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DeGwyn Gems, Private Jewelers since 1975

Diamond

The crystallized form of Carbon, Diamond can be found in all colors although the colorless variety is the most recognized.

DeGwyn Gems, Private Jewelers since 1975
 

History

Classification and Grading

Characteristics of Diamond

Evaluation

Treatments and Enhancements

Buying a Diamond, Things to Consider

Bibliography


History

Diamonds have been highly prized and valued as a gemstone since early times and can be found mentioned in the writings of all early civilizations. Diamonds' beauty and durability have always been highly regarded and they were used in many statues to early gods and goddesses.

Some of the most famous and noteworthy Diamonds can be found in the crown jewels of many nations. The largest cut Diamond, for example, is the Cullinan I, a 530 ct. oval stone can be found in the British Royal Sceptor. Other historically significant stones include the Black Orloff, a 67.50 ct. Black Diamond, the Eisenhower, a 3.11 ct. stone found in Arkansas' "Crater of Diamonds" State Park and perhaps the most famous Diamond, the Hope, a 44.50 ct. Blue Diamond currently on display at the Smithsonian Institute, Washington DC.

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Classification and Grading

Diamond can be defined as opaque, translucent or transparent crystallized Carbon ranging from colorless to deeply hued. It can be found in all colors but is most often seen in commercial jewelry as colorless with varying shades of yellow.

Because the value of Diamond is closely linked to its perceived quality a complete system of classification and grading has evolved. The standard used in the Diamond trade for the evaluation of Diamond has been developed by the leading authority on Diamonds and Gemstones, the Gemmological Institute of America.

Please see the section entitled, "Buying a Diamond, Things to Consider" for a discussion of this evaluation and grading system.

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Characteristics of Diamond

  • Chemical Composition - Carbon, C.
  • Crystallography - Cubic System.
  • Hardness - 10 on the Moh's Hardness Table
  • Cleavage - Strong
  • Fracture - Conchoidal, brittle
  • Characteristic inclusions - material other than Diamond encased within the stone, cracks, chips, crystal growth lines, and twinning are often seen.
  • Fluorescence - Weak to strong blue, alternately yellow and green

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Evaluation

Diamond of high quality is characterized by the absence of all color with no overtones or undertones of yellow. Although imperfections are common in Diamond, high quality is characterized by no imperfections visible under 10X magnification. This absence of color and lack of visible imperfections is enhanced by the method of cutting and attention to the overall proportions of the finished stone to exhibit the greatest return of light, known as brilliance and scintillation. The final finish should be blemish free and the facet symmetry and placement should be flawless.

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Treatments and Enhancements

The most common treatments and enhancements of Diamond:

  • Irradiation - Using Radium salts, this older form of irradiation resulted in green stones with detectable residual radiation. Today the use of cyclotron and electron bombardment has eliminated the radiation problem and results in green coloration. Using other elemental bombardment results in blue coloration These treatments tend to be characterized by shallow penetration of the coloration.
  • Coatings have long been used to enhance or improve the color of Diamonds. Most such treatments are not permanent and stones treated in this manner should be avoided.
  • Laser - With the advance of laser technology, imperfections in Diamonds, especially dark imperfections, can be modified by laser drilling to the imperfection and treating the imperfection with bleaching or dying agents.

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Buying a Diamond, Things to Consider

Buying a Diamond is a matter of balancing the four components that determine the quality of a Diamond. These characteristics, known as the four C’s, Carat, Clarity, Color and Cut are a universal standard of the Gemological Institute of America (GIA) and are considered as the recognized standard worldwide when discussing Diamond quality.

Size

First, and most obvious, is size. Diamonds' and precious gemstones' weights are measured in carats.  A carat is defined as 200 milligrams or 1/5 of a gram which is approximately 1/5th the weight of a standard paper clip. As a decimal measurement, a one carat stone is 1.00 ct., a half carat is 0.50 ct., etc. Generally speaking, the larger the Diamond, the more valuable it is.

Because of the subjective nature of Diamond buying, certain sizes of Diamonds have a greater demand than other sizes. At one time, these favored stones were subject to a premium value. This “surcharge” was based entirely on the fact that a given Diamond weighed a specific weight. The 1.00 ct. Diamond carried such a premium, as did the 0.50 ct. Diamond.

Although these premiums are no longer common, these exact sizes do correspond to particular size categories in the pricing structure of Diamond. Diamond pricing is usually discussed as price per carat for a stone. At the one carat level, a 1.00 ct. Diamond is more expensive per carat than a 0.99 ct. stone simply because it crosses the one carat price boundary.

Considering the fact that the human eye cannot see this small difference is size, it makes sense to take advantage of this pricing category and select the smaller stone at the lower price per carat.

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Clarity

The next element to consider when buying a Diamond is Clarity. Clarity is defined as the level of imperfection when viewed under 10X magnification. Although many retail establishments now show Diamonds under up to 40X magnification, the industry standard for examination of a Diamond is 10X magnification with color correction. This standard comes from the fact that once you identify an imperfection under 10X magnification, you should be able to resolve that imperfection with the naked eye. A Diamond that has a Clarity grading of Internally Flawless would undoubtedly show imperfections if examined under a higher magnification.

Imperfections are made up of two general types, inclusions and flaws. Inclusions are usually either white or black in color and can be small pinpoints or large collections of included material within the body of the Diamond. It was once thought that the black inclusions were carbon that had not crystallized. We now know that most included material is, in fact, non-Diamond in nature and may be other minerals that were trapped during the Diamond’s crystallization process.

The second type of imperfection common in Diamonds is made up of two related categories of flaws, the feather and the cleavage. Both of these terms describe types of cracks. When a crack is entirely contained by the body of the Diamond and does not touch any surface, it is termed a feather. When a crack does break the surface of the Diamond, it is termed a cleavage.  Again, these types of imperfections can be either small or large and although one should generally avoid seriously cracked Diamonds, a Diamond with a totally enclosed feather is decidedly preferable to a Diamond with a cleavage crack. The reasoning behind this is that the feather, which most likely occurred during the crystallization of the Diamond, is unlikely to grow or weaken the overall integrity of the Diamond. The cleavage crack, on the other hand, certainly has the potential of becoming larger and may eventually weaken the stone resulting in fracture or separation. The term cleavage itself refers to the nature of the crystal structure of Diamond, essentially plates of closely packed carbon atoms. These plates or planes of atoms are extremely difficult to cut through (the reason Diamond is the hardest natural substance on the planet) but extremely easy to separate. When a cleavage crack is within a few degrees of one of these planes, the likelihood of separation and fracture damage resulting from an impact increases greatly.

GIA Diamond Clarity grades are represented as follows:

IF - VVS1 - VVS2 - VS1 - VS2 - SI1 - SI2 - I1 - I2 - I3

IF - Internally Flawless – A trained Gemologist, after careful examination, should be unable to distinguish any imperfections under a corrected 10X magnification. Stones with minor surface imperfections but otherwise internally flawless are not penalized since these imperfections can usually be corrected with re-polishing.

VVS - Very, Very Slightly Imperfect – A trained Gemologist after careful examination should be able to distinguish imperfection under 10X magnification but even if pointed out by the Gemologist, the layperson would have extreme difficulty seeing the imperfection.

VS – Very Slightly Imperfect – A trained Gemologist after careful examination should have no difficulty distinguishing imperfections under 10X magnification and once pointed out, the layperson should be able to see the imperfection.

SI – Slightly Imperfect – Imperfections are easily distinguished under 10X magnification both by a trained Gemologist and a layperson.

I – Imperfect – Imperfections are distinguishable without any magnification.

With regard to value based on Clarity, the fewer the imperfections visible under 10X magnification, the more valuable the Diamond is.

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Color

The next element to consider is Color or, more accurately, the absence of color. Although Diamonds can be found in almost every color, nearly 90% of the Diamonds mined have, to some degree, a yellow body color. Diamonds with colors other than yellow or colorless are usually individually priced based on the intensity of the color they display with red Diamonds currently commanding the highest per carat price.

The human eye is capable of discerning millions of hues and color variations and Diamond color evaluation can only be done by comparison to other Diamonds, i.e., one Diamond is more or less yellow than another. It is the absence of this yellow body coloration that is desirable and therefore more valuable.

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 Colorless | Faint Yellow | Light Yellow | Yellow | Yellow to Fancy

GIA Color grading uses letter grades to describe the degree of yellow body color. The grading system starts with the letter “D” to represent a Diamond with no body color whatsoever. Each subsequent color grade denotes a slightly greater degree of yellow visible in the Diamond. It is sometimes confusing to understand these grading system since the “colorless” range of grades includes D, E, and F. How, you ask, can you have three grades of colorless? The easiest way to understand this is using the following analogy. If there were three glasses of water in front of you and one was described as ‘clear,’ the next was described as ‘water clear,’ and the third was described as ‘crystal clear,’ you would easily distinguish between the three glasses. The same is true of D, E, and F color Diamonds. There are subtle differences in these three grades that, with direct comparison, are evident. Stones classified as G and H have a very slight yellow tint. Smaller stones of these grades, once mounted, appear nearly colorless. I, J and K color stones have a noticeable yellow tint and are sometimes described as ‘steely’ in color. Diamonds with distinct yellow body color are graded in the L, M, and N grades. Stones that are dark yellow or brown are O, P and Q grades.

Diamonds that have a certain pleasing, crisp and clean yellow color fall under a specific category known as Canary and are priced according to the intensity and beauty of their yellow body color. They should not be confused with dark or dingy yellow stones.

The GIA color grades begin with D and not A, B, C because, although the colorless Diamond is more valuable than the Diamond of noticeable yellow body color, it should not be implied that any color is more desirable than another, especially if a jewelry design that utilizes Diamond is enhanced by using distinct yellow body colored stones.

However, with regards to value based on color, the closer a Diamond comes to being colorless, D in color grade, the more valuable it is.

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Cut or Proportion

The last consideration in buying a Diamond is the way in which the stone is fashioned. There are a number of elements to understand in this regard. First is the overall shape of the Diamond. There are round shapes, square cornered Emerald and cushion cut shapes, boat shaped marquis and myriad variations on these standard shapes. There are also specialty cuts that have become more available in recent years. Examples of these specialty cuts include the Princess cut, the Radiant cut and the Trillium cut.

The modern round Brilliant Cut of Diamond has the following facets as shown in Figure 1: The topmost or Table facet, the circumference of the stone or Girdle facet, the thirty-three facets above the Girdle are the Crown facets, the twenty-five facets below the Girdle are the Pavilion facets and the facet at the very bottom or point of the Pavilion is the Culet.

Standard facets of the modern round Brilliant Diamond

Figure 1

Regardless of the shape, the ultimate purpose of cutting a rough Diamond is to take advantage of the physical properties of Diamond and its ability to transmit and reflect light and ultimately return that light to the viewer.

Light behavior in a well proportioned Diamond

Figure 2

In a properly proportioned stone, a light beam (indicated in Figure 2 above by the dotted line) enters the stone and is refracted or bent as it enters the denser medium (Diamond.) It continues to travel inside the stone and because of the angle of the Pavilion, it is reflected within the stone and finally exits the top of the stone where it has been refracted again as it exits to a less dense medium (air.)

To have light that enters a Diamond be refracted and reflected in such a way that all light entering the top of the stone exits the top of the stone, definite fixed proportions are required in the cutting. These proportions indicated here are known as the Ideal Cut. The original proportions, shown in Figure 3, of the so-called Ideal Cut were devised in 1919 by Marcel Tolkowsky, a mathematician, and first presented in his Masters thesis.

The Tolkowsky Ideal Cut proportions

Figure 3

The criteria for Diamond proportions is based on the cross-section of the symmetrical round cut and it is this round cut stone that presents the best return of light of all the Diamond shapes. The Tolkowsky Ideal Cut proportions have been the standard for over eighty years and still represents the most effective cutting criteria for light return.

Recently there has been some effort to apply modern scientific understanding to the light optics and appropriate proportions for cutting Diamonds and there are now a number of alternative "ideal" proportions that claim to enhance the brilliance and scintillation of the finished cut Diamond. Although there is some validity to these claims, most are based on the original  understanding of how light behaves within a Diamond and the original Tolkowsky devised  proportions.

The value of a Diamond increases with how close the proportions of the Diamond come to this "Ideal Cut."

Finally, the final surface finish should be free from scratches, pits or polishing marks. The facets should be symmetrical with the corners of each facet meeting their adjoining facets exactly. There should not be any 'extra facets' which indicate a mistake in cutting. The Girdle can be either faceted or have a frosted appearance but should be no thicker than is necessary for the stone to be securely set in its mounting. Although in some stones there is an absence of the culet entirely, when present, the Culet facet should be no larger than is necessary to avoid chipping.

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Bibliography