1. POLISHED DIAMOND GRADING STANDARDS

Even though the rules for polished diamond grading are very similar throughout the industry, the process towards their standardization is still continuing under the joint effort of the International Diamond Council (IDC) and the World Jewellery Confederation (CIBJO). The efforts to standardize the polished diamond grading are summarized in the latest issue of IDC Rule Book.

When dealing with an already grade diamond, there are many gemological institutes and certification authorities worldwide. The most professional and reputable polished diamond grading organizations in the world are currently the Gemological Institute of America (GIA) and the Hoge Raad voor Diamant (HRD) Antwerp. When learning about diamond grading, the very essential, and frequently described, characteristics are the 4Cs, representing the Color, Clarity, Cut and Carat Weight of a diamond. Below are some of the many useful links to the topic of 4Cs as issued by the above mentioned organizations.

2. THERE'S NO KARAT LIKE CARAT...

Difference between carat (ct) and karat (kt)

The same word, even though with a different spelling, is used to describe the weight of a diamond (carat, abbreviation ct) and the purity grading of gold alloys (karat, abbreviation kt).

The carat (ct)

The weight of gemstones (including diamonds) is expressed in carats (1 carat = 0.2 grams). One carat is divided into 100 points. In practice, the weight of a diamond is indicated to two decimal points, e.g. 1.35 ct (which represents an accuracy to 0.002 grams). The weight of a 1.35 ct diamond can be, therefore, expressed as "one carat thirty-five". A weight of 0.35 ct can be expressed as "thirty-five points".

The word "carat" comes from the Greek "kerátion" or from the Arabic "kharrūb", which are both names for the seed pods of the Carob tree. In the past, the gemstone traders noticed that the seeds of the Carob tree have an almost constant weight of 0.197 grams. They adopted this weight as the standard unit of a gemstone weight. In the year 1907, the metric carat, representing one fifth of a gram, was recognized as a standardized unit of weight of a gemstone.

The value of a diamond cannot be simply calculated as a multiple of the carat price and the carat weight. A 1.20 ct stone is much more rare than a 0.30 ct stone. Therefore, the price per carat of a 1.20 ct stone will be much higher than the price per carat of a 0.30 ct stone. In fact, there are several carat weight boundaries after which there is a sudden leap in the carat price of a diamond.

The karat (kt)

The word karat represents the ratio of pure gold / other metals in a gold alloy. It is expressed in karats (or thousands). Pure gold is 24 karat or 1000/1000, 18 karat gold is divided 750/1000 or 3/4 pure gold and 1/4 other metals.

Gold alloys
24 karat1000/1000	22 karat916/1000	20 karat833/1000	18 karat750/1000	14 karat585/1000	9 karat375/1000	8 karat333/1000

 

3. PRECIOUS AND SEMI PRECIOUS STONES

What Is A Precious Stone?

What is the difference between precious stones and semi precious stones? These terms are based on old traditions from the west. These days, all gemstones are considered precious since they are all rare and there is a limited supply of them.

The traditional list of gemstones that are considered precious stones are Diamond, Ruby, Emerald and Sapphire. All other gemstones are considered as being semi precious stones. However, these are old terms and not necessarily true these days.

 

• DIAMOND

Possessing the highest shine of all transparent gemstones, diamond is the hardest material on earth that can only be scratched with another diamond. Its name comes from the ancient Greek adámas meaning “unbreakable”.

Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths of 150 to 250 kilometers (93 to 155 mi) in the Earth's mantle, although a few have come from as deep as 800 kilometers (500 mi).
 

Understanding the 4 C’s

In order to determine their quality, diamonds are graded using the 4 C’s system: color, cut, clarity and carat weight.

 

• RUBY

A variety of the corundum family, ruby is famous for its deep red hue and vibrant glow. Ruby is the red variety of the mineral corundum, one of the hardest minerals on Earth, of which the sapphire is also a variety. Corundum is the mineral form of alumina which crystallizes in the hexagonal system. The red color of ruby results from a small admixture of chromic oxide. Only red corundum is entitled to be called ruby, all other colors being classified as sapphires. The most prized tint is blood red or crimson known in the trade as 'pigeon's blood' red. 
 

Over the years, finest-quality rubies have broken auction price records, commanding the highest per-carat value of all colored gems.

 

!Watch for the Silk!

Pure rubies exhibit thin inclusions called needles. When they intersect in groups, they create a phenomenon called “silk” which softens the color causing the light to beautifully scatter across the stone’s facets.

 

• EMERALD

Emerald is one of the most fascinating and beautiful gemstones. Emerald is a precious gemstone and a variety of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. The crystals are usually small with average length of 2 - 5 cm and width of 1 - 1.5 cm. Larger crystals are usually semitransparent to opaque. 

 

The most desirable color is a slightly bluish green in a medium dark tone with strong to vivid saturation. Clarity is important, but inclusions are tolerated more in this variety than virtually any other gem. Top quality, unenhanced stones (with certification) can bring as much as 50% more in price than treated stones of the same size, color, and clarity.

The rich green stone has been a gem of fascination for royalty in the past centuries. Cleopatra, the famous Queen of Egypt, loved wearing them.

 

The Perfect Cut

The precious stone often has intricate inclusions called “jardin” (the French term for garden) which make cutting the gemstone more challenging. Gem cutters have hence developed a special cut called emerald cut which gives the stone a rectangular or square shape.

 

• SAPPHIRE

Pure sapphires are actually white, but in the presence of titanium and iron traces they acquire a velvety blue colour. Apart from this classic shade, there are the less available “fancy sapphires” that come in every colour from green to pink and even black, except for red sapphire which is the ruby.

Sapphire is the most precious blue gemstone. It is a most desirable gem due to its color, hardness, durability, and luster. Value of this gemstone depends on its size, color and transparency. Top-quality sapphires are extremely rare in all the gemstone mines of the world. Cutting of this gemstone requires great skills and experience and it is the job of the cutter to orientate the raw crystals in such a way that the color is brought out to its best improvement.
 

The world’s most famous sapphire engagement ring is the one previously owned by the late Diana, Princess of Wales, and currently worn by Catherine, Duchess of Cambridge.

 

See the GIA link on the description of gemstones at: https://www.gia.edu/gem-encyclopedia