Education - Diamond Guide

The color of a gemstone is its most significant characteristic, and many jewelers consider it to be the most vital evaluation criterion. Gemstones are found in all colors. The color of a gemstone depends on following three characteristics: hue, saturation, and tone.

• Hue

Hue is the basic or unique color of the gemstone. Hue is described as the shade, tint or sensation of a color. While almost all gemstones have some shades of other colors, the most valuable gemstones are those that exhibit a pure color and only ‘slight’ hues of other colors in addition to their primary color.



• Saturation

Saturation is a measure of the intensity or purity of a gem's hue or color. A gemstone that is free of gray or brown hues is considered to be strongly saturated and is more valuable than a gemstone with lower saturation. Saturation often decides the cut of a gemstone. A high-quality gemstone cut delivers an even color throughout the stone and exposes the fewest inclusions.



• Tone

Tone represents the depth of a gemstone color, ranging from colorless to black. In other words, tone is described as the relative lightness or darkness of a hue. Gemstone tone is described as ‘light’, ‘medium-light’, ‘medium’, ‘medium-dark’, and ‘dark’. Medium-light to medium-dark tone is considered to be the most valuable range.

All the above three characteristics are associated with each other and play very crucial roles in determining the gemstone’s color. The more intense the color, the greater the value. This does not mean darker, but more intense.

Clarity is a term used to describe the absence or presence of flaws inside or on the surface of a gemstone. A flawless gemstone is rare and usually expensive. Most gemstones have inclusions, or tiny mineral flaws, that can be seen under magnification or by the careful eye. A gemstone may have inclusions, cracks, spots, clouds, or any other blemish or imperfection.

For diamonds, a clarity Grade Scale from F (Flawless) to I3 (Included 3) is used, whereas for other colored gemstones a different grading scale is used. Colored stones are classified into three ‘Types’, which are defined as below:

• Type I


Type I colored stones include stones with very little or no inclusions. This category can include Aquamarine, Blue Topaz, Zircon, Morganite, Tanzanite, etc.

Clarity in the Type I group is classified as VVS (minute to detectable), VS (minor), SI1 (noticeable), SI2 (obvious) or I (included)


• Type II


Type II colored stones include stones that often have a few inclusions. This category can include Corundum, Garnets, Iolite, Peridot, Quartz (Amethyst, Citrine, Ametrine), Ruby, Sapphire, Spinel, etc.

Clarity in the Type II group is classified as VVS (minor), VS (noticeable), SI1 (obvious), SI2 (prominent), or I (prominent, affecting appearance).


• Type III


Type III colored stones includes stones that usually always have inclusions. This category can include Emeralds, Tourmaline, etc.

Clarity in the Type III group is classified as VVS (noticeable), VS (Obvious), SI1 (prominent), SI2 (more prominent), or I1 (affecting appearance or durability).

A good cut is key to giving a gemstone its beauty and brilliance. A gemstone's cut refers to its proportions and symmetry. The stone should be symmetrical in all dimensions so that it will appear balanced, and so that its facets will reflect light evenly, which will provide good brilliance to the stone. A well-cut faceted gemstone reflects light back evenly across its surface area when held face up. If the stone is too deep and narrow, surface area will be dark and if it is too shallow and wide, parts of the stone will be washed out and lifeless.

While cutting, the color of a gemstone should also be considered for optical efficiency. If a stone's color is highly saturated, a shallow cut will allow it to pass more light, while a deeper cut may increase the vividness of a less saturated gem. There is no generally accepted grading system for gemstone cut.

• Cabochon Cut
  
  In the cabochon cut, the upper surface of the stone is smoothed and rounded into a simple curve of any degree of convexity; the lower surface may be concave, convex, or flat. All the remaining cuts have flat facets.
  
  
  
  
  
• Table Cut
  
  In the table cut, the facets of the natural octahedron of the stone are ground to smoothness and polished. One facet, the table, is ground much larger than any other and made the top of the gem, while the opposite facet, the culet, is left quite small.
  
  
  
  
  
• Rose Cut
  
  The rose cut consists of a flat base and (usually) 24 triangular facets—resembling a cabochon with facets.
  
  
  
  
  
  
  
• Brilliant Cut
  
  The brilliant cut is scientifically designed to bring out the maximum brilliancy of the stone. The crown of a brilliant consists of a table and 32 smaller facets, of which 8 are quadrilaterals and 24 are triangles; the base, a culet and 24 larger facets, of which 8 are quadrilaterals and 16 are triangles. The base and crown are separated by a girdle. The brilliant cut has certain proportions—in general, the depth of the crown is one third the depth of the stone and the width of the table one half the width of the stone.
  
  
  
• Other Cuts
  
  

  MazarinCut      OldEuropeanCut     OldMineCut           PointCut             SingleCut

In addition to the above defined cuts, stones are also cut in a variety of square, triangular, step, emerald, and trapezoidal faceted cuts. The use of such cuts is largely determined by the original shape of the stone. Large rubies, sapphires, and emeralds are often cut square or rectangular with a large table facet surrounded by a relatively small number of supplementary facets.

The process of cutting and polishing gems is called gem cutting or lapidary, while a person who cuts and polishes gems is called a gem cutter or a lapidary (sometimes lapidarist). Few gemstones such as pearls and coral (usually referred to organic minerals) are not cut at all and many times left in their natural state. However, it is customary to polish these items, as with all gemstones. The quality of a gemstone's cut can have a dramatic impact on how it looks but only a small impact on the price per carat.


Size

Similar to diamonds, a gemstone’s weight is also measured in carats where one carat equals 200 milligrams. However, in case of gemstones, this may not give an accurate idea of its size, because different types of stones have different densities Two gemstones of the same carat weight may be different in sizes. For example, a 1 carat Sapphire or Ruby will be smaller than a 1 carat Emerald, though they have the same carat weight, because Sapphires and Rubies are denser than Emeralds. At the same time, a 1 carat Diamond will be larger than a 1 carat Ruby as a Diamond is less dense than a Ruby. Gemstones can also be measured in dimensions (diameter, length, and width).


Illustration of gemstone dimensions (L/W = Length to Width Ratio)

Asscher


Baguette


Cushion


Emerald


Heart


Marquise


Oval


Pear


Princess


Radiant


Round


Trillion


In the case of gemstones, larger stones are not always more valuable. The rarity of a certain size will determine the value of a gemstone. A gem that is available naturally in weights of 10 carats or more may be less valuable than one that is rarely available in large sizes.