impurities

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The Letseng mine in the small Kingdom of Lesotho, South Africa has just uncovered another massive diamond rough: a 198-carat stone, roughly the size of a large letseng 198 caratstrawberry.

A diamond over 100 carats is rare enough – with only about 10 to 15 found each year worldwide – but a rough that is nearly 200 carats is an exceedingly rare find. A stone of this size is expected to yield a polished diamond around 100 carats, or half the weight of the rough it originated from.

Even though the stone’s size is impressive, it is not even close to being the largest ever uncovered from the Letseng mine. In fact, the Letseng mine is well-known for churning out large, quality rough over the years, and has the highest price per carat production of all the mines in the world. Some of the largest include the Letseng mineLesotho Promise, the 15th largest diamond in the world at 603 carats; the Letseng Legacy at 493 carats, and the Leseli La Letseng at 478 carats which are 18th and 20th largest respectively.

What makes this rough even more valuable is its’ designation of Type IIa, which constitutes less than 2% of all natural diamonds. Type IIa diamonds have no measurable nitrogen impurities, making them chemically pure. This not only gives them exceptional optical transparency, but also a high likelihood of achieving a colorless (D-E-F) grade and a high clarity grade. Officials from Gem Diamonds Ltd, which own the majority stake in the Letseng mine, confirmed this after inspection of the stone noting it as “an exceptional white, high-quality diamond that displays no fluorescence”.

Martin Potts, a London-based mining analyst has estimated the 198 carat stone to fetch somewhere between $12 to $15 million.

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RubyRuby is the birthstone of July and to commemorate it Elizabeth Taylor’s beautiful ring was auctioned at Christies late in 2011. She had a whole collection that hit lots of record-breaking numbers including the 8 carat ruby diamond ring which was a Christmas present given to her by her husband Richard Burton in 1968. Burton had promised the ring to be a “perfect” ruby.

A ruby is symbolized with deep passion and love, that being said it was very appropriate for Burton to promised Taylor a special ruby for their marriage. He is said to want a ruby with the perfect red colour. “But it has to be perfect,” he warned. He was true to his promise and tucked a small box in the bottom of her Christmas stocking. The box went unnoticed at first because it was so small. Taylor commented on the stone saying “It was the most perfect coloured stone I’d ever seen.”

A ruby is red corundum all other corundum’s are referred to as sapphires. Corundum is a form of aluminum oxide; it is naturally clear but can have different colours depending on impurities. Corundum’s are admired for their harness a 9.0 on the Mohs scale. A diamond tops the scale with a rating of 10. Quality hardness with a rich colour and silky shine makes a ruby so valuable. It is formed in places where two continental plates collide such as Central Asia. Ruby is named after the Latin word “ruber” for red. A ruby is one of the most expensive gems. Rubies can range in colour form pinkish to orangey and purplish to brown. The most desirable colour is a so-called “pigeon’s blood,” a pure red with a hint of blue. When buying a ruby colour is the most important feature along with clarity.

RubyThe bidders at the 2011 Christie’s auction agreed and the ruby sold for $4.2 million and set a per-carat record for a ruby at $512,925. In total Taylor’s collection of 80 pieces sold for $115.9 million which was an auction record.  Other records set during the sale were the highest price ever paid for a pearl jewel at $11.8 million, the highest price per carat for colourless diamond $8.8 million, highest price for Indian jewel $8.8million, highest price for an emerald jewel at $6.6 million and the highest price for natural pearl earrings $1.9 million.

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Sapphire HeatSapphires come in every colour except a certain shade of red called a ruby. There are several different methods to enhance and improve the colour and clarity of a sapphire. Commonly practiced treatments are heating a natural sapphire to heighten the look of the stone. Heating a sapphire is done by placing it in a furnace at temperatures between 500 and 1800°C for several hours.  Another way is by heating it in a nitrogen-deficient atmosphere oven for seven days or more. With this process the stones become bluer and lose some of their inclusions like the silk kind. When higher temperatures are used the stone loses all silk inclusions and under magnification the stone is clear. Sapphire and other gemstones being heat treated goes back to Roman times. An untreated natural stone is somewhat rare and will be sold with a certificate from a gemology lab.

Another treatment is diffusion to add impurities to the sapphire and enhance the colour. A type of chemical element called beryllium is diffused into the sapphire with very high heat. Many colours of sapphires are being treated with beryllium. At first orange sapphires were created with this process but now the process has been advanced and many different colours can be produced.

Sapphire Heat

On the other hand a type of sapphire called “Yogo” sometimes does not need to be heat treated because of their natural cornflower blue colour. These sapphires have a deep blue uniform clarity and are generally free of any characteristics or inclusions. Intergem Limited started marketing the Yogos in the 1980’s as the world’s only untreated sapphire guaranteed. By 1982 heat treatment became a major issue at that time 95% of all the worlds sapphires were being heated to bring out their natural colour. The guarantee of Intergems marketing of Yogos set them apart of many in the gem industry. The issue ended up on front page of the Wall Street Journal in 1984 with the headline “Sapphire Marketer Upsets the Gem Industry.”

How to tell if your sapphire has been heat treated? Usually a small UV lamp can help check the gem quickly for any potential alterations. Any stones that have a chalky florescence are most likely heat treated. Taking it to a certified gem dealer with GIA industry standards is a good way to have them test it.

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3: STONE:

Here we will only consider diamonds. If you are considering other stones, speak to a gemmologist to find out your options and get their recommendations. Remember: knowledge is power, know as much as you can about what you are spending your money on.

Diamonds are rocks that form naturally in the earth, so there is no ‘one size fits all’. It is like choosing between apples – size, sweetness, crispness, juiciness are categories you want to balance when picking an apple. It is similar for diamonds but with different criteria.

  • Carat: In gold this word refers to the purity, with diamonds it is the weight/size. Bear in mind that diamonds are priced per carat digitally. In other words 0.5-0.99 is one price bracket, and 1.00-1.49 is another. Therefore it is possible to buy a 0.98 for the price of a 0.5 and it will look like a 1 carat. The other factors are also critical, however, so bear in mind that a 1 carat diamond can vary in price dramatically depending on the other variables.
  • Clarity: Being an organic material, most diamonds have impurities known as inclusions. Inclusions are usually white or black and some can be seen with the naked eye. A stone without inclusions is called ‘flawless’ and carries a high price tag. Clarity is graded using letter-number combinations. For most rings the range to look for is either VS1 and VS2 which are very clear, then S1 and S2 have inclusions that can easily be seen with 10x magnification, but not so easily with the naked eye. Diamonds also possess blemishes such as tiny cracks which can make the diamond cloudy (see warnings below).
  • Colour: diamonds vary in colour from colourless to brown and even black. Unless you are after a diamond that is noticeably coloured, you want to aim for as white as possible. Colour is graded using letters. D is colourless, through to zyx (noticeably tinted). Aim for D-G range for a quality diamond.
  • Cut: this determines the overall shape of the stone (round, square, rectangle, oval, pear shaped etc) and sparkly (fire). The more facets the more the light is bounced around in the stone and is reflected back to you as sparkle. Round brilliant cut is the most popular and gives a lot of sparkle. Also more facets can hide impurities, for example, if you are in the market for a flawless diamond, this will be well seen in an emerald (rectangle) cut.

Speak to a jeweler who knows their stones. If your priority is high purity, then maybe you can go down on the carat size or colour etc.

WARNINGS:

Not enough emphasis can be made on the importance of buying from a reputable retailer. It is really important that you trust who you are buying from as not all jewelry is what it seems.

  • Castings of the ring mounts when machine made can be porous (tiny bubbles in the metal); the claws that set the stones can be loose, and these rings will not last.
  • There are imitation diamonds on the market, so be sure to get a certification so that you know you are not buying a cubic zirconia or moissanite when you want a diamond.
  • Especially when buying jewelry unseen, such as on the internet, be aware that even if the dealer is obliged to state colour, clarity and carat value, it is not obliged to state cloudiness or treatments that have been made to artificially enhance the stone. These include laser drilling where tiny pin holes are made into the inclusion to bleach it white or dissolve it. These can look like natural flaws and don’t necessarily impair the appearance or structure of the stone. Fillers, however are not considered permanent and the substance used (usually glass) has different properties to diamonds and can appear as colour flashes unusual to diamond. Also, heat and sunlight can effect this substance over time darkening or eroding it. Even though diamond is the hardest substance, cracks (especially unfilled) are weaknesses and make the stone vulnerable to cracking. There is nothing wrong with buying a treated stone (it can make a lesser quality stone appear better), but make sure that this is disclosed when you purchase so that you know you are paying the right price.

You are now armed and ready to browse those jewelry stores and know what you are looking at! This is all very technical information, as you browse you will find that some diamonds “speak” to you more than others. Don’t be held down by the numbers – find a stone you love and a setting that compliments the stone and your personality. And shop around for the jeweler you trust.

Happy shopping!

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