By R A Higgins
Metheun and Co Ltd
1961
Metheun and Co writes:
The subject of this book is jewellery from Classical lands from the Early Bronze Age (about 2500 B.C) to the Late Roman period (about A.D 400). It thus covers some 3000 years of almost continuous development.
A full account of the technical methods of making jewellery is followed by a description, period by period, of the jewellery itself. Some periods, such as the Etruscan, have been the subject of detailed studies, but others, such as the Minoan and Mycenaean, have been almost completely neglected by students of ancient jewellery. The author, who is an Assistant Keeper at the British Museum, is particularly fortunate to have at his disposal what is perhaps the finest general collection of ancient jewellery in the world. He has experience of excavation, and has worked on material at Mycenae and Knossos.
The narrative is supplemented by very full site-lists and bibliographical references, which serve as a foundation for the arguments brought forward in the text, and as a guide to further reading. There are 68 plates, four in color, and a number of line drawings.
It is hoped that this book will serve not only as an introduction to a fascinating subject, but also as a work of reference for museums, dealers, archaeologists and collectors.
Tuesday, March 27, 2007
Monday, March 26, 2007
Tourmaline - Spinel Doublets
(via ICA Early Warning Flash, No. 36, April 2, 1990) GII writes:
Subject: Beads of Tourmaline-Spinel Doublets in a string of natural rubies.
Observations: The string consisted of 52 beads of red color. Each bead (average weight 20 carats) was individually tested for its gemological properties. 50 pieces were identified as Natural Rubies having inclusions of rutile and some crystal inclusions. All beads were transparent red colored and irregular in shape. All beads were showing dichroism in some position or the other.
Microscopic examination of the beads revealed that two of the beads were actually doublets. One portion of these two beads had typical inclusions of spinel (octahedral crystals and thin liquid films) and the other portion showed characteristic inclusions of tourmaline (thread-like cavities and trachites). On further examination the line of demarcation could also be noticed. Refractive indices (spot method) clearly showed that the beads were doublets of red tourmaline and red spinel; R.I 1.62 and 1.719 for tourmaline and spinel respectively.
Warning: The red colored doublets are beads of irregular shape and can be easily mistaken for rubies in the necklace. It is not sufficient to test only a few pieces in the necklace. The refractive indices for the beads should be obtained from different directions. It is also imperative to check the inclusions for all the beads in a necklace.
Subject: Beads of Tourmaline-Spinel Doublets in a string of natural rubies.
Observations: The string consisted of 52 beads of red color. Each bead (average weight 20 carats) was individually tested for its gemological properties. 50 pieces were identified as Natural Rubies having inclusions of rutile and some crystal inclusions. All beads were transparent red colored and irregular in shape. All beads were showing dichroism in some position or the other.
Microscopic examination of the beads revealed that two of the beads were actually doublets. One portion of these two beads had typical inclusions of spinel (octahedral crystals and thin liquid films) and the other portion showed characteristic inclusions of tourmaline (thread-like cavities and trachites). On further examination the line of demarcation could also be noticed. Refractive indices (spot method) clearly showed that the beads were doublets of red tourmaline and red spinel; R.I 1.62 and 1.719 for tourmaline and spinel respectively.
Warning: The red colored doublets are beads of irregular shape and can be easily mistaken for rubies in the necklace. It is not sufficient to test only a few pieces in the necklace. The refractive indices for the beads should be obtained from different directions. It is also imperative to check the inclusions for all the beads in a necklace.
The Bridges Of Madison County
Memorable quote (s) from the movie:
Francesca (Meryl Streep): Robert, please. You don't understand; no-one does. When a woman makes the choice to marry, to have children; in one way her life begins but in another way it stops. You build a life of details. You become a mother, a wife and you stop and stay steady so that your children can move. And when they leave they take your life of details with them. And then you're expected move again only you don't remember what moves you because no-one has asked in so long. Not even yourself. You never in your life think that love like this can happen to you.
Robert Kincaid (Clint Eastwood): But now that you have it...
Francesca (Meryl Streep): I want to keep it forever. I want to love you the way I do now the rest of my life. Don't you understand... we'll lose it if we leave; I can't make an entire life disappear to start a new one. All I can do is try to hold onto to both. Help me. Help me not lose loving you.
Francesca (Meryl Streep): Robert, please. You don't understand; no-one does. When a woman makes the choice to marry, to have children; in one way her life begins but in another way it stops. You build a life of details. You become a mother, a wife and you stop and stay steady so that your children can move. And when they leave they take your life of details with them. And then you're expected move again only you don't remember what moves you because no-one has asked in so long. Not even yourself. You never in your life think that love like this can happen to you.
Robert Kincaid (Clint Eastwood): But now that you have it...
Francesca (Meryl Streep): I want to keep it forever. I want to love you the way I do now the rest of my life. Don't you understand... we'll lose it if we leave; I can't make an entire life disappear to start a new one. All I can do is try to hold onto to both. Help me. Help me not lose loving you.
How Crystals Grow
(via Wahroongai News, Volume 32, Number 8, August 1998) I Sunagawa writes:
Mechanisms of growth
Single crystal synthetics, for jewelry purposes, are grown by two mechanisms: either growth from the melt, or growth from solution. Natural crystal growth is essentially solution growth—either from high temperature inorganic solutions (magmatic crystallization), or from aequeous solutions (supergene, hydrothermal, pneumatolytic, and metamorphic crystallization).
Melt growth
Single crystal growth from the pure melt phase—using Verneuil, float zone, or skull melt, etc technologies—is quite different from the mechanism of crystal growth that occurs in nature. For example, the curved growth (color zoning) of Verneuil synthetics is due to the fact that the solid-liquid interface in melt growth is atomistically rough (thus providing many sites for attachment of the melt to the interface of the growing crystal), and is curved in concordance with the isotherm at this growth interface. In addition, the spacial distribution of dislocations in melt grown crystals also differs from that of natural crystals—which grow from a solution phase.
Solution growth
Under solution growth conditions growth temperatures are lower, and mass transfer processes and solute-solvent interactions play a large part in the crystallization process. As a consequence, the solid-liquid interfaces of solution grown single crystals are atomistically smoother than those of melt growth crystals. This causes crystals grown from solution to have a tendency to develop polyganol crystal shapes that are bounded by flat low index faces. Indeed, this mechanism of growth is reflected in the habits, faces, surface microtopographies (growth spirals, etc), inhomogeneties, and imperfections in the crystals—and their resulting cut stones. Although natural and synthetic crystals each are grown from solutions phases; the crystals have distinct and identifiable growth features that positively identify their mode of formation. Also, synthetic gemstones grown from solutions phases—such as high temperature flux growth, hydrothermal and aequeous growth—do display a range of growth features that are quite different from those of melt growth synthetics.
In solution growth, the solute-solvent complex is transported from the bulk solution to the solid-liquid (growth) interface by diffusion and/or convection. Here the solute is released from its solvent through a desolvation process. The major driving force for crystal growth is a high concentration diffusion boundary layer that develops at the growth interface of the crystal. The rate at which the solute is incorporated into the crystal structure is controlled by the roughness of this solid-liquid interface.
For example, when the interface is atomistically rough, the universal presence of kink sites allows ready incorporation of the solute by adhesive growth, and so allow the interface to grow homogeneously and at a growth rate normal to the interface that is linearly related to the driving force. In contrast, when the interface is atomistically smooth (consisting of flat terraces, steps, and kinks in the step) the solute has difficulty finding suitable sites (e.g kink in a step, outcrops of screw dislocations) that will allow it to be incorporated into the growing crystal. As a result, growth will proceed through lateral, two dimensional spreading of growth layers parallel to the interface. Growth on smooth interfaces is slowest, so the face will develop as the most developed crystal face.
Summary
1. Crystal growth (and dissolution) rates are anisotropic and are controlled by the degree of roughness of the growth interface, e.g. rough interfaces grow fastest, while smooth interfaces grow slowly but are well developed.
2. Growth rates (habits) are modified by growth parameters such as solvent chemistry, impurity content, growth temperature and pressure, supersaturation, etc.
3. Growth sectors form in single crystals due to anisotropic growth rates associated with impurity partitioning at growth interfaces.
4. Growth rates may fluctuate within growth sectors due to fluctuations in overall growth parameters, or imbalance between diffusion and incorporation rates. This leads to variations in the concentration and distribution of point defects and impurity elements responsible for growth or color banding in growth sectors. Growth banding may be straight and parallel, or curved and hummocky—depending on the roughness of the growth surface interface. For example, natural diamonds {111} growth is straight and parallel, while its {100} growth is hummocky.
5. The partition of elements in the growth solution depends both on thermodynamics and growth kinetics. For example, Nitrogen is more concentrated in {111} sectors in diamond than {100} sectors.
6. Changed conditions during growth often lead to dissolution and regrowth, or transformation from one growth morphology to another.
7. Inclusions are trapped particularly when growth parameters are changed, on the surface of seeds, at growth sector boundaries, and at twin compositional planes. Growth controlling dislocations are often generated by these inclusions.
8. Following crystal growth, exsolution or plastic deformation induced phase changes will superimpose exsolution lamellae, mechanical twin lamellae, and dislocation tangles on pre-existing growth features.
Mechanisms of growth
Single crystal synthetics, for jewelry purposes, are grown by two mechanisms: either growth from the melt, or growth from solution. Natural crystal growth is essentially solution growth—either from high temperature inorganic solutions (magmatic crystallization), or from aequeous solutions (supergene, hydrothermal, pneumatolytic, and metamorphic crystallization).
Melt growth
Single crystal growth from the pure melt phase—using Verneuil, float zone, or skull melt, etc technologies—is quite different from the mechanism of crystal growth that occurs in nature. For example, the curved growth (color zoning) of Verneuil synthetics is due to the fact that the solid-liquid interface in melt growth is atomistically rough (thus providing many sites for attachment of the melt to the interface of the growing crystal), and is curved in concordance with the isotherm at this growth interface. In addition, the spacial distribution of dislocations in melt grown crystals also differs from that of natural crystals—which grow from a solution phase.
Solution growth
Under solution growth conditions growth temperatures are lower, and mass transfer processes and solute-solvent interactions play a large part in the crystallization process. As a consequence, the solid-liquid interfaces of solution grown single crystals are atomistically smoother than those of melt growth crystals. This causes crystals grown from solution to have a tendency to develop polyganol crystal shapes that are bounded by flat low index faces. Indeed, this mechanism of growth is reflected in the habits, faces, surface microtopographies (growth spirals, etc), inhomogeneties, and imperfections in the crystals—and their resulting cut stones. Although natural and synthetic crystals each are grown from solutions phases; the crystals have distinct and identifiable growth features that positively identify their mode of formation. Also, synthetic gemstones grown from solutions phases—such as high temperature flux growth, hydrothermal and aequeous growth—do display a range of growth features that are quite different from those of melt growth synthetics.
In solution growth, the solute-solvent complex is transported from the bulk solution to the solid-liquid (growth) interface by diffusion and/or convection. Here the solute is released from its solvent through a desolvation process. The major driving force for crystal growth is a high concentration diffusion boundary layer that develops at the growth interface of the crystal. The rate at which the solute is incorporated into the crystal structure is controlled by the roughness of this solid-liquid interface.
For example, when the interface is atomistically rough, the universal presence of kink sites allows ready incorporation of the solute by adhesive growth, and so allow the interface to grow homogeneously and at a growth rate normal to the interface that is linearly related to the driving force. In contrast, when the interface is atomistically smooth (consisting of flat terraces, steps, and kinks in the step) the solute has difficulty finding suitable sites (e.g kink in a step, outcrops of screw dislocations) that will allow it to be incorporated into the growing crystal. As a result, growth will proceed through lateral, two dimensional spreading of growth layers parallel to the interface. Growth on smooth interfaces is slowest, so the face will develop as the most developed crystal face.
Summary
1. Crystal growth (and dissolution) rates are anisotropic and are controlled by the degree of roughness of the growth interface, e.g. rough interfaces grow fastest, while smooth interfaces grow slowly but are well developed.
2. Growth rates (habits) are modified by growth parameters such as solvent chemistry, impurity content, growth temperature and pressure, supersaturation, etc.
3. Growth sectors form in single crystals due to anisotropic growth rates associated with impurity partitioning at growth interfaces.
4. Growth rates may fluctuate within growth sectors due to fluctuations in overall growth parameters, or imbalance between diffusion and incorporation rates. This leads to variations in the concentration and distribution of point defects and impurity elements responsible for growth or color banding in growth sectors. Growth banding may be straight and parallel, or curved and hummocky—depending on the roughness of the growth surface interface. For example, natural diamonds {111} growth is straight and parallel, while its {100} growth is hummocky.
5. The partition of elements in the growth solution depends both on thermodynamics and growth kinetics. For example, Nitrogen is more concentrated in {111} sectors in diamond than {100} sectors.
6. Changed conditions during growth often lead to dissolution and regrowth, or transformation from one growth morphology to another.
7. Inclusions are trapped particularly when growth parameters are changed, on the surface of seeds, at growth sector boundaries, and at twin compositional planes. Growth controlling dislocations are often generated by these inclusions.
8. Following crystal growth, exsolution or plastic deformation induced phase changes will superimpose exsolution lamellae, mechanical twin lamellae, and dislocation tangles on pre-existing growth features.
Chameleon Diamonds
(via Wahroongai News, Volume 32, Number 4, April 1998)
Chameleon diamonds are rare hydrogen-rich diamonds that change color when exposed to heat. The most famous named chameleon diamond is the 22.28 ct heat-shaped Green Chameleon diamond—a diamond that changes color from grayish green to bright yellow under one of two circumstances.
Heat the green (stable color) chameleon diamond in the flame of an alcohol lamp to a temperature of 200 – 300ºC and its color will convert to an unstable bright yellow. Overheating to ~ 500ºC. If the unstable yellow colored chameleon diamond is in the dark for 24 of more hours, within a few minutes of its removal form the warm darkness its color will revert from unstable bright yellow to stable green color which is caused by the absorption of UV wavelengths from visible light.
The cause of this chameleon effect is an extremely broad absorption extending from ~ 550nm into the infrared, leaving a green window in the visible. Green chameleon diamonds also display characteristic greenish yellow phosphorescence to LWUV, which may last for several minutes after irradiation ceases.
Over recent years at least two other chameleon-type diamonds have been discovered:
-The first group is some pink Argyle diamonds that briefly change to brownish pink when subjected to strong UV irradiation
-The second group is a single specimen that changes from faint pink to colorless after UV irradiation. Gentle heating returns the faint pink color to this diamond. When exposed to UV light this chameleon has a strong apricot pink fluorescence, but a protracted yellowish green phosphorescence to follow.
Chameleon diamonds are rare hydrogen-rich diamonds that change color when exposed to heat. The most famous named chameleon diamond is the 22.28 ct heat-shaped Green Chameleon diamond—a diamond that changes color from grayish green to bright yellow under one of two circumstances.
Heat the green (stable color) chameleon diamond in the flame of an alcohol lamp to a temperature of 200 – 300ºC and its color will convert to an unstable bright yellow. Overheating to ~ 500ºC. If the unstable yellow colored chameleon diamond is in the dark for 24 of more hours, within a few minutes of its removal form the warm darkness its color will revert from unstable bright yellow to stable green color which is caused by the absorption of UV wavelengths from visible light.
The cause of this chameleon effect is an extremely broad absorption extending from ~ 550nm into the infrared, leaving a green window in the visible. Green chameleon diamonds also display characteristic greenish yellow phosphorescence to LWUV, which may last for several minutes after irradiation ceases.
Over recent years at least two other chameleon-type diamonds have been discovered:
-The first group is some pink Argyle diamonds that briefly change to brownish pink when subjected to strong UV irradiation
-The second group is a single specimen that changes from faint pink to colorless after UV irradiation. Gentle heating returns the faint pink color to this diamond. When exposed to UV light this chameleon has a strong apricot pink fluorescence, but a protracted yellowish green phosphorescence to follow.
Riches Of The Earth
By Frank J Anderson
The Rutledge Press
1981 ISBN 0-8317-7739-7
The Rutledge Press writes:
Because of their beauty and usefulness, ornamental, precious, and semi-precious stones have always had a close relationship with human civilization, whether endowed with religious significance, used as building materials, or wrought into works of art.
Riches of the Earth presents a vivid survey of the unique histories of the major precious and semi-precious stones. Beginning with prehistoric man’s first tools and ending with laser beams and holographs, the chapters of Riches of the Earth deal with religion, magic, superstition; associations with famous people and places; legends, discoveries, forgeries, and thefts. Among the wealth of material are the colorful myths surrounding Chinese jade, the story of ornamental stones during the Middle Ages, the magnificence of the world’s most precious royal collections, the symbolism of stones, stories of beautiful treasures lost, and the real powers of stones used today—plus a chapter on the what, where, and how of collecting.
Forty eight pages of full color illustrations enhance this fascinating history of man’s ongoing enchantment with stones. Riches of the Earth is a delight for the connoisseur and a display of excellence to inspire every collector of rocks and minerals.
The Rutledge Press
1981 ISBN 0-8317-7739-7
The Rutledge Press writes:
Because of their beauty and usefulness, ornamental, precious, and semi-precious stones have always had a close relationship with human civilization, whether endowed with religious significance, used as building materials, or wrought into works of art.
Riches of the Earth presents a vivid survey of the unique histories of the major precious and semi-precious stones. Beginning with prehistoric man’s first tools and ending with laser beams and holographs, the chapters of Riches of the Earth deal with religion, magic, superstition; associations with famous people and places; legends, discoveries, forgeries, and thefts. Among the wealth of material are the colorful myths surrounding Chinese jade, the story of ornamental stones during the Middle Ages, the magnificence of the world’s most precious royal collections, the symbolism of stones, stories of beautiful treasures lost, and the real powers of stones used today—plus a chapter on the what, where, and how of collecting.
Forty eight pages of full color illustrations enhance this fascinating history of man’s ongoing enchantment with stones. Riches of the Earth is a delight for the connoisseur and a display of excellence to inspire every collector of rocks and minerals.
Sunday, March 25, 2007
My Fair Lady
Memorable quote (s) from the movie:
Mrs. Higgins (Gladys Cooper): However did you learn good manners with my son around?
Eliza Doolittle (Audrey Hepburn): It was very difficult. I should never have known how ladies and gentlemen really behaved, if it hadn't been for Colonel Pickering. He always showed what he thought and felt about me as if I were something better than a common flower girl. You see, Mrs. Higgins, apart from the things one can pick up, the difference between a lady and a flower girl is not how she behaves, but how she is treated. I shall always be a common flower girl to Professor Higgins, because he always treats me like a common flower girl, and always will. But I know that I shall always be a lady to Colonel Pickering, because he always treats me like a lady, and always will.
Mrs. Higgins (Gladys Cooper): However did you learn good manners with my son around?
Eliza Doolittle (Audrey Hepburn): It was very difficult. I should never have known how ladies and gentlemen really behaved, if it hadn't been for Colonel Pickering. He always showed what he thought and felt about me as if I were something better than a common flower girl. You see, Mrs. Higgins, apart from the things one can pick up, the difference between a lady and a flower girl is not how she behaves, but how she is treated. I shall always be a common flower girl to Professor Higgins, because he always treats me like a common flower girl, and always will. But I know that I shall always be a lady to Colonel Pickering, because he always treats me like a lady, and always will.
A Couple Of Unusual Diamonds
(via Wahroongai News, Volume 32, Number 4, April 1998)
The appearance in the marketplace of parcels of saturated greenish yellow to yellowish green to brownish fancy colored diamonds—with unusual characteristics—has led to suggestions that these colors could have been induced by a new hyperbaric heating treatment that consists of high temperature and pressure heat treatment (? in a Russian Bars apparatus) that reverses naturally occurring aggregation of nitrogen in the diamonds. Suggested source material for this treatment is low quality, mostly Argyle-type natural diamonds.
The treated diamond’s color has two components: a saturated yellow to brownish body color and a strong greenish luminescence to strong visible light emitted by distinctively visible brownish yellow growth lines in the diamond. This gives the green transmitter diamond’s body color a greenish overcast that is readily visible in daylight. When viewed in somewhat subdued lighting these strongly green fluorescent growth lines often contrast strongly against the brownish body color of the diamonds. When exposed to LWUV the growth lines fluoresce a strong green. Examination of the diamond under magnification reveals prominent graining and color zoning paralleling octahedral faces, pitted and corroded (? burnt) facet junctions, girdle, external surfaces of surface-reaching fractures, and heavily bearded girdles.
Examination with gemological hand-held spectroscope revealed pairs of absorption and bright emission lines at 513 and 518nm, absorption lines at 415 (N3 center) and 503nm (H3 center), and a broad absorption band between 465 and 494nm. A more detailed examination with a spectrophotometer confirmed the presence of these features and added a weak absorption peak at 637nm and a weak to strong peak at 985nm (in the invisible near-infrared)—which was assigned to the irradiation high temperature (>1400ºC) annealing induced H2 center.
It is concerning that none of these obviously treated greenish yellow to yellow green to brown diamonds displayed the 595nm, 741nm (GR1) or HIb and HIc absorptions that would be expected to be found in irradiated and heat treated yellow or green diamonds.
The appearance in the marketplace of parcels of saturated greenish yellow to yellowish green to brownish fancy colored diamonds—with unusual characteristics—has led to suggestions that these colors could have been induced by a new hyperbaric heating treatment that consists of high temperature and pressure heat treatment (? in a Russian Bars apparatus) that reverses naturally occurring aggregation of nitrogen in the diamonds. Suggested source material for this treatment is low quality, mostly Argyle-type natural diamonds.
The treated diamond’s color has two components: a saturated yellow to brownish body color and a strong greenish luminescence to strong visible light emitted by distinctively visible brownish yellow growth lines in the diamond. This gives the green transmitter diamond’s body color a greenish overcast that is readily visible in daylight. When viewed in somewhat subdued lighting these strongly green fluorescent growth lines often contrast strongly against the brownish body color of the diamonds. When exposed to LWUV the growth lines fluoresce a strong green. Examination of the diamond under magnification reveals prominent graining and color zoning paralleling octahedral faces, pitted and corroded (? burnt) facet junctions, girdle, external surfaces of surface-reaching fractures, and heavily bearded girdles.
Examination with gemological hand-held spectroscope revealed pairs of absorption and bright emission lines at 513 and 518nm, absorption lines at 415 (N3 center) and 503nm (H3 center), and a broad absorption band between 465 and 494nm. A more detailed examination with a spectrophotometer confirmed the presence of these features and added a weak absorption peak at 637nm and a weak to strong peak at 985nm (in the invisible near-infrared)—which was assigned to the irradiation high temperature (>1400ºC) annealing induced H2 center.
It is concerning that none of these obviously treated greenish yellow to yellow green to brown diamonds displayed the 595nm, 741nm (GR1) or HIb and HIc absorptions that would be expected to be found in irradiated and heat treated yellow or green diamonds.
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