[Jewelry making - Article 00120] - [Orchid] Special Reflections or how gemstones get their colors

[Sandra I. Smith]

========[ Invite a Friend - http://www.ganoksin.com/invite.htm  ]========


    My cats like to participate in most of my activities. Their
    "assistance" generally involves batting supplies off my desk. When
    they sit and stare at me, it's easy to see how one of my favorite
    gemstones, cat's-eye chrysoberyl, got its name. The stone is the
    same golden-honey color as my cats' eyes, and the long, narrow band
    of light across the middle of it looks like their narrowed pupils. 

    Cat's-eyes and star-stones are popular names for the special effects
    caused by light reflections in certain gemstones. They can usually
    only be seen when the gemstone is cut in a rounded or domed shape
    (cabochon). The reflections that cause cat's-eyes and star-stones
    are one way in which color is displayed in gemstones. 

    Color in gemstones, as it does in all other substances, starts with
    light. Visible light, the light that humans see with the naked eye,
    is only a small part of the total light available. Visible light is
    also called "white light," because it looks white to us. All light
    consists of wavelengths of individual colors. Visible light is a
    combination of color wavelengths that blend to form white. You can
    easily see all the colors in white light when moisture in the air
    separates sunlight into a rainbow after a rain. 

    All solids, including gemstones, separate the colors in light.
    Nearly all substances absorb some color wavelengths. The colors that
    they do not absorb are reflected back. Those reflections are the
    colors that we see. Each gemstone will absorb or reflect different
    color wavelengths depending primarily on the chemicals it contains.
    For example, peridot absorbs all but the green color wavelengths.
    The green is reflected back, making peridot look green to us. Rubies
    absorb everything except red and some blue wavelengths. The red and
    unabsorbed blue are reflected back to us as a deep red color.
    Gemstones appear black when they absorb all color. Some gemstones in
    their chemically pure state don't absorb any color wavelengths.
    Beryl is one example. Because all the colors are reflected back, the
    gemstone is the same color as the light striking it. That makes it
    appear colorless to us. However, tiny amounts of impurities in a
    stone can cause some light to be absorbed rather than reflected.
    Depending on the impurity in beryl, we see green (emerald), blue
    (aquamarine), yellow (heliodor or golden beryl), or pink
    (morganite). 

    While impurities can change the color of the whole gemstone, as with
    the beryls, inclusions change only a part of a stone's appearance.
    Inclusions are relatively large amounts of some foreign substance
    embedded in the gemstone. Because the inclusion has a different
    chemical composition than the gemstone itself, it absorbs and
    reflects different color wavelengths than the gemstone does.
    Although most inclusions are undesirable, some can create effects
    like chatoyancy (cat's-eyes) and asterism (star- stones). 

    Chatoyancy, which comes from the French words for cat and eye, is a
    band of light across a gemstone. It is not on the surface of the
    stone, but comes from within and looks exactly like a cat's eye. The
    inclusions that typically cause chatoyancy are tiny, needle-shaped
    crystals of rutile. Rutile is a colorless mineral that reflects
    light the way diamonds do. To reflect a good cat's-eye, the crystals
    must be lined up parallel to each other. Cat's eyes occur frequently
    in chrysoberyl, but are also found in tourmaline, rubies, sapphires,
    garnets, spinel, and quartz. 

    If the inclusions are lined up in bands in more than one direction,
    with the bands all crossing one another at a middle point, the
    reflected light forms a star. Stars usually have either four or six
    rays. Stars, or asterism, are found primarily in rubies and
    sapphires. Quartz and garnet may also sometimes have stars. Random
    patterns of crystal inclusions may reflect spangles or points of
    light. 

    Tiger's-eye starts as the mineral crocidolite, which contains long,
    asbestos-like fibers. Over time, nature replaces the fibers with
    quartz crystals and the color gradually changes from blue to yellow
    and brown stripes. Tiger's-eye gets its name from the chatoyancy
    visible when it is properly cut. 

    Color is what makes many gemstones valuable, and light is the source
    of that color. Chatoyancy (cat's-eyes) and asterism (star-stones)
    are special reflections of light that add to the beauty and pleasure
    of the gemstones we prize 



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


____________________________________________________________________
T h e   O r c h i d   L i s t
Open Electronic Forum for Jewelry Manufacturing Methods and Procedures
____________________________________________________________________
Orchid FAQ:
~ http://www.ganoksin.com/orchid/faq.htm
Orchid Archives:
~ http://www.ganoksin.com/orchid/archive
Orchid Galleries:
~ http://www.ganoksin.com/orchid/gallery.htm
Invite a Friend:
~ http://www.ganoksin.com/invite.htm
____________________________________________________________________
Tips From The Jeweler's Bench - Article Archive
~ http://www.ganoksin.com/borisat/tip_sear.htm
The Jeweler's Selected Bibliography List
~ http://www.ganoksin.com/jewelry-books
Buy Orchid Jewelry:
~ http://www.ganoksin.com/shop
____________________________________________________________________
-Unsubscribe:
-Email: orchid-request AT ganoksin.com Body=unsubscribe subject=blank
____________________________________________________________________