Jérôme Jabès Bijoutier, Joaillier, Diamantaire

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Emerald

GEMOLOGICAL PROPERTY CHART

The legends

The most famous legend is about the Chief El Dorado, and comes to us from Columbia. El Dorado was an Indian chief who, once a year, smeared his body with honey and then covered himself in gold powder. Then, rowers would tow him on a raft to the center of a volcanic lake called Guatavita, seventy kilometers north of Bogota. The rowers had to turn their eyes away from him, because nobody was allowed see him in his magnificent glory. At the first glimmer of day, El Dorado would plunge into the lake, letting all the gold dust wash off, in an offering to God. At that moment, all along the shore, his people would throw offerings into the water, according to their rank in society. The richest would toss their emeralds and gold into the waves.

Emerald Mines

Emeralds from Columbia comprise about 50% of the worldwide production and 80% of the emeralds of highest quality. The veins are located in the Cordilleras of the eastern Andes, in the Boyaca region. They are divided into two principal zones. One in the Muzo National Reserve, Coscuez and Pena Blanca, 120 kilometers north of Bogota, on the eastern slope of the Cordilleras in the direction of Magdalena valley, The other including Chivor, Somondoco and Gachala, 100 kilometers north-east of Bogota on eastern slope of the Cordilleras facing the great ìllanosî oil plains.
Emeralds crystallized in extremely unique conditions in each strata they are found, in regions as diverse as Columbia, Brazil or Pakistan. Surprisingly, the different geological environments produce emeralds that look identical.

From Rough to Polished

Rough Emeralds

The varying strength or fragility of emerald is caused by the fact that rough emeralds are extracted in their site of crystallization, whereas the corundum family of gems are usually found in the alluvium, sometimes very far from the original site of crystallization.
The rough emeralds are almost systematically oiled to be sorted and displayed when sold. The oil must be removed before any cutting.
The cleaning can be more or less important depending on the mine of origin. It may be rubbed with an acid solution to remove the oil.

Color

The color is not uniformly distributed in most emeralds. The first cutting is crucial: the future look of the gem depends on it.
With and emerald, what matters most before anything is the color. An emerald is saturated with color when it is rich in chromium, and it will show the maximum green. However, it can be too colored, making the stone darken and seem almost black.
There is a difference in color according to the angle from which one looks: from strait on, an emerald appears yellow-green. From the side, it appears blue-green. Because of the preparation, the lapidary should choose carefully to find the best overall solution: color, dimension, and characteristic.
In the end, the color is not always uniform. One frequently finds a section of color variation in a hexagonal shape, or a nearly white center.

Purity

A pure emerald is extremely rare. The rocks frequently contain random fine inclusions, without any order of which we call gardens. In a large number, they hinder the transparency and brilliance of the stone. Large emeralds are often very poorly carved in a half-oval form, and classified as rough emeralds, these are called "cabochons". The frequent presence of "gardens" can make the emerald fragile and effectively porous.
The positioning of an emerald on a piece of jewelry depends on displaying the best color, but one should also be careful to place the gem in such a way as to avoid displaying the "gardens". Therefore, the defects are best situated on the periphery of the stone.

The Creation

The lapidary should be careful in selecting a cut for an emerald, and should consider the natural shape of the stone. Possible cuts include: octagonal, oval, pear, etc. There is a risk in cutting against the properties of the gem. The cuts should be made with an extremely fine diamond blade.

The cut

An emerald loses between one-half to three-quarters of its weight when cut. Stones are first worked by the chief cutter, according to the specific properties of the merchandise. The procedure consists of centering the color of the emerald and cut so as to optimize the stones defects and color placement. Then the facets of the cut emerald are polished again in order to locate the defects and correct them, and to determine the orientation of the final stone. Then they are placed with hot wax on top of a stick. The lapidary proceeds to cut the facets and tables before giving the gem its final polish.

Emeralds are frequently found in hexagonal form, which has inspired the cut named "emerald cut". The rough emerald is cut through the middle, resulting in two parts which have dimensions very close to the desired form, which wastes much less of the total mass. Unfortunately, the final color will be green-blue. Even though there are advantages, the color isnít as highly prized as green-yellow.
Connoisseurs prefer a small stone of very beautiful quality over a large stone of mediocre quality.
The lapidary may also modify the tint of a stone when working on the facets. A stone that is toodark can be lightened by cutting it with a large table. Inversely, a stone can appear darker if it has a small table and many facets

The finish

After the final cut, the stone is polished. The choice of abrasive material is very important. An emerald with many facets is polished under a pewter grindstone, covered with a aluminum powder, fine diamond powder, or chromium oxide. The cabochons are usually polished under a wheel of felt with aluminum powder. The polishing restores the brilliance of the stone dulled by the by the grains of diamond used during the cutting process. Surprisingly, polishing is much more delicate than cutting. This is because, primarily, emeralds are fragile, but frequently, the strength of a stone is compromised by any "gardens" on the surface. Sometimes, polishing oil gets inside the gem, blackening the stone. These black traces in the "gardens" are difficult to clean even with acid.
After the cutting and polish, a final bath of oil is necessary. The stone is heated and any "gardens" will become visible as white reflections. Oil or certain types of very light resins work well to fill these gaps, the best remain uncolored and do not compromise the color of the emerald. Generally, each lapidary has his own special oil, and his own way of bathing the stone that is kept as a trade secret.

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