Other Gemstone Treatments-Surface Coating and Fracture Filling

The general feeling among gemologists and gem merchants is that there is nothing wrong with any type of treatment as long as it’s fully disclosed to the customer, and the customer is being charged appropriately for the treated stone.  As discussed in our last blog, many treatments have stable results.  Enhancements such as bleaching, irradiation, and heating are commonly accepted by most in the jewelry industry because, not only are they permanent but they are also treatments that could have occurred naturally. Some enhancements, however, are not as stable or they lack that “natural” quality. Gemologists and gemstone merchants are wary of gemstones that have been coated or fracture filled.

mystic topaz

Gemstones have been painted or coated for thousands of years.  It’s not a new idea.  Often the back side (pavillion) or girdle of a faceted gemstone is coated with a thin film of metal oxide paint.  The well-known Mystic Topaz is actually colorless topaz with a thin layer of titanium on its pavillion.  The coating causes interference with light and leads to Mystic’s rainbow of colors.  Drusy quartz is another gem that can get coated with permanent metallic film, using a process called vapor deposition.   Both of these processes are permanent as long as the gems aren’t exposed to high heat or chemicals.

If a gem such as emerald  has tiny fractures or cavities that reach the surface of the stone, apparent clarity of the gem can be improved by filling the fractures with either oil or wax.  Even diamonds or rubies can be fracture filled, although the filling is generally lead glass rather than oil.   Glass fillings are more durable than oils or waxes.  High heat, acids, or even vigorous cleaning in an ultrasonic cleaner can drain the emerald of its oil.  New oil can be inserted but, until it is, the emerald will look like it has more inclusions than it had before.  Many gemologists worry more about fracture filled diamonds.  Emeralds have been oiled for centuries and bench jewelers know the special care that they need.  But diamonds normally handle the heat of the jeweler’s torch.  A fracture-filled diamond, however, cannot handle heat, and must be treated differently than a non-treated diamond.

Fracture-filled-diamond-before-and-after

This concludes our three-blog series on gemstones and their treatments.  I guess the thought I want to leave you with is, if you’re buying nice gemstones, ask questions.  Especially if you decide to buy off the internet, look at the fine print.  Fracture-filled diamonds are a “fraction” of the cost, but they require special care and will never be as valuable as a diamond that’s not fracture-filled.  Know what you’re buying.

Common Gemstone Treatments–Heating, Irradiating, and Bleaching

The Earth is very hot–over 10000 degrees Fahrenheit at its core.  Over the millions of years that gemstones formed in the earth, some have been subjected to high temperatures.  Interestingly enough, this heat can alter the light absorption of the stone, changing its color.  Sometimes heat “improves” the color of the stone, perhaps taking a gray, brown, or almost colorless stone and turning it to a cheerful blue or a regal purple.

Man has found a way to heat stones that Earth neglected to heat.  The most common types of heat treated gemstones are ruby, sapphire, topaz, tanzanite, and zircon.  If you buy one of these stones, you can be quite certain that it’s been heated by man.  You’d pay a huge premium to have beautiful color without man-made heat.  The time spent heating, the temperature, and the other treatments that may be combined with heat will all vary depending on the raw material.

non-heat treated tanzanite on the left and heat-treated tanzanite on the right

Non-heat treated tanzanite on the left and heat-treated tanzanite on the right

 

Our planet also naturally irradiates stones.  Irradiation can change the arrangement of the protons, neutrons, and electrons that make up the atoms of the stone.  This can alter the color of stones as well.  Man has figured out how to irradiate gemstones in order to improve color.  They can be treated to high energy radiation at a gamma ray facility that uses cobalt-60 so that there is no residual radioactivity.  Diamonds are sometimes irradiated to create beautiful fancy colored diamonds.  Colored diamonds can occur naturally, but it’s rare for them to be blue or green.  That’s why famous gems like the Hope Diamond or the Dresden Green are so amazing.   If you see a blue or green diamond, chances are man has irradiated it.  Blue topaz is another irradiated gem stone.  It’s the combination of irradiation and heat treatment that brings out that beautiful Swiss or London Blue in topaz.

The sun gave us inspiration for bleaching.  Stones often look prettier if they are whiter or less brownish.  Pearls and jadeite are both commonly bleached–and not by the sun. The process involves hydrogen peroxide or some type of acid.  Pearls, even if they are natural in color rather than dyed, are still often bleached to lighten and brighten the color nature gave them.

Unbleached jade on the left and bleached jade on the right

Unbleached jadeite on the left and bleached jadeite on the right

 

Most people in the jewelry industry accept these three treatments.  Since heating, irradiating, and bleaching could have all occurred naturally, it seems that man is helping out by making a natural process accessible to more gemstones.  And since all of these treatments are permanent, no one has to worry about their gemstone changing over time.  Finally, without these treatments, colored gemstones and pearls would be much more expensive and exclusive.

Our final post of this series will be about treatments that are not as commonly accepted.  These are treatments you, as the consumer, should definitely be aware of before you buy.  Treatments such as surface coating and fracture filling can enhance the look of the stone but may not be permanent.  Remember to ask questions if you want to know about treatments on a gemstone you’re planning to purchase.

 

 

 

 

 

Understanding Gemstone Treatments

Paraiba tourmalines photographed from the GIA Collection for the CIBJO project from the Dr. Eduard J. Gubelin Collection.

Paraiba tourmalines photographed from the GIA Collection for the CIBJO project from the Dr. Eduard J. Gubelin Collection.

This blog is the first of a series on gemstone treatments.  The truth is, all gemstones have been modified by man.  We’d like to think that a gemstone’s beauty is completely natural, but the reality is man plays a part.  Cutting and polishing bring out the sparkle and color.  Shaping and setting is all done by man.  So a gemstone’s beauty can be attributed to both man and nature.  Each consumer must decide what level of man’s contribution is acceptable.  Everyone sees that man must be involved to some degree, but opinions vary on enhancements such as irradiation, dyeing, or fracture-filling.  Is there a point where man’s contribution to a gemstone’s beauty goes over the fine line, when the stone just doesn’t seem natural anymore?

Another fine line is the one jewelers walk everyday when conversing with customers about gemstones.  There are laws and guidelines, set by the government and the AGTA (American Gem Trade Association), for disclosure of gemstone treatments.  But jewelers adhering to those guidelines also have to make sales in order to stay in business.  Some customers are truly interested in learning about how gemstones arrive at their beautiful state.  But many would be bored by a lesson in gemstone treatments and might walk away from a sales representative who insisted on giving all the details.  Certainly anyone who sells jewelry should honestly answer customer questions about gemstone enhancements or treatments.  We want our customers to understand as much as they’d like to understand about gemstone treatments.  We want them to understand that, if treatments didn’t exist, most of us would be unable to afford pretty gemstones.

So that’s what the series will be about.  It will give you an overview of some of the main treatments on some of the most common gemstones in the market.  The series will also discuss some gemstones that are not treated–ONLY cut, polished, and set.  If you find this fascinating, I will include some sources for learning more.  And remember, if you want to know more about the gemstone you’re buying, just ask.

If it’s Red, is it Real?

ruby1

Most of us know that not every red gemstone is a ruby.  Garnets, tourmaline, and even diamonds can be red.  But if you are in the market for a ruby, know that many substitutes exist.  I recently put on a seminar about rubies, their imitations, and synthetics.  Let me share three pieces of advice on buying a ruby.

1) Buy it from an A.G.S. member store. Only jewelry stores who adhere to the strict consumer protection standards of the American Gem Society  will have the A.G.S. sign by the front door.  These stores are required to be informed on ethical issues and questionable practices facing the gemstone and jewelry industry.  At least one employee of the store must be a registered jeweler, which requires yearly testing to renew the designation.

American Gem Society

2)  Look at that beautiful stone under the microscope.  All A.G.S. member stores are required to have a microscope at their store.  Ask to look at the piece you’re considering.  If the stone shows some inclusions under magnification, especially whitish or colorless rounded crystals or a lacy-looking fingerprint, that’s a good sign.   Be suspicious of a stone that looks perfect under magnification.  Natural rubies generally have inclusions.  Remember to ask about treatments on the stone.  Most rubies have been heat-treated to improve their color and sometimes their clarity.  Heat treatment is permanent and does not affect the durability of the stone.  If the stone has fractures that have been lead glass-filled to enhance the clarity, it is not as valuable as one that has not. In fact, most gemologists feel that these “composite rubies” shouldn’t even be called rubies because so much of their weight is due to the lead-glass.  Be aware that a glass-filled stone is not durable and should never be subjected to heat or an ultrasonic cleaner.

3) Don’t assume that, because it’s old, it’s real.  Synthetic rubies have been produced since the early 1900s.  Rubies were also imitated using glass, assembled stones of garnet and glass, and other natural red stones like spinel.  Even the “Black Prince’s Ruby” in the British Imperial Crown is actually a 170 carat red spinel!

British Imperial Crown with the "Black Prince's Ruby"

British Imperial Crown with the “Black Prince’s Ruby”

The Gift of Quartz

sand

Is it hard to believe that something as common as sand or dust is made of, basically, the same ingredients as the most beautiful amethyst?  Silica and oxygen are two of the most common elements on Earth, and they are the two needed to form quartz, a group of minerals which contains, among other gemstones, amethyst.  What a gift that, sometimes, the simplest and most common ingredients make an awe-inspiring product.

The “Quartz Family” is a wide-ranging group.  Amethyst is part of the large or single crystal strand of this group, along with citrine, smoky quartz, rock quartz (colorless quartz), and prasiolite (green quartz).  These are the quartz gemstones that are likely to be faceted in order to refract light.  They are more transparent, being cut from a single crystal.  There are two main reasons why these gemstones are different hues.  Trace elements such as iron can mingle with the silica and oxygen to influence the color.  Heat and/or irradiation acting on the mineral can also change its color.  Citrine, for example, is generally made by heat-treating pale amethyst.

Another branch of the quartz group is the microcrystalline strand.  Gemstones like tiger’s eye and aventurine are aggregates of many, many small quartz crystals.  These gemstones are generally translucent or opaque and are rarely faceted.  You might see them carved into cabochons or made into beads.  Colorless quartzite is an aggregate that is often dyed in various colors, sometimes to mimic other gemstones like jade.

Gemstones with cryptocrystalline structure have crystals too small to be seen without a powerful microscope.  Chalcedony, agate, and chrysoprase fall into this strand.  Chalcedony comes in various colors, both naturally and with man’s help.  Chrome chalcedony is naturally green due to a trace element of chromium.  But black onyx is actually chalcedony that has been dyed black.  Chrysoprase, one of the most valuable gemstones in the quartz group, is a translucent apple-green due to the presence of nickel.  These gemstones are sometimes faceted but usually are made into cabochons, beads or other carvings.  Agate, a multi-colored banded gemstone, can be used to carve cameos.

Quartz comes from almost every corner of the globe.  South America, North America, Australia, Africa, Asia, and even Europe all have deposits of quartz.  Because it’s so plentiful, even in large pieces, quartz is generally affordable.  We often think that the more expensive something is, the more beautiful it must be.  But that’s just not true in the case of quartz!

amethyst