The function of cut is to display the gemstone's inherent beauty to the greatest extent possible. Since this involves aesthetic preferences upon which there is little agreement, such as shape and faceting styles, this is the most subjective of all aspect of quality analysis. Evaluation of cut involves five major factors:
This describes the girdle outline of the stone, i.e. round, oval, cushion, emerald, and etc. While preferences in this area are largely a personal choice, due to market demand and cutting yields, certain shapes fetch a premium. For ruby and sapphire, ovals and cushions are the norm. Rounds and emerald shapes are more rare, and so receive a premium from 10% t0 20% above the oval price. Pears and marquises are less desirable , and so trade about 10% to 20% less than ovals of the same quality. The shape of a cut gemstone almost always relates to the original shape of the rough. Thus the prevalence of certain shapes, such as ovals, which allow greatest weight retention.
The cutting style, facet pattern is also a rather subjective choice. Again, because of market demand, manufacturing speed and cutting yields, certain styles of cut may fetch premiums. The mixed cut, brilliant crown/step pavilion, is the market standard for ruby and sapphire.
If a gem is cut too shallow, light will pass straight through, rather than returning to the eye as brilliance. This term is called a “Window”, shown in the picture below. In well cut gemstones, most light return as brilliance. Brilliant areas are those showing bright reflections. Extinction is used to describe dark areas where little or no light return to the eye.
The faceted cut for ruby and sapphire is to create maximum brilliance scintillation in most symmetrical pleasing manner. Faceted gems feature two parts, crown and pavilion. The crown’s job is to catch light and create scintillation and dispersion, in case of a diamond, while the pavilion is responsible for both brilliance and scintillation.
when the crown height is too low, the gemstone lacks sparkle. Shallow create windows, while overly deep pavilions create extinction. Again, proportions are often dictated by the shape of the rough material. Thus to conserve weight.
In attempting to quantify a gem’s preparations, reference is often made to depth
percentage. It is calculated by taking the depth and dividing it by the girdle
diameter, or average diameter, in the case of fancy shape (not round)
stones. The acceptable range is generally 60% to 80%.
Length to width ratio
This measurement is used for fancy shape gemstones. Overly narrow or wide gems
of certain shapes are generally not desirable.
Like any fine crafted product, well cut gemstones display an obvious attention to detail.
A failure to take proper care evidences itself in a number of ways, including the following:
Asymmetrical girdle outline
Off center culet or keel line
Off center table facet
Overly narrow/wide shoulders, Pear and Heart shapes
Overly narrow/deep cleft, Heart shapes
Overly thick/thin girdle
Poor crown/pavilion alignment
Table unparalleled to girdle plane
Lack of care in the finish of gemstones is less of a problem than the major symmetry
defects, because it can usually be corrected by simple polishing. Finish defects includes:
While these guideline may be helpful, but one must not become a slave to them. In essence, the cut should display the gemstone’s beauty to best advantage, while not presenting mounting or durability problems. If a gemstone is beautifully cut, things such as depth percentage or length to width ratio do not matter one bit. What works, works.
Influence of lighting on color
With any color gemstones, the color seen depends on the light source used to illuminate it. Most gems traders have come to rely on skylight for their gemstones buying. Its advantage is its strength, which reveals flaws. The light coming through even a modest sized window is far greater than the strongest, color balanced fluorescent tube. North daylight, skylight, as oppose to direct sunlight, has becomes the standard. Some type of artificial light lamp is designed to stimulate the north day light. Today, many dealer purchase their gemstones under the special day light lamp.
Carat is a metric unit of weight used to measure the weight of a gemstone. One carat is equal to 1/5 or 0.20 grams
Different Gemstone have different densities, mass per unit volume, so two gems that appear to be the same size may actually have different weights. As an example, A ruby is more dense than a diamond, therefore a one carat ruby will look smaller than a one carat diamond of the same dimensions. The Jewelry Hut provides the diameter dimensions for all round shaped gemstones or the length and width for all other fancy shaped gemstones. This will help you to choose the right size or carat weight gemstone for setting on a ring or other jewelry items. To determine the right carat weight gemstone for your jewelry item, refer to the Gemstone weight chart shown below.
Viewing Geometry and background
Gemstone are designed to be mounted in jewelry and viewed from predetermined angles. This is usually faced up, with the stone viewed in a 180 degree arc from girdle to girdle. Thus it is only logical that all quality determinations be made with the unaided eye under the same viewing geometry. It is important that the stone be rotated through 360 degree in the girdle plane, so that its appearance is seen from all angles, just as it would be when mounted in jewelry.
To ensure reproducibility and repeatability, a standard light source against a standard neutral background, white is the best, at a standard distance should be used. The practice of grading a diamond body color through the pavilion has no place in color gemstones grading.
In grading any gemstones, one must be cognizant of, but not lost in, the details. Fine precious stones are comparable to great works of art. Like a painting, to appreciate it, one must view the whole, not just parts.
Cost of precious gemstones
Price is directly related to quality, weight, and rarity of a color gemstone. Market factors can have as much, or greater, impact on prices as does quality. The following factors influence the price of a gemstones:
Quality, Better qualities are more rare than the lower qualities of the stones in the
Weight, The bigger stone are more rare, and so more expensive per carat than the
same quality of a smaller size
Market Factors, This is the great intangible. Market factors, i.e. the supply and
demand, can dramatically affect price of a fine gemstone
Finally, the fifth C, The Jewelry Hut Confidence. The jewelry Hut has trustworthy professional jewelers who establish personal relationship with our valued customers and take pride in finding quality color gemstones for you. These experts are knowledgeable and accessible and are able to explain any question you may have and provide you with The Jewelry Hut 5th “C”, Confidence. When you, our valued customer, purchase a precious color gemstone from The Jewelry Hut. you can be confident you are getting what you are paying for.
Almost all color gemstones are enhanced. Enhancements such as heating are an expected part of the polishing and finishing process.