Fall 2000 Gems & Gemology - Gemfrance

Irradiation at doses of 7.6–187 kGy (exposure times
not given) produced various shades of smoky gray; higher
doses produced darker specimens. Following slow heating
(5°/min to 250°C) in air, the resulting colors (according to
increasing radiation dosage) were pale yellow, yellow,
greenish yellow, “olive” green, greenish orange, orange,
and reddish brown. All the colors were stable to natural
light and to temperatures up to 250°C. Greenish yellow
(“green-gold”) and reddish brown (“cognac”) are presently
the two most marketable colors. Thus, with the right
combination of irradiation and controlled heating (and
favorable contents of Fe and Al), it is possible to obtain
marketable quartz in many colors. TL
Radioactivity of neutron-irradiated cat’s-eye chrysoberyls.
S. M. Tang and T. S. Tay, Nuclear Instruments and
Methods in Physics Research B, No. 150, 1999, pp.
491–495.
Highly radioactive cat’s-eye chrysoberyls have appeared in
Southeast Asian markets (see Fall 1997 Gem News, pp.
221–222). The original material reportedly came from
India and was irradiated with neutrons somewhere in Asia
for color enhancement. This article is the first estimate of
the potential health threat of such stones if they are worn
close to the skin (within 0.5 cm). Because no irradiated
stones were available to the authors for testing, they used
an indirect approach to determine the potential radiation
hazard. In this approach, the typical chemical impurities
and their concentrations in three non-irradiated cat’s-eye
chrysoberyls from India (two from Orissa, one from Kerala)
were determined. Then the activities of all the radioactive
nuclides that can be produced by neutron activation from
these impurities, as well as from the constituent elements
of chrysoberyl (O, Be, and Al), were calculated. On the basis
of the activities so obtained, the radiation dose that would
result from an irradiated cat’s-eye chrysoberyl with these
chemical characteristics was estimated.
Of all the radioactive nuclides that could be created by
neutron activation (based on a 1 ct stone with ~1% Fe),
only four— 46 Sc, 51 Cr, 54 Mn, and 59 Fe—would not have
“cooled down” to the internationally accepted level of specific
residual radioactivity (2 nCi/g) within a month after
irradiation. Three of these— 46 Sc, 51 Cr, and 59 Fe—would fall
to the safe limit in about 15 months; 54 Mn would remain
above the safe limit for seven years. Clearly, such a hypothetically
neutron-irradiated stone presents a significant
health hazard. Because of the compositional variability in
chrysoberyls from different localities, others may be either
more or less radioactive after neutron activation. KSM
Verneuil synthetic corundums with induced “fingerprints.”
J. Free, I. Free, G. Brown, and T. Linton, Australian
Gemmologist, Vol. 20, No. 8, 1999, pp. 342–347.
Flux-healed, quench-crackled Verneuil synthetic ruby and
sapphire are being produced in Chanthaburi, Thailand.
First, the Verneuil boules are heated and then plunged into
water to generate the quench-crackled effect. After the
boules have been cobbed to yield small facetable fragments,
these pieces are heat treated in an unspecified colorless
flux for two days in a kerosene-fired kiln. The
process is completed with a one-day heat treatment in an
acetylene-fired kiln. The key identifying features are
curved color banding or striae, a “checkerboard” pattern of
flux-filled fractures, and increased transparency to shortwave
UV radiation. RAH
MISCELLANEOUS
Carving out a future. Basel Magazine, No. 7, October
1999, pp. 33–34.
Although Idar-Oberstein has traditionally been the ultimate
center for gem carvings, it recently has fallen on difficult
times. The decline of the Asian and Middle East
economies has weakened their markets for gem carvings.
Another contributing factor is competition from Hong
Kong and mainland China. Nevertheless, Idar-Oberstein
is encouraged by emerging new markets in Europe, the
U.S., and once again Asia. These markets, which appreciate
Idar-Oberstein’s craftsmanship, are being created by a
new generation of connoisseurs with different tastes.
Today, potential buyers include not only sheiks and
the traditional wealthy, but also technology moguls.
Recognizing that the newly rich from the technology sector
may not be as appreciative of traditional carving styles,
some Idar-Oberstein carvers are creating items that are
entirely different from anything done before. Interviews
with four successful carvers in this arena indicate the following
preferences by current buyers: carvings with a
matte instead of a highly polished finish; sweeping, soft
styles characteristic of Art Nouveau; and classic-antique
themes inspired by ancient Egyptian and Greek motifs to
which a modern touch is added.
Idar-Oberstein still maintains its reputation as the
world’s leader in fine carvings, and it also has access to
unrivaled stocks of rough. Ultimately, though, it remains
to be seen whether the region can succeed in attracting a
new generation of carvers while maintaining its heritage
of superior craftsmanship. JY
290 Gemological Abstracts GEMS & GEMOLOGY Fall 2000