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Mary Posani/MEDILL

How jewelry is made.     


Buying a gem: Let science make you savvy

by Mary Posani
Feb 13, 2013


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Mary Posani/MEDILL

A completed diamond ring.

Why is that glittery pair of diamond earrings so expensive? Should you buy a gold or silver setting? And are the bargains the real thing? Fear not: science can walk you through the choices.

That diamond or gem may sparkle in the right light, but its scientific components justify whether you pay $100 or thousands for it. Experts from family-run Professional Gem Sciences Laboratory in Chicago say the science of gems can make you a more savvy buyer.

“The first questions should be ‘is this genuine?’” said Eitan Tashey, a gemologist from the lab who conducts full jewelry examinations. “There are so many simulants and so many synthetics on the market for every kind of gem today - from glass to much more complex and complicated forgeries.”

With today’s technology, many labs are able to synthesize or alter a gem with a strikingly similar chemistry to the stone they are emulating. Tashey said there are several tests to know if the gem is natural or not:

• Microscope. Gemologists are trained to find the tell-tale signs and characteristics of natural stones. By simply looking under a microscope, a gemologist can easily decipher between natural and synthetic inclusions in the stone.

• Spectrophotometer. A spectrophotometer gauges a light spectrum shining from the gem. A white light has a perfect rainbow spectrum. When the white light shines through a gem, it produces a signature light spectrum that indicates the type of gem and whether it was treated.

Gem treatments affect value

Many gems undergo some type of treatment - whether its color or clarity alterations. Some treatments are more invasive than others, which can drastically impact the value.

Myriam Tashey, co-founder of the laboratory, said a gem that has received no treatment is a premium and going to cost much more than treated stones.

“For unheated, untreated merchandise, it is always a minimum of 30 percent higher than its counter partner of treated merchandise,” Myriam said.

When gems, such as rubies and sapphires are mined from the earth, they are not immediately ready for the retail market and often look jagged and dull. Manufacturers are able to manipulate the stones by putting them in a clay pot and heating the pot in a kiln-like heater. After heat treatments, the gems become more vibrant in color and more appealing for a buyer but is somewhat reduced in value.

Compared to diffusion treatments, heat treatments are minimally invasive. Diffusion treatments are more complex, such as inserting colored glass to enhance the color or diffusing metals such as beryllium to create a pattern in the stone.

For example, a natural ruby with perfect natural color weighing 8 carats can be valued at tens of thousands of dollars. A glass diffusion treatment can make a lesser quality ruby look brilliant but that treated ruby, weighing the same amount, may cost a buyer as little as $100-$200.

Stone needing those treatments decrease the buyer's cost by 50, 60 or 70 percent, Myriam said.

Other treatments can enhance the clarity of the stone without reducing the value. Laser treatments can bleach out crystals grown inside the stone and make the gem clearer. Filling treatments use an oil or polymer to alter the clarity of the diamond by filling in gaps.

“The clarity enhancement process fills an already present crack or fissure with a foreign substance,” Eitan said. “The purpose of this procedure is to actually reduce the optical visibility of those fissures. Unlike laser drilling, the substance filling the cracks will leak out over time.”

Metals impact value too

The type of metal that supports your diamond can determine what you pay and even what you pay to repair it.

Gold prices have skyrocketed. Despite gold’s appeal and value, it is naturally a very malleable metal. The carats of the gold plays an important role in its durability. Fourteen karat gold is more than 50 percent gold and is more durable since it is mixed with other metals. Twenty-four karat gold is 100 percent gold, and is much softer. But a few karats don’t always mean such a drastic change.

“There’s not much difference between 14k and 18k. Both are very durable,” Eitan said. “When you get up to a higher caratages, certainly 22 or 24, your gold is very malleable. That’s at the point of which you should be very careful with jewelry.”

Silver is also a soft and malleable metal. Much of silver jewelry is mixed with other metals, which makes the silver stronger. Sterling silver, which is used for many pieces, is 92.5 percent silver but even a small percentage still helps, Eitan said.

A gemologist report discloses the results of a full examination of a piece of jewelry, analyzing both the metal and the gem. Myriam and Eitan both suggest asking the jeweler for a report before making a purchase.

“My advice is know your budget,” Myriam said. “Are you looking for big flash, little cash? Know what you want, go with a purpose and have realistic expectations.”