Recent television presentations have raised the issue that some gemstones
may have been through a treatment process to enhance their
appearance. We want you to know more about those procedures and how they
affect your gem's look and value.
The treatment of a gemstone to improve its looks is nothing new. If fact, some of the earliest published
manuscripts detail instructions on how to improve the color and clarity of
various stones. Papyrus Gaecus Hulmiensis listed instructions about
gemstone enhancements in a treatise dated 400 AD. And C. Pliny's "Natural
History" published in 1548 goes into great depth about such procedures. It should be pointed out that even the cutting and
polishing of rough mineral specimens into a faceted gem is a form of
treatment.
The ancient treatments described were very basic, and by today's
standards almost comical. The early procedures ranged from feeding
pearls to a rooster, and letting it pass through his digestive system to
improve the pearl's color, to boiling gemstones in garlic oil to aid
in removing inclusions. Although these techniques were very basic,
variations of many of those antique practices are still used today,
although in a more scientific manner.
Of all the assorted treatments, there are three basic treatments that you should know about prior to selecting a gemstone for purchase. Heating, sealing, and irradiating are the primary methods used by the
modern jewelry industry to enhance the appearance of a gem.
Heat Treatment
Long ago, miners discovered that if a rough piece of gem
material was tossed into the fire and left overnight, the color would often
improve. Usually this color improvement was accompanied by severe heat
fracturing of the stone. They soon discovered that by placing the
stones into a clay pot filled with mud, the heating and cooling process
occurred gradually, and the stones were much less likely to fracture. Today
gemologists use kilns, like the furnaces used by a ceramics worker, to heat
treat gems. Computer controlled thermostats on these ovens are adjusted
to bring the stone slowly up to the desired temperature, then return the
temperature slowly back to normal. In some high-tech furnaces the oxygen in
the kiln is removed and replaced with special gasses to increase the range
of alteration in the stone being treated.
Aquamarines, for example, are heated
to reduce the green hue in the gem, but the heating does not deepen the
level of blue. Dark blue or black sapphires are heated to lighten their
color to a more pleasing shade of blue. Pale colored amethysts are heated
and turned yellow, to be sold as citrine. Greeninsh-gray zosites are heated
to turn them into Tanzanite. All of these changes can make significant improvements in a stone's appearance, creating gems with wider market appeal.
Heat treating typically causes a permanent change in the stone's color,
and the gem should not require any special handling on the part of the
owner thereafter.
Fracture Filling
The sealing of a gem is an attempt to fill tiny cavities or cracks that
break the surface of the polished stone. In earlier times sealing was done
with grease or wax, and then later with natural hardening oils, such as the
oils used to finish wood furniture. Of these early treatments the only
one still used in any significant measure today is oiling, a
process which is still widely used on emeralds. Advanced sealing methods came
into use when the dental industry began to use epoxy sealers on teeth to
help prevent cavities.
High-tech, epoxy sealers are relatively durable, and can be used to
fill larger cracks or craters on a stone's surface. The typical method is
to place the stones in an epoxy liquid, then pressurize the container to
drive the epoxy deep into the cracks. After removing the stone
from the epoxy the surface is wiped clean, then painted with the catalyst
to harden the epoxy which remains in the cracks or crevices of the stone.
These pressurized treatments can make dramatic improvements in the clarity
of a gem, and in the case of emeralds, to create desirable
gems, at affordable prices. In the case of lapis and turquoise, without some
type of surface sealer these stones would be of marginal use in jewelry -- they could easily become stained by even hand soap or lotions if used for
jewelry in their unsealed form.
Irradiation
Irradiation is the treatment which has no ancient history in the gem world.
The use of linear accelerators operated by scientists can make complete
changes in a stone's color. Blue topaz is mined from the ground in either a
clear, or undesirable brown color. After some possible heating, the topaz
material is irradiation treated and turned into one of several shades of blue.
Near colorless Kunzite can
be turned into intense hot pink colors, and tourmalines into vivid shades
of red or pink. On some gems the effects of irradiation treatment may not be permanent. In the case of
kunzite, exposure to direct sunlight for several weeks can turn a vivid colored stone
back into a near colorless gem.
One last treatment you should know about is surface coloring. Lapis, turquoise, pearls and some additional opaque gems can be dyed to deepen, or change their color. Diffusion treatment, the melting of a thin color layer onto the surface of colorless sapphire, can
result in a gem of fine appearance, but with a clear center. A small chip
or scratch in these diffusion stone reveals their clear center.
Don't always expect your gem sales person to be fully knowledgeable of, or
completely willing to disclose the variety of treatments a gem may have
experienced. An informed buyer is the best customer
