opal is found throughout the world. Within the United States, opal
    has been located in Arizona, Oregon, Idaho, and Nevada. Prior to the
    discovery of Australian opal, the Czerwenitza area of what was
    formerly known as Hungary was the major source of opal. Although the
    area has been renamed as political circumstances change, opal from
    the Czerwenitza mines is still known as Hungarian opal. Mexican fire
    opal contains iron, which gives it a distinctive red/orange color.
    It does not have the play of color that other opals have. Color
    descriptions in opal usually refer to the background, or base,
    color. That's the color seen when looking straight down at the opal.
    Although opal is found in a variety of colors, including yellow and
    blue, black is most highly prized base color. Additionally, opal may
    range from transparent to opaque. Their names indicate the opals'
    color and translucency. A black opal is opaque, with the play of
    color showing against a dark background. Black crystal opal is the
    same as black opal, except it is transparent or translucent. White
    opal displays its play of color against an opaque white background. 

    The name opal comes from upala, which is Sanskrit for stone. Opal
    has been valued since ancient times, its first use being to protect
    the wearer from diseases, particularly those of the eye. Opal was
    especially popular in the Middle Ages, when it was thought to make a
    person invisible. Negative superstitions later linked opal with
    death and bad luck. It didn't regain its popularity until Queen
    Victoria made it a Court favorite. Opal's fragility, as well as
    superstition, has contributed to its fluctuating popularity. 

    Opal is formed when ground water leaches silica from the soil. The
    groundwater accumulates in cracks deep within the earth where most
    of water eventually evaporates, leaving the silica behind. After 15
    million years or so, natural forces such as heat solidify the silica
    into opal. When mined, opal may contain up to 20 percent water,
    which continues to evaporate over the life of the opal. To
    counteract that evaporation, opal needs to be dipped in pure water
    frequently to keep it from dehydrating. If it gets too dried out, it
    will develop a network of fine surface lines (craze), and possibly
    crack. Because of its water content, extreme temperatures can cause
    opal to break. Opal is also soft and quickly scratched. Opals crack
    easily during polishing or from the pressure of being mounted in a
    setting. 

    Opal is very absorbent. It should never be cleaned with anything but
    pure water, because it will absorb anything, including other
    minerals, in the water. Putting an opal in an ultrasonic cleaner
    will destroy it. Hair sprays, perfumes, and cosmetics should be
    applied before putting on opal jewelry. Opals need to breathe and
    should not be stored in plastic bags. Wrapping them in soft cloth or
    leather both protects them and allows the fresh air they require. 

    Because of their fragility, opals are often sold as triplets or
    doublets. An opal triplet consists of a piece of precious opal
    sandwiched between a top layer of clear quartz or glass and a bottom
    layer of common opal. A doublet is usually precious opal underneath
    a quartz layer. The quartz primarily protects the soft opal from
    scratches. The layers are usually fused together with a colorless
    cement. 

    Opal--unique among gemstones. Fragile, but fascinating. Made of
    water, but filled with fire. Its brilliant beauty overcoming its
    faults, the fiery opal enchants with its dazzling display of color.
    Its special place in the human heart is secure. 



****Sandra I. Smith, Writer ****

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