What makes a diamond sparkle
Brilliance is an essential attribute of a beautiful diamond and has 2 components; brightness and contrast. Bright diamonds return lots of light from the surroundings back up through the crown to a 'face up' observer. If light from above leaks out the back of a diamond, naturally it has less brightness. But light that enters and leaves in the face up direction is wasted because your head blocks the lights. Diamonds that are too deep or very shallow do this -they have areas that act like a mirror back to the viewer; they return less light and so they have less brightness.
To be brilliant, a diamond needs more than just brightness. Consider the contrast of a chess board, although it has only 1/2 the light return of a sheet of white paper, it appears brighter, especially when it is moved because it 'scintillates'.
Fire or dispersed light appears as flashes of rainbow colors. You see more fire in darker environments like restaurants that have just a few point light sources or just a flickering candle. Fire is also a result of a diamond's symmetry and proportions. There are several factors that greatly influence the amount of fire a diamond produces such as star facet length, lower girdle facet length, pavilion angle, facet junctions, the angle at which light enters the diamond, and the angle of the light rays as they exit the diamond.
Diamond experts have known for a long time that steep crown angles and small tables (like 'old cut' diamonds) produce more fire. But this combination also produces less light return. Less light return makes it easier to see fiery flashes that might otherwise be swamped by bright white sparkles; this is one reason is why old cut diamonds and some fancy cuts appear to have a lot of fire.
Scintillation is the intense sparkles in a diamond as it moves. Black and white sparkles of scintillation show well in flood lit or office lighting environments where fire can be totally absent. Under pin point or spot lights fire also adds to scintillation. Ideally a diamond has many pleasing flashes spread across the surface of the stone, with few dull dead patches.
Polish is graded the same way as symmetry: Ideal, Excellent, Very Good, Good, Fair or Poor on a GIA report. Poorly polished facets may reduce the intensity of light reflected from, or refracted into and out of, a diamond. Labs assess polish by examining the diamond, facet by facet, with reflected light under a microscope; you or I may not see any difference.
HOW SYMMETRY AND PROPORTIONS MAXIMIZE LIGHT RETURN
Every facet in an Ideal Cut diamond must be placed at precise angles and contain precise proportions. This ensures an Ideal balance between maximum brilliance and dispersion of light. Any discrepancy from these proportions will disrupt the even distribution and dispersion of light within the stone, resulting in a loss of sparkle.
Choosing a shape
The most traditional shape is the round brilliant diamond. This is the choice of many and the first image that comes to mind when diamonds and diamond rings come to mind.
Only the masterful skill of the diamond cutter can attempt the transformation that the raw diamond crystal goes through. From raw material to incredible and unique.
ROUND BRILLIANT
This is the shape that has set the traditional standard for all diamond shapes. Over 75% of the diamonds sold today are Round Brilliant. Its 58-facet cut, divided among its crown (top), girdle (widest part) and pavilion (base), is calibrated through a precise formula to achieve the maximum in fire and brilliance.
FANCY CUT DIAMONDS
Oval — This is a symmetrical design which is even and appeals to many small handed women seemingly elongating hands and fingers.
Marquise — This shape is elongated with pointed ends. The smile of the Marquise de Pompadour inspired this shape which was then commissioned by the Sun King, France's Louis XIV, who wanted a diamond to match it. It is beautiful as a solitaire or when matched with smaller complimentary diamonds.
Pear — This cut combines the oval and marquise shapes. It is the hybrid shape that looks like a sparkling teardrop. It beautifully compliments the average size hand and fingers. It is gorgeous for pendants and earrings.
Heart — A pear shaped diamond with a cleft on the top. The extraordinary skill of the cutter determines the beauty of this cut. Look for a stone with an even shape and a well-defined outline.
Emerald — This shape is known as a step cut because its concentric broad, flat planes resemble stair steps. A rectangular shape with cut corners. Inclusions and inferior color can be more pronounced in this particular cut. So clarity and color should be looked at carefully and time taken when a choice is made.
Princess — This is a square or rectangular shape with many facets. This is a relatively new cut and often finds its way into solitaire engagement rings. It is attractive with longer fingers. This cut requires more weight to be directed toward the diamond's depth in order to maximize brilliance. Depth percentages of 70% to 78% are common.
Radiant — This is a square or rectangular shape. The elegance of the emerald and the brilliance of the round shape marks this cut. 70 facets maximize the effect of its color refraction. Depth percentages of 70% to 78% are common.
Cushion Cut — Late 19th and early 20th style antique type shape. Remnants of the "Old Mine Cut", a deep cut with large facets.
Asscher Cut — This cut was made popular in the 1920's by the Asscher Diamond Company in Amsterdam. Its art deco feeling was very popular at the time. The company went out of business during the Depression and Asscher cuts disappeared from the market. Recently this shape has come back into style.
A well-proportioned pavilion is especially important to a diamond's brilliance. Brilliance is the brightness created by the combination of all the white light reflections from the surface and the inside of a polished diamond. If the pavilion is too deep or too shallow, it causes light to strike outside the critical angle - the largest angle at which light rays inside the diamond can escape - causing the light to exit through the pavilion rather than reflecting back to the eye as brilliance.
DIAMOND ANATOMY
Table: The flat facet on the top of the diamond. It is the largest facet on a cut diamond.
Crown: The upper part of the diamond above the girdle. Consists of a large flat area on top called a table, and several facets below it
Girdle: The outer edge or the widest part of the diamond forming a band around the stone.
Pavilion: The bottom part of the Diamond, below the girdle.
Depth: The height of a diamond from the culet to the table. The depth is measured in millimeters.
Crown angle: The angle at which a diamond's bezel facets intersect the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light entering at the different angles in broken up into its spectral hues, creating a beautiful play of color inside the diamond. The crown angle also helps to enhance the brilliance of a diamond.
Table percentage: The value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, a diamond with a 60% table has a table which is 60% as wide as the diamond's outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters (this millimeter measurement does not appear on diamond grading reports) by the average girdle diameter. For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone.
Facet: The smooth, flat faces on the surface of a diamond. They allow light to both enter a diamond and reflect off its surface at different angles, creating the wonderful play of color and light for which diamonds are famous. The table below shows all the facets on a round brilliant cut diamond. A round brilliant has 58 facets (or 57 if there is no culet).
Symmetry: Refers to variations in a diamond's symmetry. The small variations can include misalignment of facets or facets that fail to point correctly to the girdle. Symmetry is regarded as an indicator of the quality of as diamond's cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.
Fluorescence: An effect that is seen in some gem-quality diamonds when they are exposed to long-wave ultraviolet light (such as the lighting frequently seen in night clubs). Under most lighting conditions, this fluorescence is not detectable to the eye. However, if a diamond is naturally fluorescent, it will emit a soft colored glow when held under an ultraviolet lamp or "black light." Fluorescence is not dangerous to the diamond or to the wearer; it is a unique and fascinating quality that occurs naturally in a number of gems and minerals. Most commonly diamonds fluoresce blue, but can also fluoresce yellow or white depending on which trace elements are found in the matrix of the diamond crystal. Fluorescence is described as none (or inert), faint, negligible, medium, strong and very strong.