Natural And HPHT-annealed Pink And Blue Diamonds

(via Gemmology Queensland, Vol 3, No.1, Jan 2002/IGC Conference Madrid 2001) George Bosshart writes:

The Gubelin Gem Lab engaged in a new study of HPHT-annealed specimens in order to elaborate criteria for the separation of the fancy diamond colors produced by the General Electric Company from the natural pink and blue colors. The key characteristics of the natural colors are briefly outlined and first indicators for HPHT treatment detection are given below.

Natural pink colors exist in both type Ia and type IIa diamond but exhibit a wider color variety in the first group. Type Ia diamond is found in pure pink to red to purple hues but pink and red are more frequently combined with orange and brown color modifiers. Type IIa diamond is limited to light pink to pink hues which may be modified by secondary orange or brown colors. Red hues do not occur in this group but purple does, as a rare and subordinate modifier at least.

In our natural pink study group of over 100 gem quality diamonds, 75% belonged to type Ia, 2% to the mixed type IbIaA, and 22% to type IIa (of which 15% revealed nitrogen-free infrared survey spectra, whereas 7% showed trace amounts of nitrogen as A or B aggregates or as single nitrogen).

In pink type Ia diamond in particular, an irregular color lamination and patchiness can frequently be observed under magnification. These obvious disturbances are plausibly interpreted as being caused by internal plastic deformation which itself is a reaction of the diamond structure to the impact of geotectonic shear stress (active during orogenetic phases), thus avoiding breakage. However, the cause for the pink color center, a wideband absorption centered at 560nm (2.2 eV), is not known in detail.

The strength of the 560nm absorption band determines the intensity of the type Ia pink color. Pink changes to red or purple when this band reaches higher amplitudes (with absorption coefficients in the order of 0.6 cm¯¹ and above). Nitrogen contents in the form of A and/or B aggregates vary in natural pink diamond from extremely small (in type IIa) to extremely large. In type Ia diamond, hydrogen may be present as well, however, in minor to moderate amounts only. Type IIa diamond features the same 560 nm absorption system and an identical but limited intensity relationship (mentioned above). It follows that neither nitrogen nor hydrogen impurities cause the pink color.

In pink diamond, a slight increase of the general absorption in the blue to violet regions of the spectrum results in an orange color modifier which in turn may alter to a brown modifier when the underlying absorption rises more strongly. This absorption is caused by another, equally unknown type of structural defect in the diamond crystal lattice.

In addition to the above color centers, N3 and H3 absorption in type Ia diamond may add a yellowish to orangy modifier component when present in some strength. This combination is typically encountered in Argyle and Brazilian brownish to purplish pink and red diamond. A rarely occurring 480nm absorption band adds a pure orange component to pink diamond colors.

Natural blue diamond varies less than in hue than pink color group. The only modifier of importance is gray. Natural blue occurs in type IIb diamond exclusively (rare specimens being gray violet rather than blue and belonging to hydrogen-rich type IaB). Type IIb diamond is an electric semiconductor due to the substitution of carbon atoms by ppb amounts of boron on the lattice sites of diamond.

The absorption diagram of blue diamond is characterized by a unique mid-infrared absorption superimposed n the inherent diamond absorption in the two-phonon region, with lesser absorption in the adjacent one and three phonon areas. The strongest absorption band is situated at 2802 wavenumbers. It is also typical for blue diamond that the absorption level steadily decreases from the mid-infrared through the near-infrared and visible regions into the ultraviolet part of the electromagnetic spectrum without showing any absorption bands. The absorption minima of blue diamonds fluctuate from 240nm at the base of the fundamental absorption edge to about 500nm. This variation does have an influence on the exact hue of the blue colors which may range from violetish to slightly greenish blue. The dominant wavelengths, as determined by colorimetric measurement, lie in the 465 to 495nm region and confirm that the primary hue is blue. Only one specimen was encountered so far with a dominant wavelength of 435nm corresponding to a violet-blue hue.

The hues of type IIb diamonds frequently are not easy to determine visually due to their weak color saturations and relatively high tones. The type IIb infrared absorption, e.g. the 2802 wn band, could serve as an indicator for the saturation of blue since it is related to the boron content. However, the absorption coefficient of this and other MIR absorption bands for some reason does not appear to be straightforward measure of the blue saturation of type IIb diamond. When the general absorption in type IIb diamond rises to higher levels, and this is particularly important in the visible part of the spectrum, the color impression shifts to bluish gray and even to neutral gray colors (44% of the blue group of 75 specimens grade blue, 40% mixed blue to gray, 8% neutral gray and 1% violet blue).

There is a small proportion (7%) of type IIb diamonds which possesses an increased absorption in the entire ultraviolet region. Accordingly their absorption minimum is more pronounced than in the pure blue colors and shifts into the center of the visible region, with dominant wavelengths ranging from about 500 to slightly over 600nm. Such diamonds essentially appear gray with a greenish to yellowish color modifier. It is interesting to note that greenish gray and yellowish gray colors also occur in type Ia diamond, showing high B nitrogen aggregate and high hydrogen contents, respectively high A aggregate and H contents.

The presence of gray color modifier in type IIb blue diamond may be interpreted as a color generated by the combination of boron with single nitrogen or other chemical impurities and/or by structural defects. However, gray color may also be independent of boron traces at all. A very weak 270 nm band was encountered in several natural blue diamonds and is allocated to single nitrogen.

HPHT Pink and Blue
Prior to 1999, it may have appeared inconceivable that natural off-color diamonds could be improved to obtain the best colors known (D to H color grades), i.e. colorlessness. However, the General Electric Company successfully achieved this breakthrough by applying a modified version of the high pressure/high temperature technology used to grow synthetic diamonds. Since the turn of the millennium, GE has been marketing these virtually colorless diamonds predominantly on the American market and under the brand name, Bellataire (formerly GE POL).

Fancy pink and blue diamond colors are described ad desirable as the white ones. As a consequence, the production of pink and blue became the second great challenge and in 2000. GE managed to add convincing pink and blue color replicas to the wide range of already existing treated diamond colors. In contrast to those irradiated and annealed pink to purple and irradiated blue to green diamond colors, General Electric’s latest products look entirely natural. The exact starting material and its abundance will not be made public by GE. However, experience gained in our study of GE POL diamonds before and after HPHT-annealing (Smith et. al 2000) tells us that the potentially improvable diamond rough must be restricted to type IIa brown respectively type IIB gray to brown specimens of fairly high clarity grades. This implies that the number of diamonds HPHT-annealable to pink and blue colors is considerably inferior to that of the colorless type IIa specimens and that most of the enhanced fancy colors may be low in intensity. A preliminary sampling consisted of six (0.14 to 8.55 ct) pink and two (0.21 and 0.27 ct) blue diamonds HPHT-annealed by GE. The pink stones investigated evidenced that only type IIa and near-type IIa diamonds had been selected. Colorimetric data showed that the resulting pink and blue hues are well within the range of their natural type IIa resp. IIb counterparts. Red or strong blue colors were not observed in this batch, but it included light to intense pink to purple pink colors plus one faint blue and one medium blue specimen each. Brown resp. gray modifiers were subordinate. At this moment, it is safe to state that, comparable to colorless Bellataire diamonds, gemological standard methods (microscopy, UV fluorescence etc.) will not permit a safe separation of natural and HPHT-annealed type IIa pink and semi-conductive blue diamonds. The mid-infrared and UV/VIS spectra of five (out of six) pink samples revealed nitrogen (A or B aggregates, N3 and N9 centers), however, in trace amounts only. The spectra of the blue specimens were very similar to those of the natural colors as well.

Among the optical techniques, Raman photo-luminescence with He/Cd and an Arion laser offer the most promising results. The color enhanced diamonds showed a smaller number of PL bands than recorded for natural colors and the intensities of the bands also differed noticeably. As an example, the 575nm and 637nm bands of the Nº and N centers respectively were definitely stronger than in natural pink diamonds. More and improved criteria are to be expected for both color groups from a larger data base. Advanced testing methods such as X-ray topography or cathodoluminescence applied during our former investigation of eleven colorless diamonds before and after HPHT processing by GE were not used for reasons of limited time and absence of diamonds selected to be processed.

What can be expected as the ultimate achievements in color enhancement by HPHT-annealing?
Cape series diamond becoming colorless and brown resp. gray diamond adopting other colors than colorless, pink or blue.

The Five Ages Of A Lecturer

(via Wahroongai News, Volume 31, Number 3, March 1997)

In How Professors Develop as Teachers, Peter Kugel (TLDU Talk, Issue No.3, July 1996—Teaching and Learning Development Unit, University of Waikato quoting Peter Kugel’s (1993) How Professors Develop as teachers, studies in Higher Education) suggests five distinct stages in the development of a teacher in higher education, and the transitions between each of these stages.

Stage 1: Focus on self
At the start of their teaching career, Kugel suggests, lecturers are mainly concerned with themselves, and more specifically with their survival in front of their first few classes.

Transition 1—self to subject. Once they know they can survive, and even start to feel good about their teachings, their focus shifts rapidly to the subject matter.

Stage 2: Focus on subject
Here the lecturer rediscovers their enthusiasm for their subject, and works hard to extend their knowledge further and then to share it all with their students.

Transition 2—subject to student. After a while, the lecturer may start to notice that students are not learning all that the lecturer is teaching, and may not all share the lecturer’s enthusiasm. Why might this be?

Stage 3: Focus on student
The lecturer sees how greatly students differ one another—in approach to learning, in interest, in motivation, in competence. The lecturer starts to adopt a wider variety of approaches to engage the heterogeneous body of students before them. The lecturer’s interest shift from ‘what am I saying?’ to ‘what are they hearing?’

Transition 3—students as receiver to student as active learner. Even when focusing on the students, the lecturer was still concentrating on what she or he was doing to the students rather than on what the students were doing. The lecturer is now finding limits to what this can achieve.

Stage 4: Focus on student learning
The lecturer increasingly devises appropriate student activities and opportunities for learning.

Transition 4—student as active learner to student as independent learner. The more actively the students engage with their work, the more responsibility they take for their own and each other’s learning.

Stage 5: Focus on the student as an independent learner
When the student truly knows how to learn for her or himself, the lecturer’s work with that student is successfully complete.

Body Jewellery

By Donald Willcox
Sir Isaac Pitman and Sons Ltd
1974 ISBN 0-273-00723-8

Sir Isaac Pitman and Sons writes:

Essentially a pictorial survey of the best in international jewellery design today, Body Jewellery is made up of essays by those designers who have contributed pieces of work to the photographic section.

The designers range from the world famous to less well-known but successful beginners. Donald Willcox provides the summarizing introduction. A variety of topics are covered: from technical aspects of jewellery work to general views on the way jewellery design is developing or ought to develop. The writers all share a determination to break away from the confining tradition of gold and silver jewellery for the ears, wrist, neck and fingers, and to incorporate instead more of the artist’s imagination in ornaments for virtually any part of the body, made out of more or less any malleable material.

Jewellery craftsmen will find ideas and encouragement here. With over 400 illustrations, it is a valuable book for art students and a useful reference for designers.

Donald Willcox describes himself as an ‘author, lunatic, poet, craftsmen, critic and educator..’. He is the author of three poetry books and many on design and crafts, including Leather, which is also published by Pitman. His articles have been widely published in such magazines as Craft Horizons and American Artist.

Synthetic Corundum

(via Wahroongai News, Volume 23, Number 2, February 1989)

The natural growth angle (angle to the c-axis on which the atoms of Al2O3 will stack) of the Verneuil corundum boule is 60°.

Boules grown on seeds cut at 90° to the c-axis have square cross sections.

Boules grown on seeds cut at 0° to the c-axis fracture readily…..both during growth, and during cooling or subsequent cutting.

It is not possible to cut or shape any Verneuil corundum boules until they have been adequately annealed to remove stresses induced during their growth.

Impurities of materials, bubbles, included unmelted powder particles, poor dissemination of the chromophore, and an unclean vertical blowtorch—all contribute to the production of poor quality boules.

The Lost Weekend

Memorable quote (s) from the movie:

Don Birnam (Ray Milland): It shrinks my liver, doesn't it, Nat? It pickles my kidneys, yeah. But what it does to the mind? It tosses the sandbags overboard so the balloon can soar. Suddenly I'm above the ordinary. I'm competent. I'm walking a tightrope over Niagara Falls. I'm one of the great ones. I'm Michaelangelo, molding the beard of Moses. I'm Van Gogh painting pure sunlight. I'm Horowitz, playing the Emperor Concerto. I'm John Barrymore before movies got him by the throat. I'm Jesse James and his two brothers, all three of them. I'm W. Shakespeare. And out there it's not Third Avenue any longer, it's the Nile. Nat, it's the Nile and down it moves the barge of Cleopatra.

(New) Russian Tanzanite Imitation

Jewellery News Asia (August, 1999) writes:

A visually effective tanzanite imitation of Russian manufacture has entered the marketplace. This imitation is potentially confusing as it displays greenish blue to purplish pink directional pleochroism. Investigations by Shane McClure of GIA’s Gem Trade Lab in New York have revealed that this imitation is a synthetic forsterite (magnesium silicate)…..the magnesian end member of the forsterite-fayalite solid solution series of which the gemstone peridot is an intermediate member.

According to McClure the presence of scattered ‘pinpoints’ and small ‘needles’ suggest that this man-made material has been synthesized by the crystal pulling (Czochralski) technique. This imitation which is doped by cobalt, and therefore should display Co absorption spectrum and fluoresces red under LWUV and the Chelsea filter; specific gravity is 3.42 and refractive index is 1.635-1.670.

American Freshwater Pearls

(via Wahroongai News, Volume 33, No.8, August 1999)

The freshwater mussels of the rivers and lakes of North America produce a surprising range of both natural and cultural pearls.

Natural pearls
North American Indians, who lived along the rivers and lakes of North America, made use of indigenous freshwater mussels both as a source of food and as a valued source of pearls for ornamental purposes. By the mid 16th century Spanish explorers also had become aware of and greatly appreciated this source of natural pearls.

Following the mid-19th century discovery of pearls in Notch Brook near Paterson, New Jersey, an active trade in these pearls and their shells began in North America. This trade exploded some decades later as pearl shelling also developed along the rivers of Ohio, Wisconsin, Tennessee, and Arkansas. By the end of World War II these fisheries were no longer economically viable, as plastic has supplanted pearl shell for the manufacture of buttons. The pearl shelling industry of North America revived during the early 1950, when Japanese demand for shells for the manufacture of bead nuclei suitable implanting into Akoya oysters became paramount. Today, natural pearls are still recovered from these rivers and lakes; but only as a by-product of the pearl shelling industry.

Many species of bivalve freshwater mollusk, belonging to the family Unionidae, inhabit the sandy-gravely bottoms of fast flowing rivers, and to a lesser extent the more muddy bottoms of gravely lakes of the Mississippi and its tributaries. However, over the last century damming these rivers, increased silting from agriculture and strip mining, and the introduction of competitive predators such the zebra mussel have decimated the native mussel population of North America. Today hardy survivors such as the pigtoe (Pleerobema cordatum) maple leaf (Quadrula quadrula), three ridge (Amblema costata), and washboard (Megiaonaias gigantean) are still surviving with some difficulty.

Natural pearl form as a result of small pieces of mantle tissue dislodged from mussels by the bites of predatory fish, by invasion of the mussel’s body tissues by boring parasites, or by the accidental implantation of fragments of shell or fish scales into mantle tissues. The shape of pearls obtained from these freshwater mussels varies with where they grow within the mussel. For example, round pearls form in or around the posterior adductor muscle, adjacent beak area, or the body of the mollusk. It is hypothesized that the opening and closing of valves of the mussel rotates the forming pearl thus producing an even distribution of nacre. Elongated symmetrical shapes of pearl form between the adductor muscle and the hinge: with ridged barrels probably resulting from the forming pearl rotating against a projection from the hinge. Button shaped pearls and turtle backs (with flattish bottoms) are found near the outer lips of the valves. Flattish teardrop shaped ‘wings’ form in the posterior hinge area, while more angular chunky pearls form in the anterior hinge area. Rare bumpy rosebud pearls either form in the beak area or deep within the body of the mussel. Colors of natural pearls range from common white to attractive pastel shades of pink, rose, lavender and purple. The lusters of these pearls vary widely. Major factors controlling the color and luster of these freshwater pearls include the distribution of color across the shell of various species of mussel, location of the pearl in the mussel, the health of the mussel, and water and environmental conditions under which the pearl grew.

Cultured pearls
In the early 1960s the Tennessee Shell Company—the major supplier of freshwater shell for the manufacture of beads for the Japanese Akoya industry—began experiments in the culture of freshwater pearls in a man-made TVA lake near Lexington, Tennessee. These experiments were initiated by John Latendresse and his Japanese-born wife. Twenty years later and with the assistance of available Japanese freshwater pearl cultivating technology, pearl culture farms had been set up and were operating economically in several unpolluted lakes leased from TVA.

American cultured pearls are produced in the following sequence, based on basic Lake Biwa technology:

- Individual hookah-equipped divers collect mature mother mussels from the Mississippi River and its tributaries; care being taken that younger mussels are left to continue breeding.
- The harvested mussels are placed into pockets of ‘kangaroo’ nets that hold up to 18 shells. Shells are then transported to the pearl farm where, following inspection and sorting, the mussels are suspended vertically from rafts made from sealed polythene pipes that are so arranged as to leave sufficient space between both mussels and nets to allow the bivalves to recuperate (for at least a month) to feed, to grow, and indeed to spawn. ‘Mother shells’ are kept separated from ‘sacrifice’ mussels.
- Nucleation occurs at the farm using American-trained technologists and American implant technology based in traditional Japanese methods. Once cleaned, the ‘mother shells’ are held in troughs located in the implant lab.
- Because of their large size American freshwater mussels are multi-nucleated using MOP beads of various shapes.
- Three types of pearls are produced: hemispherical blister pearls, bead nucleated whole pearls of various shapes, keshis.
- Following recuperation under the controlled conditions of laboratory-based ‘ponds’, the implanted mussels are returned to the pearl farm for periods ranging from 1½ (for blister pears) to 3-5 years (for whole pearls) depending on the nature of the implant.
- For blister pearls the shells are first cleaned, their cultured blister pearls sawn from the shell, and the sawn edges shaped and polished either to free from or calibrated sizes.
- Fancy shape free pearls, cultivated in the body of the mussel, are covered by killing the mussel at harvest. Due to shaped nuclei these pearls are available in a range of interesting shapes that include marquise, teardrop, bar, marquise, disc, triangle etc.,--with and without bumps, circles, and nodelles (fish-tails).
- Factors determining the grade of these pearls include their luster, orient, color, shape and color.
- Over the years mortality rates for American freshwater cultured pearls have been reduced to less than 5%.

Nineteenth Century Jewellery

By Peter Hinks
Faber and Faber Ltd
1975 ISBN 0-571-10650-1

Faber and Faber writes:

More jewellery was made in Europe during the nineteenth century than in any other period before or since. What is more, the jewellery was extremely varied—the predilections, obsessions and changing circumstances of England, France, Italy and Germany, for example, being faithfully reflected in their pieces—and much was of the highest quality. The discovery of diamonds in South Africa, the gold rush in the States and Australia, the theatre, war, archaeology, the latest ‘Novelty’, all were sources of inspiration for the jeweler. Nineteenth Century Jewellery both describes in absorbing detail the beautiful and sometimes bizarre ornaments of an extraordinary era and tells us much of the craftsmen who made them and the people through whose hands they passed: women of taste and fashion, shopmen, peddlers, confidence tricksters. It is probably the first book on the subject to cove the whole of Europe comprehensively.

The Revolutionary, Napoleonic, post Napoleonic, mid-century, Second Empire, High Victorian and Fin de Siecle styles of jewellery are all pinpointed and analyzed. And there are also useful chapters on the Arts and Crafts Movement, on Art Nouveau, peasant and mourning jewellery and on collecting, and an appendix of the gold and silver marks of ten countries. The development of the great centers of manufacture both in Europe and America is clearly traced. The selection of pieces illustrated is unusual and arresting.

Peter Hinks is Sotheby’s leading expert on nineteenth century jewellery.