Know your Diamond:

 Diamonds being so valuable, it was essential to have a universal grading system for comparing their quality. In the 1940s and ’50s, Gemological Institute of America (GIA) developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds. Today the GIA Diamond Grading Report and the GIA Diamond Dossier® are considered to be the world's premier credentials of diamond quality.

• GIA 4Cs Colour
• GIA 4Cs Clarity
• GIA 4Cs Cut
• GIA 4Cs Carat Weight

GIA 4CS COLOUR

Diamond colour is all about what you can’t see. Diamonds are valued by how closely they approach colourlessness – the less the colour, the higher their value. (The exception to this is fancy colour diamonds, such as pinks and blues, which lie outside this colour range.) Most diamonds found in jewellery stores run from colourless to near-colourless, with slight hints of yellow or brown.

GIA’s color-grading scale for diamonds is the industry standard. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or light yellow or brown. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price.

GIA 4CS CUT

Cut quality is the factor that fuels a diamond’s fire, sparkle and brilliance. The allure and beauty of a particular diamond depends more on cut quality than anything else.

The GIA Diamond Cut Grading System for standard round brilliants in the D-to-Z color range is based on the assessment of seven components. The first three — brightness (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the pattern of light and dark areas and the flashes of light, or sparkle, when a diamond is moved) — are appearance-based aspects. The remaining four — weight ratio, durability, polish, and symmetry — are related to a diamond's design and craftsmanship. 
 

In GIA’s system, each component is assessed individually, taking into account the relative importance of that component in the overall cut quality of the diamond. Each cut grade, based on a relative scale from Excellent to Poor, represents a range of proportion sets and face-up appearances. There are many different proportion sets that produce attractive diamonds.

For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion that’s known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. It is important to note that a wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light and how attractive the diamond is to the person viewing it.
 

While it is important to consider many components when assessing the overall cut appearance and quality of round brilliant diamonds, an individual's preferences also play a role. Because each cut grade represents a wide range of proportion sets, individuals have the freedom to choose which particular appearance they prefer within the grade range.
 

The diamond industry as well as the public can use cut along with color, clarity, and carat weight to help them make more informed decisions when assessing and purchasing round brilliant diamonds.
 

People often use the words cut and shape interchangeably. They think of cut as the shape or outline of the diamond, rather than the arrangement of facets needed to create an attractive face-up appearance.

Round is the shape used in most diamond jewelry. All other outlines are known as fancy shapes. Examples of traditional fancy shapes include the marquise, pear and oval. Hearts, triangles and a variety of others are also gaining popularity in diamond jewelry.

GIA 4CS CLARITY

Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes).

Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond’s value. Using the GIA International Diamond Grading System™, diamonds are assigned a clarity grade that ranges from flawless (FL) to diamonds with obvious  inclusions (I₃).

Every diamond is unique. None is absolutely perfect under 10× magnification, though some come close. Known as Flawless diamonds, these are exceptionally rare. Most jewelers have never even seen one.

The GIA Clarity Scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.

• Flawless (FL)- No inclusions or blemishes are visible to a skilled grader using 10× magnification
• Internally Flawless (IF)- No inclusions and only blemishes are visible to a skilled grader using 10× magnification
• Very, Very Slightly Included (VVS₁ and  VVS₂) - Inclusions are difficult for a skilled grader to see under 10× magnification
• Very Slightly Included (VS₁ and VS₂) - Inclusions are minor and range from difficult to somewhat easy for a skilled grader to see under 10x magnification
• Slightly Included (SI₁ and SI₂) - Inclusions are noticeable to a skilled grader under 10x magnification
• Included (I₁, I₂, and I₃)- Inclusions are obvious under 10× magnification and may affect transparency and brilliance

GIA 4CS CARAT WEIGHT

Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewellery weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat.  Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)

Source: GIA

A gemstone (also called a gem, fine gem, jewel, precious stone or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli) or organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond worker is a diamantaire. GIA Gemological reports identify whether a coloured stone is natural or synthetic, and provide a full assessment of the stone’s characteristics, and may also include country of origin determination for certain gem material. Issued for any loose or mounted, rough or polished material, the reports also disclose any treatments detected during analysis.

 

Gemstones by colour

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ALEXANDRITE		OPAL
AMBER		PEARL
AMETHYST		PERIDOT
AMETRINE		ROSE QUARTZ
AQUAMARINE		RUBY
CITRINE		SAPPHIRE
EMERALD		SPINEL
GARNET		SUNSTONE
IOLITE		TANZANITE
JADE		TOPAZ
KUNZITE		TOURMALINE
LAPIS LAZULI		TURQUOISE
MOONSTONE		ZIRCON
MORGANITE