A garnet and glass doublet, also known as garnet-topped doublet (GTD) consists of a thin cap of almandine garnet fused to a piece of colored glass imitating a gem. The doublet was popular in the 18th and 19th century, and may still turn up in antique jewelry today.
The reason for constructing this type of doublet is to increase the surface luster on the table of a gemstone. For those who are unaware may think the stone is valuable, but it is easily detectable by the following means.
- The first step is to clean and examine the stone. Visual observation provides you with the chance to examine and classify all aspects of the physical appearance of the gem.
- Check the refractive index. Refractive index of the table will be that of almandine (1.76 or above).
- Refractive index of any pavilion facet will be within the glass range (1.50 - 1.70).
- Use the microscope. The luster difference between garnet top and the glass will become obvious.
- Do the red-ring test by placing the garnet-topped doublet face down on a white background. You will see a faint red ring inside the girdle outline representing the boundary of the garnet cap.
- Immersion technique. When you immerse the stone in a suitable liquid, you are able to see any color difference between the two materials.
- Fluorescence. This is a complimentary test. View the gem parallel to the girdle plane under long wave and short wave ultraviolet light. Garnet will show inert reaction, while glass may show chalky fluorescence.
Friday, February 09, 2007
Gems And Gem Art
Programa Royal Collections Group writes:
Gazing at the world’s biggest topaz, enjoying the rare sight of a gem embedded in a meteorite or marvelling at centuries-old sculptures made from precious stones are all culturally enriching experiences for people from all walks of life.
But the aim of PRC (Programa Royal Collection) is not only to exhibit unique collections but also to convert these experiences into a discovering and learning process that goes well beyond mere passive observation. This twofold experience of enjoying and learning in tandem is the keynote idea of our exhibition philosophy.
In the case of the gem exhibitions, for example, the precious stones are accompanied with educational display cases containing such exhibits as gemmological maps, uncut gems, laboratory material, polishing and cutting equipment, etc., all designed to raise public awareness of gems and gem art. These display cases are backed up by a wealth of informative material in different languages and with different levels of specialisation: posters for display cases, information panels, photographs, fact files, brochures, catalogues, etc. Visitors are thus enabled to discover numerous aspects of the world of gems, such as their formation, mining, physical characteristics (hardness, optical effects, cleavage...), cutting, authentication, what makes a synthetic gem different from a false gem and many other fascinating facts and snippets.
More info @ http://www.royalcollections.es/ingles/queofreceprc/interesdidactico/interesdidactico.htm
Gazing at the world’s biggest topaz, enjoying the rare sight of a gem embedded in a meteorite or marvelling at centuries-old sculptures made from precious stones are all culturally enriching experiences for people from all walks of life.
But the aim of PRC (Programa Royal Collection) is not only to exhibit unique collections but also to convert these experiences into a discovering and learning process that goes well beyond mere passive observation. This twofold experience of enjoying and learning in tandem is the keynote idea of our exhibition philosophy.
In the case of the gem exhibitions, for example, the precious stones are accompanied with educational display cases containing such exhibits as gemmological maps, uncut gems, laboratory material, polishing and cutting equipment, etc., all designed to raise public awareness of gems and gem art. These display cases are backed up by a wealth of informative material in different languages and with different levels of specialisation: posters for display cases, information panels, photographs, fact files, brochures, catalogues, etc. Visitors are thus enabled to discover numerous aspects of the world of gems, such as their formation, mining, physical characteristics (hardness, optical effects, cleavage...), cutting, authentication, what makes a synthetic gem different from a false gem and many other fascinating facts and snippets.
More info @ http://www.royalcollections.es/ingles/queofreceprc/interesdidactico/interesdidactico.htm
All About Eve
A memorable quote from the movie:
Margo Channing (Bette Davis): Funny business, a woman's career, the things you drop on the way up the ladder so you can move faster. You forget you'll need them again when you get back to being a woman. It's one career all females have in common - being a woman. Sooner or later we've got to work at it no matter how many other careers we've had or wanted. And in the last analysis nothing is any good unless you can look up just before dinner or turn around in bed and there he is. Without that you're not a woman. You're something with a French provincial office or a book full of clippings but you're not a woman. Slow curtain, the end.
Margo Channing (Bette Davis): Funny business, a woman's career, the things you drop on the way up the ladder so you can move faster. You forget you'll need them again when you get back to being a woman. It's one career all females have in common - being a woman. Sooner or later we've got to work at it no matter how many other careers we've had or wanted. And in the last analysis nothing is any good unless you can look up just before dinner or turn around in bed and there he is. Without that you're not a woman. You're something with a French provincial office or a book full of clippings but you're not a woman. Slow curtain, the end.
The Federal Trade Commission’s Guide for the Jewelry, Precious Metals and Pewter Industries
FTC writes:
23.15 Misuse of the term "properly cut," etc.
It is unfair or deceptive to use the terms "properly cut," "proper cut," "modern cut," or any representation of similar meaning to describe any diamond that is lopsided, or is so thick or so thin in depth as to detract materially from the brilliance of the stone.
Note to 23.15: Stones that are commonly called "fisheye" or "old mine" should not be described as "properly cut," "modern cut," etc.
More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm
23.15 Misuse of the term "properly cut," etc.
It is unfair or deceptive to use the terms "properly cut," "proper cut," "modern cut," or any representation of similar meaning to describe any diamond that is lopsided, or is so thick or so thin in depth as to detract materially from the brilliance of the stone.
Note to 23.15: Stones that are commonly called "fisheye" or "old mine" should not be described as "properly cut," "modern cut," etc.
More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm
Methuen Handbook of Color
By A Korenerup & J H Wanscher
Politikens Forlag, Copenhagen
Methuen London
1961 / 1989 ISBN 0-413-33400-7
Methuen writes:
The third edition of this authoritative pocket color book covers the essentials of color practice and includes an international dictionary of colors with British standard equivalents. A universal ready reference for all those whose jobs or recreation involves color, it now includes names of colors used by British paint manufacturers and colors traditionally associated with the printing ink industry, thus shedding light on the whole field of color in art and science.
The color book is divided into two parts, the Handbook proper and a Color Dictionary. The Handbook explains the basic facts upon which all systems of color identification are based, and describes some important visual effects that apply to color usage generally. The Dictionary consists of plates of 1266 color samples accompanied by descriptive glossaries of color names with an easy cross reference system.
The Color Dictionary is so contrived that a color sample of one’s own can be compared with the charted samples, and an appropriate name selected for it from the color diagrams. On the other hand, the appearance of a named color can be discovered by looking up the color name in alphabetical list and following the reference symbol to the appropriate place on the color plates.
Lists of color names used by British paint manufacturers and those used by the printing ink industry are included, set out in such a way that they can be readily compared with the colors reproduced in the Dictionary.
Politikens Forlag, Copenhagen
Methuen London
1961 / 1989 ISBN 0-413-33400-7
Methuen writes:
The third edition of this authoritative pocket color book covers the essentials of color practice and includes an international dictionary of colors with British standard equivalents. A universal ready reference for all those whose jobs or recreation involves color, it now includes names of colors used by British paint manufacturers and colors traditionally associated with the printing ink industry, thus shedding light on the whole field of color in art and science.
The color book is divided into two parts, the Handbook proper and a Color Dictionary. The Handbook explains the basic facts upon which all systems of color identification are based, and describes some important visual effects that apply to color usage generally. The Dictionary consists of plates of 1266 color samples accompanied by descriptive glossaries of color names with an easy cross reference system.
The Color Dictionary is so contrived that a color sample of one’s own can be compared with the charted samples, and an appropriate name selected for it from the color diagrams. On the other hand, the appearance of a named color can be discovered by looking up the color name in alphabetical list and following the reference symbol to the appropriate place on the color plates.
Lists of color names used by British paint manufacturers and those used by the printing ink industry are included, set out in such a way that they can be readily compared with the colors reproduced in the Dictionary.
Thursday, February 08, 2007
Corundum Doublets
The most likely place to find doublets and triplets is in antique jewelry. It is also possible to find doublets and triplets in new pieces.
Assembled stones normally consist of two parts (doublets) or three parts (triplets) glued together for the following reasons:
- to provide a better wearing surface.
- to obtain a large stone from two smaller pieces of natural gem material.
- to provide better color and appearance.
The purpose of producing corundum doublet is to have the careless buyer look into the table of the stone, see the natural inclusions on the crown area, then purchase the gem at a high price. This deception is possible because of the thin crown of colorless or light yellowish green sapphire does not influence the color the stone face up (table-up), which is determined by the synthetic material on the pavilion. Few buyers actually check the girdle of the stone. Corundum doublets are easy to detect if the buyer is aware of their features. The careless buyer can easily be fooled.
When you are trying to identify an unknown stone always suspect an assembled stone. To avoid the mother-of-all surprise you should look for the difference in color, luster or inclusions, plane of join, gas bubbles (if any) between the crown and pavilion (base) of the gem material. Doublets consisting of black star sapphire on the crown and pavilion of lower quality natural sapphire is also common. There is also doublet made of a base of a black, non-transparent layer of natural star sapphire topped with synthetic orange sapphire or synthetic spinel (flame fusion). Use good lighting and proper magnification to view the color contrast so that you are able to identify the stone.
Assembled stones normally consist of two parts (doublets) or three parts (triplets) glued together for the following reasons:
- to provide a better wearing surface.
- to obtain a large stone from two smaller pieces of natural gem material.
- to provide better color and appearance.
The purpose of producing corundum doublet is to have the careless buyer look into the table of the stone, see the natural inclusions on the crown area, then purchase the gem at a high price. This deception is possible because of the thin crown of colorless or light yellowish green sapphire does not influence the color the stone face up (table-up), which is determined by the synthetic material on the pavilion. Few buyers actually check the girdle of the stone. Corundum doublets are easy to detect if the buyer is aware of their features. The careless buyer can easily be fooled.
When you are trying to identify an unknown stone always suspect an assembled stone. To avoid the mother-of-all surprise you should look for the difference in color, luster or inclusions, plane of join, gas bubbles (if any) between the crown and pavilion (base) of the gem material. Doublets consisting of black star sapphire on the crown and pavilion of lower quality natural sapphire is also common. There is also doublet made of a base of a black, non-transparent layer of natural star sapphire topped with synthetic orange sapphire or synthetic spinel (flame fusion). Use good lighting and proper magnification to view the color contrast so that you are able to identify the stone.
Forrest Gump Movie
A memorable quote from the movie:
Forrest Gump (Tom Hanks): My momma always said, "Life was like a box of chocolates. You never know what you're gonna get."
Forrest Gump (Tom Hanks): My momma always said, "Life was like a box of chocolates. You never know what you're gonna get."
The Federal Trade Commission’s Guide for the Jewelry, Precious Metals and Pewter Industries
FTC writes:
23.14 Misuse of the term "blue white."
It is unfair or deceptive to use the term "blue white" or any representation of similar meaning to describe any diamond that under normal, north daylight or its equivalent shows any color or any trace of any color other than blue or bluish.
More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm
23.14 Misuse of the term "blue white."
It is unfair or deceptive to use the term "blue white" or any representation of similar meaning to describe any diamond that under normal, north daylight or its equivalent shows any color or any trace of any color other than blue or bluish.
More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm
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