The diamond industry uses very specific grading standards to set a diamond's value. Grading standards reflect "very subtle" gradations of differences---a small carbon spot, slight shift in colour, or small imperfection in the cut or polish of the diamond will significantly affect its value. Once a stone gets above VS in clarity it generally appears to the unaided eye to be "perfect". 

The following are the most widely accepted clarity grading terms and their descriptions:

FL-IF: Flawless, Internally Flawless

(Inclusions are too small to be illustrated)

No inclusions visible under 10X.   The highest clarity grade given. Some blemishes may be permitted externally thus bringing the stone to a clarity of "IF" or Internally Flawless.

VVS1-VVS2: Very, Very Slight Inclusions

(Inclusions are too small to be illustrated)

Extremely difficult to find under 10X magnification.

VS1-VS2: Very Slight Inclusions

Difficult to find under 10X magnification.

SI1-SI2-SI3: Slight Inclusions

SI1 - Can be seen easily with 10X magnification. Cannot be viewed with naked eye. 

SI2 - Can be seen easily with 10X magnification. Rarely can be viewed with naked eye. 

SI3 - Can be seen very easily with 10X magnification. In most cases (stones above ¾ of a carat) can be viewed with naked eye. The majority of diamonds fall into this category.  SI3 - is a relatively new grade added by some laboratories to bridge the very wide gap between SI2 and I1 (imperfect).                          

I1-I2-I3: Imperfect

The Imperfect group is the final group on the diamond scale. Flaws in diamonds in this category are visible with the naked eye. 

I1 - diamonds in the I1 range are still pleasing to the eye. The imperfection is not large enough to take away from the general brilliance of the stone.

I2 - diamonds in the I2 range have large imperfections that in some cases may take up a substantial portion of the stone and can be viewed with ease by the naked eye.

I3 - diamonds in this range are very close to be considered “rejection grade” stones.  This means that such a large part of the stone is included that the stone has lost all “life” and has no appeal left it. Any stone lower than I3 would be considered an industrial grade stone.

The size and number of imperfections determine the clarity grade:

Comparative size of imperfections and subsequent grades

Comparative number of imperfections and subsequent grades

The Second “C” - CARAT WEIGHT

A diamond's weight is the simplest characteristic to measure, and from the earliest times has been used to appraise the value of a diamond. The metric carat (abbreviated ct., which equals 0.200 grams or about 7/1000 ounce avoirdupois) is the international standard unit of weight for diamonds and most other gems.  The carat measurement indicates the true mass and weight of a diamond.  Diamond weight is also commonly expressed in "points," 100 points being equal to one carat.  Fifty points is equal to 1/2 carat.

Note: Do not confuse carat with karat. Carat refers to stone weight while karat refers to fineness of gold weight.

It is very important not to mistake carat weight as referring to the dimensions of a diamond.  It refers to weight only. Why the distinction? Because weight can hide in different parts of the stone.  You can have a) well-cut, b) deep, or c) shallow diamonds.  Some may appear larger than others due to its cut.  It is, accordingly, important to understand that there is no direct relationship between perceived size and weight: a fifty point diamond is NOT twice as large to the eye (or as wide) as a twenty five point diamond.  It is only twice as heavy and only somewhat larger looking.

Carat weight evolved from early merchant traders who used wheat grains and then carob seeds as standards of measurement for gemstones. The word carat comes from the Greek “keration” which referred to the seeds of the carob tree.  These seeds are small and relatively uniform in weight.  I’ve tried this and can report that the seed from pod of the carob or locust tree remarkably weighs about one carat. Not until 1914 was the standard metric carat adopted in Europe and America.  

The size of a diamond has the biggest impact on price.  All other factors being equal, the larger the diamond the greater its cost.  Diamonds lose approximately 40-60% of their rough weight when they are cut.  Over 1 million rough diamonds must be mined before one is found that can be cut into a 1.00 carat finished diamond!

With each weight category increase (quarter, third, half), the value per carat of a diamond will increase significantly and almost geometrically (given all have the same other factors).  A stone which is twice as large as an otherwise identical smaller stone might be three or more times more expensive.  So while you might see a price for a smaller stone at $2,000 per carat, as you price the same cut, colour and clarity in a larger stone you'll see dramatic increases. 

There are standards for reporting a diamond's weight.  FTC guidelines allow a one-half point (1/2) tolerance in the stated weight of a diamond. For example, a diamond weighing .495 carat can be legally sold as a 50 point diamond, while a .494 carat diamond must be sold as a 49 point stone.  Some stores sell diamonds according to size ranges.

Jewelers may also set weight tolerance for diamond rings and jewelry.  These tolerances often appear in the fine print of ads, catalogs, and flyers. They read "all weights are approximate" or "all weights are accurate to within 5%".  If you advertise or sell jewelry, your product claims must be accurate.  The Federal Trade Commission acts in the interest of all consumers to prevent deceptive and unfair acts or practices.  The Commission's Jewelry Guides explain how to describe jewelry products truthfully and non-deceptively. This brochure addresses marketing claims about diamonds, gemstones and pearls.   You can see a copy by clicking this link: Guides for the Jewelry, Precious Metals, and Pewter Industries.  Sellers need to focus particular attention to make sure that descriptions about these products are not misleading and that important, material information is disclosed to consumers.

Often it is not practical to remove a diamond from its setting to arrive at an accurate weight.    Diamond weight may be estimated by formula: 

DIAMOND CARAT WEIGHT FORMULAS

To find the approximate weight of a diamond, use the appropriate formula below. All measurements are to be made in millimeters (mm).

Please note that although these formulas are normally fairly accurate, the results will only be as accurate as your measurements and will still only be an estimate.  The only sure method for determining the true weight of a diamonds is to weigh it unmounted on a balance or scale designed specifically for that purpose.

CHART of COMPARATIVE DIAMOND SIZES

Note: Use this chart as a relative guide only. (The size will depend on your monitor and may not beaccurate.)

The Third "C" – CUT

The cut or "shape and make" of a diamond can be considered the most important of the "C"’s because the quality of the cut is what gives the diamond its brilliance and beauty and strongly contributes to the diamond’s value. The cut of the diamond is fashioned by human hands and is the only "C" that is not determined in nature.  Diamond cutters cut and polish diamond rough by hand into objects of beauty.  It requires a master cutter to fashion an ideally cut diamond.  Facets are the tiny planes on the diamond's surface, which give it sparkle and fire. The manner in which the facets are angled to each other and the diamond's proportions determine the brilliance (reflection of light from inside the diamond), dispersion (colour refraction-the twinkling of colours) and scintillation (reflection of light from the surfaces of its facets), or more simply, its light refraction, display of spectral colours and their movement, respectively.

In order to maximize this brilliance, the diamond cutter must place each of the diamond's facets, which act as light-dispersing mirrors, in exact geometric relation to one another.  On a classic Round Brilliant cut diamond, fifty-eight facets must be precisely aligned.  Few diamonds are cut to exacting standards since diamond cutters try to maximize their returns on the raw material by leaving the stone as large as possible with minimum waste.  As a result, the proportions, symmetry and perfection of the cut and shape may be delegated to play a secondary role.  The result is usually a compromise between profit (e.g., size) and beauty (perfection of cut, proportions and shape).

When the diamond is well proportioned the path of a beam of light is returned directly back to the eye instead of escaping through the bottom or sides of the cut diamond, as a result the diamond will be more lively and brilliant.

A shallow cut diamond with a large table looks shallow and has poor dispersion not to mention a predisposition to cleavage (breakage).

Well made diamonds have a superior polish with no drag marks, surface waviness or other surface blemishes.

If the diamond is cut too deep and with a thick girdle and small table for added weight you have a dull lifeless stone. 

We will endeavour to give you a basic knowledge of what the best standard in the diamond trade is.  For a diamond to be considered ideal cut all the components (facets, table, crown, pavilion, etc.) must be cut to specific tolerances (angles and percentages).   If not, brilliance and dispersion will suffer.

Marcel Tolkowsky, a family member of Belgian diamond cutters, is credited with calculating in 1919 the ideal proportions and facet angles that create maximum 'balanced' brilliance, scintillation and fire.  Tolkowsky published Diamond Design, the first recorded analysis of round brilliant diamond proportions.  This work was based on theories of light behavior and his opinion of proportions resulted in the best balance of brilliance and dispersion.  These calculations formed the basis or which the American Gem Society (AGS) uses in grading diamonds for proportions.

AGS CUT GRADES

Unfortunately the "ideal cut" results in smaller weight yield from the rough diamond crystal and is rarely practiced.  Most cutters today slightly compromise Tolkowsky's "ideal cut" in what has come to be known as the "American Brilliant Cut" or "Modern American (brilliant) Cut".  The slightly modified cut still creates impressive results.

The most important criteria of the Cut is the ratio of the depth to its diameter (i.e. Depth/Diameter whereby the diameter is that of the girdle's.  In fancy shapes it is the girdle's shortest diameter).  In order for the diamond to be considered within the "Ideal" tolerance bracket the ratio should be between 58/100 and 62.9/100 or, "58%" and "62.9%" respectively.  "Table" diameter percentage (see illustrations for definitions of the names of the different diamond facets), "Crown" angles and "Girdle" thickness & symmetry are also important.  Each of these proportion criteria has its tolerance range which, however, are less crucial when violated than deviations from the above Depth/Diameter ratio ("Percentage"). These tolerance ranges, loosely speaking, are those manifested in the "American Brilliant Cut".  Thus, acceptable table proportion tolerance range for the practical equivalent of the ideal cut ("The Modern American Cut") is larger than the allowed deviation range for its depth: tables are allowed the proportion range of approx. 52% to 62% or 63%.

A well proportioned, finely made (polish) diamond can command a 40 to  50% premium (or more) over an "off make" or a lackluster poorly polished, misproportioned stone (colour, clarity, and weight parameters being the same specs).  Typical cutting & polishing time on a 3/4 carat round brilliant diamond is less than 4 hours.  The same size and shape diamond cut to "ideal cut" (AGS "0" cut) proportions is 3 to 4 days not to mention more loss of rough during cutting.   This difference in labor cost is why very fine cut diamonds command a premium in price. Ideal cuts should have an accompanying AGS certificate.

In fancy cut diamonds (Princess Cut, Emerald, Marquise, Oval, Pear etc.) proportions are measured in relation to the diamond's width—the girdle's cross section narrowest diameter and tend to be considerably larger (in the high 60's and 70's). Remember, however, that if they were close to the ideal cut standards, those proportions would be too low in the longer directions of the diamond (unless the culet was sufficiently stretched as well).

In girdles, even though girdle thickness of “very thick” does not affect a diamond's brilliance it does, however, render the diamond's appearance somewhat smaller as the bulk of its weight is concentrated in the girdle area. Extremely thin girdles, on the other hand, should be avoided due to their fragility in the setting process and after (if exposed).

So, what's the difference between AGS-0, AGS-000, Ideal Cut Diamonds, Tolkowsky, Hearts & Arrows, etc.?  Unless you have special laser optics, not very much.  Side by side all things being equal, i.e. size, colour and clarity you would need a microscope and a well trained eye to tell the difference.  Simply put, these diamonds all reflect back 96 plus percent of the light that enters the stone (AGS-0=96% reflection, Hearts & Arrows=98% where as an AGS-4 (Good) or GIA (N,G,G,N) cut has a reflection rate of 70% or so.  Face up without advanced optical equipment you cannot tell the difference between the ideal cut diamonds.  If the diamonds are mounted you can't tell period.

Ideal cut diamonds are really a hot item now.  Dealers who “romance the stone” insist that this is the only way to go.  I am not trying to put down ideal cut stones.  We appreciate them for their beauty.  We also know that they are in great demand (thanks to all the hype they are getting in the trade).  The big thing now is "ideal cut".  Well, what is all the hullabaloo about?  Basically, ideal cut diamonds are diamonds of a superior make that are cut to display optimum brilliance and dispersion.  Are ideal cut diamonds so superior that customers should not consider purchasing another diamond?   The short answer is a big resounding NO!   Take a trip to the local mall and shop around for a diamond. Whose ideal cut standards are the sales clerks trying to confuse you with?  AGS, EGL, GIA, Hearts and Arrows, European Ideal, Tolkowsky, zero cut, triple zero cut?  There are many differing standards and ranges.  Oh, did someone at the mall forget to tell you that "ideal" is a range?  And you thought "ideal" was specific.  Confused?  Darn those sales clerks!  For our purposes the best standard is what AGS (American Gem Society) uses in grading diamonds for ideal cut proportions.   All others to the back of the line please. 

The Fourth “C” – COLOUR

The colour of a diamond has the second biggest impact on its price, after carat weight.  Did you know that diamonds come in every colour of the rainbow?

Grading colour in the normal range involves deciding how closely a stone's body colour approaches colourlessness.  Most diamonds have at least a trace of yellow or brown body colour.  With the exception of some natural fancy colours, such as blue, pink, purple, or red, the colourless grade is the most valuable.

If a diamond does not have enough colour to be called fancy, then it is graded in a scale of colours ranging from Colourless to Light Yellow, "D" through "Z" or "0" through "10" depending on which lab you use.  A diamond with a "D" colour is considered to be colourless.  If the colour is more intense than "Z", it is considered fancy.  A fancy yellow diamond fetches a higher price than a light yellow diamond.

The gem laboratories only grade diamonds that are unmounted, or "loose", and they do so under special light using colour master sets to compare against.  Once a loose diamond is mounted on a ring, even the trained professional cannot always tell the difference between, say a "D" colour and an "E" or "F" colour diamond.

Cost is sometimes referred to as the fifth “C” and for good reasons.  It is probably the most important factor in your mind.  Let’s take a typical diamond and see what happens when we take it through different colour grades.  We’ll start with a 1.00 carat diamond of K colour and VS1 Clarity.  If you move up to an H colour, you will pay approximately an extra $1,700 US per carat. Move up to F colour, the increase will be approximately yet another $1,000 US per carat.  Improve the colour to D and the increase will be approximately another $900 US per carat.

The high prices commanded by colourless stones result from their extreme rarity rather than from any appreciable effect of body colour on beauty.  To the consumer, the colour grades of diamonds are almost unimaginably subtle; for example, very very slight differences in the colours of two diamonds – undetectable to all but specially trained technicians working under carefully controlled conditions – may result in a price difference of several thousand dollars for the two stones.  Some people see lightly tinted diamonds as warmer and more attractive than colourless stones; using terms like “off colour” or “poor colour” may destroy your admiration of a truly beautiful gem. 

Typically you will see stones with a colour grade D,E,F,G,H,I,J in finer quality jewelry. Colour grades of K,L,M,N are very common in promotional quality jewelry and tend to look dingy in daylight.  When diamonds are graded properly it is done inside in a room with windows facing north only to get natural north lighting. If this is not possible illumination inside the grading rooms are colour corrected to emulate natural north light. The great Diamond Trading Bourses have their trading rooms with windows on the North side of the building - perfect conditions for viewing diamonds. When millions of dollars of diamonds in a single trade are on the line, second-rate lighting just won't cut it.  Grading lamps that diamond graders use also emulate this light. 

Probably the most important reason for colour grade variations between labs and even between different graders in the same lab is simply the narrow size of individual grades.  The differences between colours are literally at the edge of human discernment.  While under optimum conditions graders can generally get within a quarter grade of one another, on lab documents the best reproducibility graders can probably attain is plus or minus one full grade.  Thus today’s F could be either tomorrow’s righteous E or disastrous G. 

Fluorescence 

Some gem-quality diamonds fluoresce: they emit light when exposed to long-wave ultraviolet light.  How does this fact affect a diamond's appearance and value?  In the past, some people in the diamond trade have considered moderate to strong fluorescence as a negative value factor for fine diamonds and a positive value factor for diamonds with a lower body colour.  Why?  The trade perceives diamonds without fluorescence as "more pure" than diamonds with it. There is a perceived rarity for diamonds of fine colour without fluorescence.  Fine quality diamonds with strong fluorescence may be undervalued because rare extremely strongly fluorescent diamonds known as "overblues" have a visible haziness that makes them appear almost cloudy in light with strong ultraviolet content.  Dealers have theorized that strong fluorescence may affect apparent clarity.  At the same time, strongly fluorescent diamonds with a yellowish body colour have long been considered to appear to have a better colour because the blue of the fluorescence makes them appear more white in sunlight, which is a source of ultraviolet light.

Lower-colour diamonds with strong fluorescence sometimes command a premium. The Gemological Institute of America's Gem Trade Laboratory (GIA-GTL), the country's leading diamond grading lab, lists fluorescence as an identifying characteristic, not a grading factor.  Based on a GIA-GTL random sample of data for 26,000 diamonds, diamonds with fluorescence are more rare than non-fluorescent stones: 65 percent of diamonds have no reported fluorescence. Listed below is GIA's list of abbreviations for strength of fluorescence as well as their meanings:

Fluorescent diamonds are nothing new.  In fact, in the old days diamond dealers used the term "blue-white" to refer to colourless (D,E,F) diamonds with strong blue fluorescence.  The term actually became sort of a status symbol amongst the public and to this day people will occasionally ask for a blue-white diamond.  Rule 28 of the Federal Trade Commission's Trade Practice Rules for the Jewelry Industry addresses this issue:

FEDERAL TRADE COMMISSION

Rule 28 Misuse of the term "Blue White"

"It is an unfair trade practice to use the term "blue-white," or any other term, expression, or representation of similar import, as descriptive of any diamond which under normal, north daylight or its equivalent, shows any colour or any trace of any colour other than blue or bluish."

In other words, only a diamond with blue fluorescence can be represented as blue-white.

As you might imagine, fluorescence can be a jeweler's best friend or worst nightmare.  When looking at a diamond, always view the diamond under long wave ultra violet light.  The GIA DiamondLite is equipped with an ultra violet light source as are many other products available to the trade.  If the diamond picks up a light neon blue cast under the ultra violet light, it probably has faint fluorescence that will have little effect on the diamonds appearance or colour grade.  If it displays a strong neon blue colour, it has strong blue fluorescence, which will most likely affect its colour and may cause the diamond to appear oily or foggy.  Once again, the keyword here is "may".

Fluorescence can add to or detract from a diamonds appearance.  The thing to do is determine whether a diamond has it or not, and then decide if it effects the diamonds appearance or brilliance in a way that is acceptable to you.

Compiled by Harold Dambrot of www.pawnbroker.com