gems, corundum, Myanmar.12, Burma.12, Mong Hsu

Smoke treatment is a long-recognized method used to darken the body colour of opal and enhance its play of colour through increased contrast. With careful observation, this treatment can be identified using visual and microscopic features. The following case study documents a particularly clear example. Recently, a parcel of both white and black opals was submitted to the laboratory, declared by the client to be from Ethiopia. All displayed a play-of-colour effect, with the black opals being particularly striking as the vibrant colours stood out against the dark background (Figure 1). Upon closer examination, several features in the black opals drew the authors’ attention. Numerous small, mottled black spots were present throughout the stones. These dark discolourations appeared most prominently around small pits and scratches on the surface (Figures 2 and 3).

gems, corundum, Tanzania.12, spinel, tanzanite, zoisite, Merelani, Mahenge, Tunduru

In a parcel of over thirty rubies from Myanmar’s Mong Hsu mines, all of the stones contained zoned clouds of cottony ‘silk’, believed to be diaspore, as seen in the sample shown in Figure 1. However, this stone stood out from the rest of the lot. In addition to the wispy diaspore silk, it also contained several bands of fine, intact silk needles, likely rutile (Figure 2). It was, in fact, the only stone in this suite to contain this type of silk. While rutile silk needles are uncommon in Mong Hsu rubies, they have been reported on rare occasions, and we have also observed them in a few samples from our laboratory’s reference collection. It is worth noting that despite the intact silk needles, this stone was determined to have been heated. Supporting evidence included other inclusions, such as melted fingerprints, as well as a clear 3309 series with 3232 in the infrared spectrum and zoned chalky short-wave ultraviolet fluorescence. This serves as an important reminder that the presence of intact silk needles does not always indicate that a stone is unheated.

gems, corundum, treatments.6, oiled ruby, oiling

gems, corundum, Burma.12, treatments.6, Mogok, ruby, heat treatment, inclusions.5

Detection of heat treatment below 1200°C in ruby and sapphire can present challenges to gemologists, as alterations to the material are often subtle. In this study, the authors heated Burmese ruby samples from Mogok, Myanmar, at temperatures ranging from 600° to 1500°C. The samples were documented using macrophotography, photomicrography of inclusions, ultraviolet fluorescence imaging, and spectroscopic analysis (Raman, ultraviolet/visible/near-infrared, and infrared) to record any changes, with a focus on features that could help detect heat treatment. A wide variety of solid inclusions, including calcite, mica, spinel, and zircon, were found in Mogok ruby. Many of those were found to be sensitive to heat treatment with regard to morphology and phase transition; their reactions varied depending on a number of factors such as size, distance from the surface, and species. Microscopic examination provided useful visual indications of heat treatment, even at lower temperatures. Raman analysis of calcite and spinel inclusions also proved valuable in providing complementary evidence of low-temperature heat treatment.

gems, corundum, treatments.6, Sri Lanka.12

In recent years, one concern our laboratory has heard from clients and from other gemologists is the issue of color stability in corundum. Some sapphires, particularly those with a strong yellow component (including padparadscha sapphire), contain unstable color centers that may fade when the stone is exposed to light and/or heat (K. Nassau and G.K. Valente, “The seven types of yellow sapphire and their stability to light,” Winter 1987 G&G, pp. 222–231). We regularly test for this in the laboratory by conducting a fade test. Most of the sapphires we encounter that have an unstable color are unheated stones. Recently an orange sapphire of approximately 10 ct was submitted for testing (figure 1). Microscopic examination revealed signs of heat treatment, with partially dissolved silk, several glassy discoids (figure 2), and melted crystals (figure 3). A fade test was conducted by placing the stone approximately 5 cm under a 120-watt incandescent spotlight for at least an hour, and a dramatic difference was observed. The color had changed from orange to a vivid yellow (again, see figure 1). Under normal conditions, high-temperature heat treatment (at least 1200–1300°C) will bleach any color centers that might be present. This suggests that the orange color was activated after the heat treatment. It is possible that this occurred either by subjecting the stone to artificial irradiation or by placing it in sunlight (Nassau and Valente, 1987). However, we are unable to state definitively what process was used to activate the orange color. Several weeks later, we tested another yellow sapphire of approximately 18 ct (figure 4). In this instance, the stone’s features were consistent with those of unheated sapphire. Again, a fade test was performed with the 120-watt spotlight, which mildly warmed the stone to approximately 100°C. Its color also faded after the fade test, and the owner was informed. The owner explained that they had previously put the sapphire in direct sunlight, which would have brought the color back to what was likely its stable state, a process described by Nassau. To test this, we placed the stone in direct sunlight for 30 minutes, and the more intense yellow color did return. Unfortunately, placing the gem in direct sunlight behind a window in our office did not have the same effect. Upon seeing the color return after being placed in direct sunlight, we decided to try another fade test, this time using a light source that would not warm up the stone. An XD-300 xenon light source was used, and the stone was placed within 5 cm of a fiber-optic light guide connected to this source. After exposure to this cooler light source for over an hour, the color did not fade. This suggests that the mild heat of the 120-watt spotlight, not just the light, faded the stone’s color and that the more intense yellow color displayed after exposure to sunlight could indeed be considered the stable color. We have since adjusted our fade tests to be light-only by switching to this cooler light source to avoid the heat generated with the 120-watt spotlight. Our experience with these sapphires has been a fascinating case study in the color stability of yellow sapphire. This example reinforces the importance of considering all possibilities when testing stones in the laboratory. We do not fully understand the exact causes of these changes, and much remains to be learned.

gems, corundum, inclusions.5, Sri Lanka.12

One of the beauties of working with gemstones is that each time you peer into a stone, you get a glimpse of the universe held within. When we first examined the scene in a star sapphire (see above), we were delighted with the view. A feature that immediately stands out is the triangular crystal, which displays terraced growth features and iridescence on the surface when illuminated with a fiber-optic light. Analysis with micro Raman revealed that this crystal is apatite. What makes the scene even more stunning is the way the crystal seems to float over a cloud of rutile silk. This same silk is what creates asterism in the stone. While in this case the apatite crystal resides in a sapphire from Sri Lanka, apatite has also been reported in corundum from a variety of sources, including Afghanistan, Cambodia, Madagascar, Myanmar, Nigeria, Pakistan, Tanzania, Thailand, the United States, and Vietnam. Apatite can be found not only in ruby and sapphire from different origins, but also in many other types of gems. In our laboratory, we have encountered apatite inclusions in emerald, spinel, and garnet. Apatite is a relatively common mineral, so it is not surprising to find it so often as an inclusion. Although it may occur frequently, in this instance it is anything but mundane.

gems, corundum, Thailand.12, treatments.6

A large black star sapphire was brought in for testing. Two large pits on the base were carefully filled with brown dopping varnish. After removal of the varnish with alcohol, it was found that a large portion of the base had been filled with a lead glass.

gems, gemology, ruby, sapphire, jade, inclusions.5, corundum, garnet, quartz, China, Tibet, Thailand, Burma, Myanmar, Sri Lanka, Inner Mongolia, India, Madagascar, Mozambique, Tanzania, Rwanda, East Africa, Greenland

From the dawn of time, precious stones have both attracted and fascinated humans in ways that few other items could. For while objects of desire are found throughout the natural world, physical beauty is too often ephemeral. From the allure of a man, woman, flower or butterfly, through the fleeting moments of a sunset, there is little that lasts and practically nothing that can be passed down to our descendants. The exception is precious stones. Not only are they the most durable creations of Mother Nature, but their visual splendor is truly eternal. This book presents a completely fresh approach to the subject. Dubbing it humanistic gemology, the authors take readers around the world, showing the places they have explored in their search for gems, along with the people and cultures encountered along the way. Within this volume, remarkable photographs of the human world are interwoven with images of the microscopic realm of the gems themselves. In a lifetime beset by time control, where living is broken into ever smaller bits, as you browse through these pages suddenly you plunge into a domain of frozen time, one that affords vistas of millions or even billions of years. For jewels offer not just superficial beauty, but a window on the primordial forces that birthed both our planet and universe. Inside Out – Gemology Through Lotus-Colored Glasses represents a fascinating new direction for gemology, linking the external and internal worlds of precious stones for the first time.

gems, zoisite, tanzanite, treated tanzanite

Over the past five years, gemologists at Bangkok’s Lotus Gemology have seen increasing numbers of what we might call “non-traditionally” oiled gems. This is particularly true of, but not limited to, Burmese gems such as ruby, sapphire, and spinel. But it is important to note that any gem with surface-reaching fissures can be oiled, often with dramatic improvements in apparent clarity. Cuprian and rubellite tourmalines are also frequently enhanced in this way. Recently we received a faceted tanzanite weighing more than 100 carats for testing. As is our practice for non- emeralds exhibiting fissure-filling clarity enhancement, we photograph the gem and then allow the client to re-submit the stone after filler removal. Figure 18 clearly shows the dramatic effect that fissure filling with oil/resin can have on gems such as tanzanite, even where the refractive index of the filler does not closely match that of the gem.

gems, corundum, ruby, sapphire, books

A discussion of the literature of ruby and sapphire (corundum), with particular emphasis on the most collectible books covering ruby and sapphire around the world.