Tuesday, October 13, 2009

Gemstone Grading

Various methods are used to describe the quality of a particular gemstone relative to other gemstones of the same type. There isn't any universally accepted grading system. Different dealers often use different methods and symbols to describe the grade of a gemstone. Many use "commercial", "good", "fine" and "extra fine" to describe the stones. You will also often see "AAA","AA","A","B" etc. Grading is always subjective but if done consistently and honestly it should help you compare different stones with different prices. The grade of a stone should take into consideration the color of the stone, the clarity and to a lesser extent, the cut.

Color is the most important consideration for colored gemstones. There are 3 factors affecting the color of a stone. They are Hue, Saturation, and Tone.

Hue is the color of the stone: red, yellow, blue, etc. Generally, the more pure colors are more desirable. For instance, a red ruby is better than a orangish-red ruby. But tastes and fashion trends vary and change. People in different countries and cultures often have different ideas about what color or shade is most desirable.

Saturation refers to the intensity of the color. Saturation is usually rated from 1 to 6, 1 being grayish or brownish and 6 being "vivid". Generally the more vivid color, the better .

Tone is how dark or light the looks. They are rated on a scale of 0 to 10 with colorless being 0 and so dark as to appear black being 10. The ideal tone is usually in the upper middle range but varies among different species of gemstone.

The clarity of a stone simply refers to how clear it is. The main factor here are inclusions. Inclusions are anything within the stone that interferes with the transmission of light through the stone. Inclusions can be small fractures within the stone, or tiny crystals of other minerals. In many cases there are actually tiny pockets of liquid or bubbles of gas trapped within the crystal structure of a gemstone. To the naked eye they just look like little specks or fine lines. Generally the more included a gemstone is, the less valuable. However there are exceptions and inclusions are more acceptable in some stones than others. For example, natural emeralds almost always have significant inclusions, so they are more accepted in an emerald than in, say amethyst which is commonly very clear.. The Gemological Institute of America has attempted to standardize clarity standards for Colored Gems. They have divided Gemstones into 3 types and have defined the clarity grades for each type.

You can see a chart describing the GIA clarity standards here.

The quality of the cut is also a factor in the grade of a gemstone. A well cut stone will reflect and refract light better and will be more appealing.

In later articles I will discuss each of these factors in more detail, but this gives you an overview of what factors are considered when grading a gemstone.

Monday, October 05, 2009

Amazing, Blazing Ethiopian Opal

I wish pictures could convey how bright the color play is in this Ethiopian opal. I've done the best I could with my limited photographic skills. This is a 1.95ct. stone we recently had cut. It shows broad, bright bands of color in almost any light. Mostly red, green and yellow, but a little violet blue as well. The base is a light yellow color. A lot of the material coming out of the Welo area in Ethiopia is stunningly beautiful and seems stable. Some still have doubts about the stability of most of the opals coming out of Ethiopia, but some are starting to say that the opal from the Welo region may be more stable than Australian opal! Prices are still comparatively very low but that may change in time as more people see this African opal, more cutters learn to cut it properly and more trust is built in the marketplace. You can see more pictures of this opal as well as some Ethiopian opal rough on my website.

Wednesday, September 23, 2009

Gemstone Treatments

The topic of gemstone treatments can be confusing for someone shopping for a gemstone. Many people are surprised to learn that most finished gems being sold today have been treated in some way. But that it isn't necessarily a bad thing. The most common treatments are heating, irradiating, dyeing and diffusion. Many types of treatments are considered acceptable in the jewelry trade while others are not. The important thing is that the treatments are disclosed so that you can make an informed buying decision.

The purpose of a treatment is generally to make a gem more beautiful than it would be without the treatment. Some treatments may make a stone more durable. In most cases the treatment is acceptable if it is permanent, improves the qualities of the gem, is disclosed and is not meant to mislead the buyer.

A few types of gems including garnet, peridot and iolite are not usually treated, but most other familiar gemstones usually are. For instance, most all sapphires are heat treated to improve their color and clarity. Heated sapphires display brighter, more even color that would be extremely rare in a natural stone. Therefore most commercially available sapphires have been heated. That usually means you can a afford a more beautiful stone than you could if sapphires were not heated. Heat treatment is widely accepted in the trade. Most of the amethyst now being sold has also been heat treated to improve the color and make it more even.

Some sapphires receive diffusion treatment to alter their color. Through heat and pressure, a particular chemical element is diffused into the cut stone, thereby changing the color. That' the case with many- of the “padparadscha” (pinkish-orange) sapphire that is on the market. However diffusion only effects a thin outer layer of the stone, so if the stone is scratched a little or chipped the original color will show. For that reason, this is often considered an “unacceptable” treatment unless the buyer is fully aware of the treatment and its risks.

Many people like the idea of having an untreated stone. They feel that part of the attraction of gems is that it is something created by nature, without any human manipulation. They prefer untreated stones even if it is more expensive or they have to sacrifice color or clarity a little. Treatment is so commonplace that untreated gemstones are becoming rare and so, they may have more value to a collector or purest.

Below is a list of some of the treatments that are usually deemed “acceptable” by the jewelry trade:

  • heating sapphires and rubies
  • heating aquamarine, amethyst, citrine, tanzanite, topaz, tourmaline, and zircon
  • irradiating topaz (to make clear topaz blue)
  • putting organic resins and wax in emeralds
  • waxing lapis lazuli, jade, and other opaque gemstones
  • dying onyx black

Many of these treatments are virtually undetectable, so whether or not they are treated is difficult to prove. Many stones are sold as “probably treated” and you should assume the stones you are buying are, unless it is specified as “untreated”. You may see the term “natural used”. The term “natural gem” means that the stone was formed in the earth. In other words, it is not synthetic, man-made or lab created. But it may be treated and can still be called natural!

Here are some of the treatments that are usually considered “not acceptable”:

  • diffusion treatment of sapphire
  • glass filling of ruby
  • epoxy resin in emerald
  • dyeing lapis lazuli blue, or most other dye treatments
  • epoxy treatment of jadeite

Even these treatments are not illegal or even unethical as long as they are fully disclosed. Ultimately, it is a personal decision whether you buy a treated, untreated or synthetic gemstone. The important thing is that you know what you are buying.

Saturday, September 19, 2009

Iolite: Beautiful & Affordable Blue Gem

Do you love blue sapphires or tanzanite but they don't quite fit your budget? Consider iolite! This gemstone is probably not as well known or as often used as it deserves. It is the gem variety of the mineral cordierite.

Iolite Has very pronounced "pleochroism". That means that the color looks different when you look at it from different angles. Because of this property, the Vikings were able to use thin pieces of iolite to navigate, using it to determine the exact location of the sun even in bad conditions. The same stone can look violet- blue or yellowish-gray or even clear depending on how it is viewed. For that reason, it is very important that the stone be properly cut so that when it is viewed face up, you see the best color. Sometimes it is called "water sapphire", although the best colored specimens actually look more like fine tanzanite.

It is mined in Brazil, Sri Lanka and several locations in Africa. It's relative hardness and beautiful color make it a great jewelry stone. And the price is surprisingly affordable. A very nice stone can be had for under $10 per carat. If you dream of some day owning a large tanzanite, but you are still a few thousand dollars short, a nice iolite will make a good place holder in that ring setting for now.
You can see some more iolites here and some iolite earrings here.

Wednesday, September 09, 2009

Rutilated Garnet

You may be familiar with the gemstone rutilated quartz. It is a fairly common stone that can be strikingly beautiful. It is clear quartz that has inclusions of rutile crystals within it. The rutile appears as long, thin, needle-like crystals that are black, gold or often reddish-brown in color. I have occasionally found a rutile inclusion here or there in other types of gems, but usually its just a couple of thin lines in the gemstone and is a detractor from the stones appeal rather than something that enhances its beauty and value. Recently though, I got some faceted grossular garnets from Africa. A couple of them were quite heavily included with rutile. Here's a picture of one. The garnet is a pale green color with a number of gold rutile crystals running through it at various angles. Its very interesting and I think, attractive! Garnets

Tuesday, September 08, 2009

Color Change Garnets from Kenya

I wrote back in January about color change garnets. Now I actually have some in my hand, so I'd like to revisit the subject. Garnet is one of only few gemstones that can exhibit a color change. A color change gem is one that appears to change from one color to another color depending on the light source. The atomic structure of the gemstone reacts differently under the ultraviolet rays in natural sunlight (or fluorescent light) .

I have two different types of material. I have some that are larger stones in the 2 to 3.5ct. range. They have beautiful brilliance and scintillation. The color change isn't 100%. In outdoor light they are a slightly pinkish-brown color but with bright red highlights. In indoor light they are more of a raspberry pink color that reminds me of some pink tourmalines that I've seen. They are really gorgeous stones!

The other ones that I have are the really rare ones that were just discovered in Kenya in the last year. They show a very strong color change from kind of a steel blue in daylight to purple in incandescent lighting. I have 2 of these, both under a carat. These are real collector's items
Follow the link to get more details on some of these color change garnets.

Friday, September 04, 2009

East African Rubies

The world's best rubies have traditionally come from Asia, most notably Burma and Thailand. Africa has long been a source of rubies, but mostly brownish or purplish stones. Most were opaque or heavily included. In recent years however, there have been several finds of ruby deposits in east Africa that are a beautiful red or pinkish-red color. Although most are best suited to cabochon cutting, some have facet grade clarity. The biggest producing countries in the are Madagascar, Tanzania and Kenya. I recently obtained some beautiful cabochons that were mined near the Tanzania-Kenya border. Most have some, spots, fissures or other inclusions but the color is fabulous and the prices are great. They are ideal for jewelry artists who would like to add some precious gems to their collection without spending hundreds of dollars on a stone. They are of course very durable and easy to work with. They can even be set and baked in Precious Metal Clay. You can have a look at some of these ruby gemstones here. They are priced from $8 to $100 depending on the size and quality.

Wednesday, July 15, 2009

Ethiopian Opals

For decades, most commercially available opals have, for the most part come from either Australia or Mexico. Occasionally you'll see a precious opal from Brazil and a few come from Russia, Peru and even the United States. Recently we are seeing more and more jewelry grade opals coming from Ethiopia. In the 1990's opal began coming on the market from the Yeta Ridge area. This opal occured inside of ryolite nodules, kind of like little geodes, usually a couple of inches across. Most of the nodules, which just look like roundish, gray rocks, have no opal inside. Most of the ones that do have opal contain just a reddish-brown "potch". But a small percentage will have beautiful, fiery, "precious" opal. It is sometimes orange, white or clear, but often it is a reddish-brown color which usually described as Mahogany or Chocolate opal. It most often has vivid red and green opalescence and looks quite unlike any opal I've seen from Australia.

A couple of years ago, Opal was been discovered in the Gondar Desert region of Ethiopia. It is seam opal, more like what is found in Australia or Brazil. And just in the last few months, opal has started coming from Welo, Ethiopia. It displays very bright, broadflash fire and is quickly becoming very popular.

Ethiopian opal has a reputation for being unstable, meaning that it has a tendency to crack or "craze". As with all opal, some is more stable than others.
But if the stone is properly evaluated, cured and cut you can end up with good, stable gemstones that are truly spectacular! The opal from Welo is supposed to be very stable, but even opal from the same field can vary from piece to piece. Ideally, opal should not be bought or sold until it has had ample time to cure (dry out) after it is mined. Reputable miners will quarantine the material for a number of months to make sure that it isn't going to craze when fully dry. Great care must also be taken when the material is cut. If it becomes overheated in the cutting process it will crack. But if you buy your stones from a reputable dealer and handle them with reasonable care, they should be fine.

Ethiopia is producing a great variety of opal for jewelry and collectors. There is some beautiful Ethiopian, orange, fire opal that looks just like Mexican fire opal. I have seen base colors of white, yellow, clear, brown and orange with a full spectrum of fire colors. There are also "contra luz" opals from Ethiopia which show no fire when viewed from some angles, but vivid color when light hits them from the side. Some of the opal from Ethiopia is called "hydrophane" opal. Hydrophane, when it is dried out is opaque, usually white. But if soaked in water it becomes transparent!
Cut and rough Ethiopian opals for sale

Friday, May 29, 2009

Merelani Mint Garnets

Many people don't realize that garnets are not just red gemstones. They come in a great variety of colors. Some of the most sought after have always been in the green family. Demantoid garnets are usually light green and have a diamond-like brilliance. They also can have a diamond-like price. Large specimens are very rare. Another favorite has been Tsavorite. They are a beautiful, rich, emerald green. A new comer among the green garnets is the "Merelani Mint" Garnet.

Merelani Mint garnets are named for the Merelani Hills of Tanzania where they are usually found. They are a close relative of Tsavorites. Both are categorized as grossular garnets. The only real difference is the color saturation. Tsavorites are colored deep green by chromium or vanadium. Merelani Mint garnets are just paler cousins. A few years ago they were often dismissed as lower quality tsavorites, but many people prefer their more delicate, somewhat subtler shade and they have been quickly gaining an avid following. As their popularity has grown, of couse, so has their value. Prices of several hundred dollars per carat are common and I have seen them as high as a thousand dollars per carat for top grade specimens. Like tsavorites, large pieces, over 3 carats are very rare.

Visit my website www.PalmBeachGems.com to see more Merelani Mint Garnets as well as other garnets.

Sunday, May 17, 2009

Opals on a Budget

Opals have been one of the world’s favorite gemstones for centuries. Nothing compares to opals for their fantastic displays of brilliant colors that move and change as the stone moves in the light. The finest opals can rival diamonds in price. Large specimens with bright colors, in sought after patterns can sell for thousands of dollars per carat. Fortunately though, there are beautiful opals available even for those of us on a budget.

One option of course is to sacrifice quality somewhat. You can find opals for under $20 per carat that are still beautiful. The colors won’t be as vivid as the higher priced opals and there may be areas of the stone that show no flashes of “opalescence” but they will still be very attractive stones.

But what if you want a really bright, flashy opal? Another option is to look for an opal “doublet” or “triplet. One reason that precious opal is so expensive is that it often occurs in thin layers that just aren’t thick enough to cut into a gemstone. But these thin pieces of material can still be used to make doublets and triplets! The layer of precious opal is first bonded to a layer of a cheaper stone. Usually ironstone is used. It is readily available in the Australian opal mining regions, it is very hard and it is a dark color. It does several things. It makes the stone thick enough of course plus it makes it. Plus, it gives the opal a dark background which makes its natural colors stand out more vividly! If it is going to be a doublet, it is then cut and polished as would any other opal. If it is going to be a triplet, another layer is first glued to the top of the stone.

This other layer is usually quartz. Quartz is very clear and very durable. So now when it is cut, you have a layer of fiery opal sandwiched between a layer of ironstone and a layer of quartz. The dark backing makes the stone appear more brilliant and the quartz top make it more durable and scratch resistant than a solid opal. But best of all, the prices for doublets and triplets are much lower. You will usually only pay about 10% of the price you would pay for a comparable looking solid opal. So for $20 you can get an opal that looks like a $200 opal. For $200 you can get one that looks like its worth thousands!

There are some cases where the layers may separate over time if not cared for properly. But if handled and cleaned with care, as you should with any opal, they can last a lifetime and you can own the opal of your dreams without spending a fortune.

Wednesday, February 18, 2009

Rich Blue Iolite Earring Studs

Iolite is not a real well known gemstone, but they are beautiful. High grade Iolite looks a lot like sapphire but at a fraction of the price. The mineral name is Cordierite. It is also sometimes called "water sapphire"
These are very nice, gem grade iolites from Kenya. They are set in sterling silver posts. For more details look at eBay item 300294975279

Monday, January 19, 2009

Color Change Garnets

If you were born in January, you probably know that your birthstone is Garnet. Most people think of rich red gemstones when they think of garnets. However through the years garnets have been discovered in many different colors. In fact just about every color but blue. There are emerald green "Tsavorite" Garnets, bright orange "Spessartite" Garnets and even some rare pink garnets. But if you still can't make up your mind there are also "color change" garnets. These garnets appear to be very different colors depending on the type of lighting. Typically they will be a greenish-blue color in sunlight but when indoors under incandescent lighting they will appear a reddish-purple color. They look a lot like Alexandrite which are famous for their color-change properties. All of the color change garnets that I've seen have come from Africa, mostly from Madagascar, Tanzania and Kenya. The prices vary depending on size, clarity and how pronounced the color change is. Top specimens can be $1000 per carat or more.The picture at left is a recently unearthed piece of color change garnet rough weighing 280cts found near the Kenya-Tanzania border.

Sunday, January 04, 2009

Beautiful Coober Pedy Freeform Opal 1.83cts

This beautiful solid opal is now for sale on eBay. It is a freeform cabochon, approx. 17x12mm eBay item #300284853802 end time Jan-11-09 13:06:11 PST