There are four factors commonly known as the "4 Cs

[fastwalker]

Source: IQ..Full Member:
newcmkx.proboards33.com/index.cgi?board=DD&action=post&thread=1093445226&start=0


www.manchester.com/news/story/1080.html

Also once we all become wealthy here is how the quality of a diamond is determined.
There are four factors commonly known as the "4 Cs" -- Carat weight, Clarity, Color, and Cut.


Carat weight
1 carat is exactly 200 milligrams. Since most diamonds sold in the jewelry industry weigh less than 1 carat, the carat is usually subdivided into "points." There are 100 points in 1 carat, so that a diamond weighing 3/4 carat would be a "75 point diamond." In summary: 1 carat = 200 milligrams = 100 points
The weight of a stone and its size have nothing in common. Also the carats of a diamond are not the same as the carats of a different stone, because different minerals have different densities and thus different weight. It’s all about the weight. You can simply ask the jeweler to weigh the stone in your presence, and take the number of milligrams reported by the instrument, and divide by 200 to get the carat weight of the stone.
Clarity
It is a measure of the number and extent of the flaws in the diamond. Generally speaking, the fewer the flaws, the more valuable the diamond. Completely flawless diamonds are extremely rare -- only a few hundred "FL" diamonds are produced per year worldwide.
FL IF VvS1 VvS2 VS1 VS2 SI1 SI2 I1 I2 I3
FL: Completely flawless
IF: Internally flawless; only external flaws are present, which can be removed by further polishing the stone
VVS1 - VVS2: Only an expert can detect flaws with a 10X microscope. By definition, if an expert can see a flaw from the top of the diamond, it is a VVS2. Otherwise, if an expert can only detect flaws when viewing the bottom of the stone, then it is a VVS1
VS1 - VS2: You can see flaws with a 10X microscope, but it takes a long time (more than about 10 seconds)
SI1 - SI2: You can see flaws with a 10X microscope
I1 - I3: You can see flaws with the naked eye. Consider avoiding I2-I3 diamonds.
There are many different types of flaws. The best way to become acquainted with them is to look at lots of diamonds. The more common ones are as follows:
Pinpoint: A very small white dot on the surface of the stone. The most common flaw.
Carbons: A very small black dot on the surface of the stone. Less common than pinpoints
Feathers: Small cracks within the stone, similar in look to broken glass. Small internal feathers are harmless (other than lowering the clarity rating of the diamond), but large feathers can become a problem because the crack can grow as the diamond ages
Clouds: Hazy areas within the diamond, actually made up of many small crystals that are impossible to see individually
Crystal Growth: A small crystalline growth within the diamond. Looks like a small diamond within the big diamond
Avoid any "clarity-enhanced" diamond is an artificial process used to "fix" the flaws on an otherwise good stone. Although a clarity-enhanced diamond can look nearly flawless (in some cases, it is impossible to detect the enhancement), it is intrinsically worth as much as a flawed stone. It is a good idea to double-check this fact on the G.I.A. certificate. You may want to consider purchasing a diamond with clarity greater than SI1 since it is the least important feature unless you will be pulling out a microscope.

Color

It refers to its degree of "yellowness." The ideal diamond is completely colorless, and therefore it will be the most expensive.

D E F G H I J K L M N O P Q R S T U V W X Y Z
Colorless Near clear Increasing yellow yellow
D = entirely colorless to Z = yellow

The average color for engagement diamonds in the United States is G to H. Jewelers have two tools at their disposal to judge the color of a given diamond. The first is what's known as a "reference set" of stones. A jeweler will compare the stone in question with a set of stones of known color (the set is typically made of cubic zirconium!), and make a qualitative determination as to the color grading of the stone in question. The second, more precise method, is to use a colorimeter, which is nothing more than an electrical device that will measure the optical characteristics of the stone and report the color to within 1/3 of a grade. Most jewelers routinely round the color test results upwards. Therefore, a stone that is only slightly better than an F grade automatically becomes an E and thus becomes more expensive for us to purchase. It is important to see the diamond unmounted. Ask to see a printout from the colorimeter, or ask the jeweler for a reference set of stones to make the comparisons yourself. To do this, place the diamond in question next to the reference stones face down on a white piece of paper, and compare the color of the stones until you get the best match. If the diamond will be put on platinum/white gold D to G range is fine, otherwise on yellow gold J or worse should not make too much difference.

Cut

Refers to the cutting style, the shape of the stone (round, square), its proportions, or the workmanship of the actual diamond-cutting process. It is the most important of the 4c’s.

[fastwalker]

Cutting style
Diamonds, as crafted by nature, and consist of translucent crystalline carbon. If the outer rough could be peeled away, the resulting stone would be as smooth as glass; unfortunately, it would be no more aesthetically pleasing than a piece of glass crystal. The art of the diamond-cutter is to transform that chunk of crystallized carbon into a beautiful piece of jewelry.
Step cut has parallel facets that usually span the length or width of the stone, the "steps" lead from the outer edges to the top of the diamond. If a step-cut diamond has rounded-off facets in the corners, this is a variant of the step-cut called the emerald cut. (Simply looks like a rectangle with steps.)
Brilliant cut has triangular facets that surround the stone and usually culminate on a flat top called a table. The shiniest diamonds have the brilliant cut. (Simply circular with the same engineering like a bridge.)
Shape
It is the intrinsic shape of the diamond. As viewed from the top, the most common shapes are: Oval, Pear, Round, Marquise, Hearth Emerald, Princess, Radiant. Round brilliant diamonds are the most expensive, while the square cuts typically cost about 10% less.
Proportions
All of the light entering the diamond from the top will bounce within the diamond and be reflected back through the top, giving the stone maximum brilliance and fire. If the stone is too shallow or too deep, some light will escape through the bottom part of the diamond, giving the appearance of shadows when viewed from the top. A diamond rich in carat weight but poorly proportioned can be deeply "discounted," giving you a false impression of a great deal.

There are five common metrics used to evaluate the proportions of a diamond. How they are calculated and what they mean:
Depth percentage “c ÷ a × 100 (%)” - This is the most important metric for maximum brilliance. Diamonds that have too small or too large depth percentages will be too deep or too shallow, and will have shadows when observed from the top.
Length/Width Ratio “(a' ÷ a) : 1” - a' is the longest side, and a is the shortest. For round and square stones, the length/width ratio should be close to 1. Other shapes have specific ratios that are most desirable.
Girdle thickness “look at f” - Numbers are not used to measure the girdle thickness -- the girdle is judged from extremely thin to extremely thick. Thin girdles tend to chip; thick girdles "hide" extra, unnecessary weight. An even, medium girdle is ideal.
Pavilion depth percentage “e ÷ a × 100 (%)” - If significantly greater than the ideal, the diamond will have a dark center. If significantly less, the stone will look watery and lifeless.
Crown height percentage “d ÷ a × 100 (%)” - Deviation from the ideal will cause reduced brilliance and fire.
Table percentage “b ÷ a × 100 (%)” - The bigger the table percentage, the greater the brilliance and the lesser the fire, and vice versa. The ideal table percentage strikes a perfect balance.

An "ideal cut," according to Tolkowsky, has the following characteristics:
· Round in shape, and brilliant-cut (58 facets)
· Depth percentage: 59%
· Table percentage: 53%
· Crown height percentage: 16%
· Pavilion depth percentage: 43%
· Girdle thickness: Medium and even all the way around the diamond
· Symmetry: Perfect
· Perfectly aligned and formed facets
· Very small or absent culet
Proportions and Non-Round Shapes
When you decide to purchase a diamond that is not round, you have an inherently asymmetrical diamond, and therefore you sacrifice brilliance and fire.
"Cut" is the least understood and perhaps the most important of the 4 Cs. An inferior cut will yield a lifeless, dull diamond.

Round
Excellent Very Good Good Fair / Poor
Depth % 58.5-62.8% 55.0-58.5% or 62.8-64.0% 53.0-55.0% or 64.0-67.0% Outside of these ranges
Table % 53.2-61.2% 51.1-53.2% or 61.2-64.5% 49.0-51.1% or 64.5-68.0% Outside of these ranges
Length/Width Ratio 1.05:1.00 1.10:1.00 1.15:1.00 Outside of these ranges



General Workmanship
diamond's value and intrinsic beauty are governed by additional aspects of the workmanship of the diamond cutter. A round diamond has exactly 58 facets -- 33 above the girdle, and 25 below. The Girdle is nothing more than the equator is on Earth for comparison purposes. It is the middle part, of the diamond, and is measured from "extremely thin" to "extremely thick". Thin girdles are prone to chipping. Extremely thick girdles hide a lot of weight, so you end up paying for a heavier diamond that doesn't look that big. The ideal is an even, medium girdle; this applies to all shapes EXCEPT for the tip of the pear shape, in which a thick girdle is preferred to make it less prone to damage. When examining the girdle, make sure that it is well-faceted and polished, since some diamond cutters will omit this step to save time and to avoid removing weight from the stone. Also make sure the diamond is completely symmetrical in every way.