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our guide to diamonds and precious  gemstones

Sinclair works with expert gemologists to hand-select diamonds that are guaranteed to be from conflict-free mining regions. Each diamond comes with an official certificate of origin and all diamonds used by Sinclair are subject to the 'Kimberley Process.'


With this process, each step from mining to cutting and polishing, ethical rules are demanded, applied and checked. This is to provide confidence and peace of mind to our discerning clients. Through our international gemstone network we locate the ideal stones by offering our creations at highly competitive prices.

Sinclair gems are 100% natural and certified by the most reputable international gemstone laboratories. We don’t offer lab-created gemstones or simulants.

It’s not just any diamond - each Sinclair diamond is hand-selected and goes through rigorous grading and screening to ensure our guarantee of integrity.

A diamond’s quality is determined based on four main categories better known as the 4Cs, which stand for color, clarity, cut, and carat weight. A white diamond color is considered ideal, when it is as colorless as possible, it is graded based on the absence of color.

Colored gemstones however are graded differently than diamonds, here the main category is the color, mainly because the difference between the two is the lack of color versus the presence of color. 'The big 3' of colored gemstones, such as ruby, sapphire, and emerald are graded by their color, country of origin, their saturation, color uniformity and purity.


The most respected names of international colored gemstone grading labs are Gubelin Gem Lab, American Gemological Laboratories (AGL), Gem Research Swiss Lab (GRS), Gemological Institute of America (GIA), Swiss Gemmological Institute (SSEF) and C. Dunaigre Switzerland (CD).


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the king of gemstones


Diamond is the only gem made of a single element: It is typically about 99.95% carbon. The other 0.05% can include one or more trace elements, which can influence its color or crystal shape. It’s the hardest known mineral. At its place of origin, deep inside the earth for millions of years, carbon was subject to high pressure and intense heat. The result is a mineral which we call diamond.

Even though a rough diamond is impressive by itself, the diamond cutter has the demanding task to discover its unique beauty. To bring out the play of light by faceting the rough stone in precise proportions and angles to disperse the light like a prism so it produces its unique “fire” based on the spectral colors of the light. This unsurpassed sparkle makes a diamond a thing of irresistible beauty and a fascinating object. One needs a diamond to cut a diamond, faceting can only be done with tools which are covered with industrial diamonds. A fully faceted diamond is a captivating gem and - depending of its quality - of timeless and stable value. No two diamonds are identical, even if they look identical to the untrained eye. Every diamond has its unique personality, soul and fingerprint.

The 4 Cs stand for CARAT, COLOR, CLARITY, and CUT. They determine a diamond’s grading, which has an impact upon the value of the stone.

CARAT: The weight of a diamond is measured in carat (ct). It derives historically from the carob seed, which was assumed to have a standard weight. One carat corresponds to 0.20 grams.


COLOR: The less tint - the higher the value. Most diamonds seem colorless, but it requires a specially trained eye to distinguish slightly different color shades and nuances. A precise examination is required to determine, how close a diamond comes to absolute colorlessness meaning top value. The lack of color makes a white diamond more valuable. The only exceptions are “fancy colors” like natural yellow, pink, blue and green diamonds.

CLARITY: Determines, how perfect is the crystal structure. How free of inclusions, growth characteristics, and other marks is the diamond? They are also called nature’s “fingerprints”, and they represent the uniqueness of every single diamond. Grading from internally flawless, to very, very slight inclusions, to very small inclusions, to slight inclusions, to Pique’.

CUT: The cut makes the diamond perfect. Man cannot influence color, clarity and carat weight of a diamond, but the quality of the cut to reveal its true beauty. It means the various proportions, symmetry and polishing of a diamond, which is of crucial importance for its brilliance and thus for its evaluation and valuation. For generations, the cuts have been improved and optimized, in particular the brilliant round cut, to reveal a stone’s maximum brilliance, beauty and fire. Specialty cuts like the Gabrielle cut, or the Flower cut are also offered on demand by Sinclair, the most innovative diamond cuts developed by Sir Gabi Tolkowsky, the legendary diamond cutter of modern times.

THE IMPORTANCE OF THE FIFTH C: It stands for CONFIDENCE and is gaining in importance. The key aspect is respectability and integrity. Trust and confidence are always in the center of our business. In addition to precise cuts, the exact grading according to international standards, fair and honest dealings with business partners are absolutely essential for sustainable success. Never has the fifth C been of such importance as it is nowadays, where color and clarity treated diamonds and synthetics in the trade require competent experts. Sinclair Gems only works with the most reputable and best-known diamantaires in the world, and some of the oldest diamond cutting companies in Europe strictly adhering to the Kimberley process certification scheme.

For all diamonds of 0.50 carat or more, our customers automatically receive a certificate from the diamond testing lab (DPL) and a confirmation in form of a written guarantee of the grading by an officially accredited organization - facts, our customers can rely upon.



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An emerald’s hue, tone and color saturation determine its value. The most desirable emerald colors are bluish green to pure green, with vivid color saturation and tone that’s not too dark. The most-prized emeralds are highly transparent. Their color is evenly distributed, with no eye-visible color zoning. If the hue is too yellowish or too bluish, the stone is not emerald, but a different variety of beryl, and its value drops accordingly. The intensity of the green in the finest emeralds might not be equaled by anything else in nature. Chromium, vanadium, and iron are the trace elements that cause emerald’s color. The presence or absence of each and their relative amounts determine the exact color of an emerald crystal. Emerald appearance is sometimes associated with its mine location. Colombian emeralds, specifically from the famous Muzo mine, are said to have a warmer and more intense pure green color. Zambian emeralds are said to have a cooler, more bluish green color. Emerald inclusions are often described as looking mossy or garden-like. They’re sometimes called 'jardin', French for garden. The trade generally accepts eye-visible inclusions in higher-quality emeralds. But when the inclusions have a negative effect on transparency and clarity, they also dramatically reduce value. 99% of real emeralds are still treated with oil in order to fill cracks within the stone. The rare 1% that are not treated with oil will be clearly marked NO OIL and will demand much higher prices. These are considered the top of the top when it comes to quality emeralds.

 Sources: Colombia, Brazil, Zambia, and Zimbabwe supply the majority of emeralds on the international market. Colombia produces what many consider to be the highest quality and volume of emeralds. The Colombian emerald has been widely accepted as the world’s most desirable pedigree and its famous Muzo mines remain a prized locality to this day.

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A sapphire comes in a variety of colors. It can be a pure blue but ranges from greenish blue to violetish blue. Besides blue sapphire and ruby, the corundum family also includes so-called 'fancy sapphires.' They come in violet, green, yellow, orange, pink, purple, and intermediate hues. The name 'sapphire' can also apply to any corundum that’s not red and doesn’t qualify as ruby, another corundum variety. The rare corundum crystal’s pinkish orange color is called 'padparadscha', named after the lotus flower.


Color has the most important influence on blue sapphire’s value. The most highly valued blue sapphires are velvety blue to violetish blue, in medium to medium-dark tones. Intensely saturated and velvety, rare sapphires from Kashmir set the standard for the finest blue. Preferred sapphires also have strong to vivid color saturation. The saturation should be as strong as possible without darkening the color and compromising brightness. Sapphires with these qualities command the highest prices per carat. The most preferred and most valuable sapphires are deep color saturations known in the trade as 'Royal Blue' and the soft velvety blue called 'Cornflower Blue'.

Top blue sapphire origins:


Kashmir is the most famous source of blue sapphires from the border region between NW India and Pakistan. Kashmir has a long history of mining spectacular blue sapphires that have set records at prestigious auction houses. Kashmir sapphires are most sought after by international investors and collectors due to their rarity. Most sapphires are old stones mostly mined in the 1930s, they have been bought and sold numerous times and yet command the highest prices in the gemstone market! Because of their reputation and the fact that no new material is being produced (civil war in the region), Kashmir sapphires are avidly sought by collectors who are paying almost any astronomical price for it!! Kashmiri blue sapphires are praised because of their mesmerizing finest velvety “Cornflower Blue” hue and minute inclusions. The “the bluest of blue” and a “sleepy quality” which is often being described as “blue velvet” exceptional color and clarity without any heat treatment. The mystical attributes of this stone have enhanced its reputation in the gem market manifolds.

Mogok Burma sapphires are often known as 'midnight blue'. The sapphires from Mogok are the next most sought after and the next highest on the ladder. If compared with Kashmir sapphires, they are darker and more transparent than Kashmir stones with little or no color zoning. Due to limited production, they are also in high demand in the market.

Sri Lanka (formerly Ceylon) sapphires are known for fine quality and are available in almost all colors, although not as brilliant as Kashmir or Burmese sapphires. They are beautiful cobalt blue - think Lady Diana’s engagement ring! Sri Lanka is known for producing the largest sapphires in the world. Ratanapura is an important center for mining and trading. Nonetheless, Ceylonese and Burmese blue sapphires can’t challenge the pinnacle position of Kashmir blue sapphires.

Madagascar sapphires are relatively recent finds, various colors, but mostly heat treated for better color and clarity.

In the United States, the state of Montana has been a leading producer of both blue and fancy color sapphires.


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The vast majority of the world's finest Rubies used in today's high jewelry come from the mines in the Mogok region of Myanmar (formerly known as Burma). Highly sought-after and breathtakingly beautiful, their price per-carat continues to rise and achieve record-breaking prices in auctions. Ruby can command the highest prices of any colored gemstone. The per-carat prices of fine-quality rubies have been rising consistently, many times breaking auction records!

The strength of ruby’s red depends on how much chromium is present—the more chromium, the stronger the red color. Chromium can also cause fluorescence, which adds to the intensity of the red color. For better-quality material, slight differences in color can make significant differences in value. For top-color ruby that’s also free of eye-visible inclusions, the price rises even more. The per-carat price of ruby can also increase dramatically as size increases, especially for better-quality stones.

Historically, the term “pigeon’s blood” described the red to slightly purplish or pinkish red color of rubies with a soft, glowing, red fluorescence. “Pigeon’s blood” is the most sought after color for collectors and investors in finest gemstones.
To accommodate the crystal shapes of natural rubies, the most common shapes of fashioned rubies are ovals and cushions. Round, triangular, emerald-cut, pear, and marquise rubies are also available. But these shapes are rare in larger sizes and higher qualities.

The most renowned rubies, like those from Myanmar (Burma), the Himalayas, and northern Vietnam, typically form in marble. They’re found in layers that are distributed irregularly within the surrounding marble. Mogok is the center of the gemstone trade in Myanmar and traditionally the source for the finest rubies.

With the Burmese Military’s rise to power in 1997, the US started to impose sanctions on imports of Burmese rubies and jade and the import was entirely prohibited. Burma has made substantial progress towards reforms to restore democracy in Myanmar. The lift of the US sanctions in October 2016 has created a tremendous demand for this exquisite gemstone ever since and results in highest prices per carat for rubies. It is now legal to import Burmese ruby and jade to the US.

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