On to the topic of the day, gemstone cuts! I'm sure you're familiar with the 4 C's of Diamonds - Color, Cut, Clarity, and Carat weight. The same basic principles apply to most gemstones, and hopefully by the end of this blog you'll have a better understanding of not only the most popular cuts and shapes of gemstones, but you'll understand how the Color and Clarity helps determine the best choice of cut for any rough gemstone. I'm not ignoring Carat weight - I will also touch on the effect of a poor cut choice on the weight of the finished stone, but that is somewhat incidental to the real topic.
I want to clarify something before we delve too deep. Don't mistake the "shape" of a gemstone with its cut. Shape refers to the face-up outline of the gem. In other words, if you're looking at the top of the stone, the "shape" would be the general form it takes. Most common is the round or oval shape, although there is more and more marketing of non-traditional shapes. Rectangle, triangle and pear shapes have been popular for awhile now, as well as marquise, heart and even cushion shapes. Today some gem-types are even left in semi-natural state, or cut in fanciful designs.
The "cut" of a gemstone actually refers not to its shape as many people believe, but to its proportions, such as its depth and width and the uniformity of its facets--all characteristics that control brilliance, durability and other features we look for in a gemstone. There are three basic faceting cuts - the Brilliant cut, the Step Cut, and the Mixed Cut.
Colorless, sometimes called White, Diamonds are the standard of color against which every other gemstone color is judged. These diamonds are unique in that their lack of color creates a maximum combination of three effects: brilliance (return of light), dispersion ('fire'), and scintillation (a twinkling effect). I think before I try to explain those effects, I need to familiarize you with some terms. Take a look at this diagram and refer to it if you need to.
Brilliance is provided for the most part, by the pavilion facets. These catch the light rays and throw them back to the eye.Dispersion is a result of the prism effect of the crown facets. These split white light into its spectral components - similar to sunlight creating a rainbow.
Scintillation is achieved by breaking large facets up into smaller ones during the cutting process to create a twinkling effect when either the eye, the light or the stone is moved.
A well cut, quality diamond should easily produce all of these effects. Add color to the stone tho, and the gemstone's ability to disperse light is affected, which is why most colored gemstones are cut to show off their brilliance and scintillation. If you look closely straight down into most faceted colored gemstones, you will commonly see three different color variations in the stone. You will see the brilliant true color of the stone, slightly less brilliant areas and areas that appear dark. While these may be extremely minor differences in a well cut stone, in a poorly cut stone they can be very pronounced. This is usually caused by the pavillion facets being cut at too shall
ow an angle.
ow an angle. This example will illustrate the difference. In the left hand stone, light is reflected back from the pavillion facets as brilliance. The right hand stone has much shorter pavilion facets - creating the effect of a "window" which allows the light to escape through the bottom of the stone, resulting in a much duller stone. Pavillion facets that are too long will allow light to escape through the sides of the stones, also dulling the brilliance. (Photo by Wimon Manorotkul/Palagems.com.)
A skilled lapidary will study a stone's shape, color, size, inclusions (the small imperfections that exist in virtually every natural stone), and whether it is transparent (light travels easily through it), translucent (light shines thru it, but not as "cleanly" as through a transparent stone), or opaque (light is blocked by the crystalline structure of the gemstone). By taking all of these factors into account, the lapidary will then be able to choose a cut that will highlight the qualities of that particular stone to their greatest extent.
Combining the right "cut" with the right "shape" is what makes the difference between say, a very refined and glamourous cocktail ring or wedding set with its finely cut stones, and an earthy uncut gemstone, popular in today's wire wrapped and very naturalist styles of jewelry.
Here are some examples of Gemstone shapes:
Round Brilliant cut - also known as the Round cut, American Ideal cut or American Standard cut. The standard number of facets for this cut is 57. The Round Brilliant cut is designed to provide maximum optics for brilliance and scintillation, making the gem sparkle and dance in the light. While this cut was originally developed especially for diamonds, it has become a common cut for all gem types.
Oval cut - has an elliptical shape when viewed from the top and the ratio of the length to the width should be approximately 2:1 A well cut Oval gemstone can be nearly as bright as a Round Brilliant cut. The standard number of facets of an Oval cut gemstone is 69.
Baguette - is from the Italian word “bacchetta”, meaning “rod or stick” - this is one of several oblong shapes used for gemstones. Most oblong cuts are “step” cut, which means that the facets on the pavilion have been cut in steps, parallel to the edges, in the manner of a pyramid with its top chopped off. The base and table are square with triangular facets. The approximate number of facets of a Baguette cut gemstone is 20.
Square shape -another step-cut oblong shape used for gemstones, however, unlike the Baguette, the sides are equal in length. The standard number of facets of a Square cut gemstone is 57.
Trillion shape - based on a triangular shape. Usually with truncated corners and displaying a variety of facet designs, this cut creates a spectacular wedge of brilliant fire. The tips and culets of Trilliants are pointed and thin. While many jewelers prefer to bezel set this shape, prongs that protect the tips work well and show more of the gem. Because of their equilateral form, Trillions return lots of light and color and are considered nearly as brilliant as Round cuts, so they are a great choice for people who like brilliance but want something other than round. Trillions work well with light-colored gems like Diamonds, Aquamarines, Beryl’s and White Sapphires. These are stones that, because of their light color, can be cut to maximize brilliance. This cut is also often used to lighten and brighten the appearance of darker gems such as Tanzanite, Spessartite Garnet, Rhodolite and Amethyst.
Pear Shape - this mixed cut shape combines the Oval with the Marquise, its shape resembling a teardrop. The standard number of facets of a Pear cut gemstone is 71.
Octagon shape - The standard number of facets for this gemstone cut is 53.This is another “step” cut but with the four corners cut off. Color tends to show very dramatically in Octagon cut gemstones.
Emerald shape - looks like a rectangle from the top. The approximate number of facets of an Emerald step cut gemstone is 50. The Emerald cut was developed specifically for Emeralds to reduce the amount of pressure exerted during cutting and to protect the gemstone for chipping as well as to highlight the dramatic color of the gem. Today, it is used for a wide variety of gem types.
Marquise or Navette shape - has the appearance of a long pointed oval (similar to a football or rugby ball). The standard number of facets of a Marquise cut gemstone is 57 and the ratio of length to width is ideally 2:1. Shallow cutting stones in this shape can lessen their brilliance, so look for stones that don't let too much light shine thru the bottom.
Antique Cushion (Old European, Pillow) shape - in appearance resembles a cross between a large faceted cut that was popular in the late 19th and early 20th centuries and the modern oval cut. This cut will maximize a gem's luster.
Princess cut (Square Modified Brilliant cut) is a square version of the Round Brilliant cut with sharp, uncut corners. This shape is usually deeper than most other shapes in order to maximize the brilliance of the stone. It generally has 76 facets. Originally devoped for diamonds, the Princess cut generally works best with lighter colored transparent gemstones.
Heart Shape - a pear-shaped gemstone with a cleft at the top and 59 facets. Its length to width ratio is slightly over 1:1, approximately 1.1:1 in favor of length, but usually not over 1.2:1. Hearts have to be extremely well cut which makes them more expensive because the cutting process results in a greater loss of rough stone.
Briolette shape - the most difficult to cut, the briolette is a pear shaped gemstone covered with facets that comes to a pointed end. The approximate number of facets of a Briolette cut gemstone is 84. The more facets the drop has, the more brilliant it is. The Briolette cut is a drop-shaped gemstone with triangular or diamond shaped facets all the way around. There is no table, crown or pavilion. Because of the specific number of cuts to show the facets, the Briolette cut must be perfect from top to bottom.
Cabochon - a polished gemstone with a flat-bottom (or slightly rounded bottom) and a convex or rounded domed top. The traditional Cabochon is an Oval but Cabochons can also be fashioned into virtually any other shape. Commonly known as Cabs, this shape is the oldest and most common form of gem cutting. Gems cut “en Cabochon” are shaped and polished, rather than cut. Cabs are usually created from gems of limited transparency like Turquoise, Jade, or Agate, or heavily included relatively opaque Sapphires, Rubies or Emeralds, or for gems where the cut’s curved surface accentuates special characteristics - like tiger's eye, star sapphires, cat's eye
Buff Top Cabochon - A Cab variant for transparent gems, this cut mixes a faceted cut with a non-faceted cut. This results in a gem with the typical domed top of a Cabochon and a faceted pavilion, giving the illusion of depth as the eye is drawn into the centre of the gem. The cut shows good brilliance and has a crown that is less easily abraded than those of faceted gems.
Fancy Cuts
In an effort to create a constant stream of new designs, unique shapes, and to find ways to bring out even more brilliance in gemstones, lapidaries are constantly experimenting with new cuts and shapes. There has been an incredible increase in these "Fancy Cuts" over the past few years, as customers search for that special one-of-a-kind gemstone. The possibilities, just like with most other aspects of jewelry design, are limitless. These are just a couple of fancy cuts that have found their place at the top of the list of newcomers.
Millenium - a cut created for the new millenium in 1999, this shap possesses an unbelievable 1,000 facets. This is a very rare cut.
Concave cut is a three dimensional conical shaped facet applied to the pavilion of the gem that creates depth as well as length and breadth. Instead of the facets being joined by an angle they are joined with a groove. This third dimension allows the gem to refract more light, thereby maximizing its brilliance. The Concave cut also distributes light more evenly, giving the gem an even interior glow. This cut usually works better with lighter stones than darker ones.
You'll find many of these lovely gemstone cuts and shapes throughout the great jewelry shops on Etsy, but here are just a few of my favorites!
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