The Emerald Story

The main cuts employed for emeralds

Step/Emerald cut: This is the most important and popular cut employed for emeralds. All facets are cut in squares or rectangles which are arranged in steps, giving an elongated octagonal outline. The best quality emeralds are almost universally fashioned in this way for these reasons:
- It shows the saturated deep velvety-green of emerald to the best advantage. Since color is the most important determinant of value in emeralds, a stone with a good depth of color fetches a higher market price than one that does not.
- The step cut minimizes loss of mass during cutting and polishing. This means more carat weight retention of the stone and hence value (value = price/carat x carat weight).

Mixed cut: The crown of the stone is brilliant cut, while the pavilion is step cut. It is not very popular since it gives the stone a pale glassy look, which is not desirable.

Cabochon & beads: Stones which are turbid and heavily included and are of good color are commonly cut as cabochons and beads. A cabochon may have a flat base and a dome-shaped upper portion. Emeralds cut in this manner are usually sub-transparent to opaque, and can range from light to very dark green. Emeralds of low to medium quality are thus fashioned. Emerald beads and cabochons are becoming increasingly popular since they are a beautiful yet inexpensive form of natural emeralds.

Fancy cuts and carvings: Heavily included emeralds with good color but limited transparency are an excellent base for carving. Carved emeralds are fashioned into pendants, belt-buckles, and show pieces in a variety of exotic jewelry.

The cut of a stone is crucial to its color and beauty, and has great influence on its ultimate value.

Common treatments applied to emeralds
Mining, cutting, faceting, and polishing procedures are accepted and considered, as the normal processing of gemstones. However, in his endeavor to enhance value, man has subjected his gems to further treatments. Some of the treatments are necessary and are now accepted as normal processing for a gemstone, while others are subject to disclosure.

The common treatments for emeralds are oiling, staining/dyeing and resin impregnation.

Oiling: Perhaps the most universal treatment for emeralds, practised by emerald dealers all over the world. This treatment is more of a finishing touch applied to emeralds of good color but with visible internal fissures. Oiling enhances surface shine and luster, and reduces the visibility of fissures in the stone, thereby adding to its saleability.

Oils used: Cedarwood oil, Canada Balsam, mineral oil.

Method: The method of oiling varies from dealer to dealer, with much being kept secret for obvious reasons. But basically, it involves these steps: (a) Emeralds are first cleaned thoroughly using a mild acid (b) They are then soaked in warm clear oil (Cedar oil is popular) and subjected to appropriate heat and sometimes pressure or vacuum.

Effect: The oil permeates into the fissures and fills them, reducing their visibility. Modern oiling machines offer an easily and effective treatment method for emeralds.

Durability of treatment: The oil comes out of the fissures when subjected to heat, ultrasonic cleansing, immersion in soapy water or acids, alcohol or other solvents. Otherwise, for normal wear and tear, it remains stable for a reasonable period of time. Stones can be re-oiled if necessary.

The practice of oiling is so prevalent that it is hard to curb. It is regarded as standard practice. But since the effect is not 100% permanent, trade organizations and gem testing laboratories encourages disclosure of the treatment to customers upon purchase.

Detection of oiling under the microscope: Traces of oil may be seen in fissures when the stone is viewed under the microscope. Typical signs of oiling are:
- Low relief of fissures that would otherwise appear white. Some fissures tend to appear shiny (fluid-like) when viewed at certain angles.
- Flattened gas bubbles trapped in the filling media (oil)
- Some oils fluoresce (emit light) when subjected to ultra-violet (UV) radiation. For e.g. Canada Balsam shows a weak greenish yellow light under UV.

Staining/dyeing: Yet another age-old technique to enhance the appearance of a gem that is commonly applied to emeralds. Whereas the main motive for oiling an emerald is to conceal fissures, the main aim of dyeing an emerald is to give a false appearance of color in otherwise pale-colored emeralds. The dyeing of colorless beryl to simulate the appearance of emerald is also carried out. Staining or dyeing may be either a surface only treatment or it may penetrate fissures.

Dyes used: Natural organic dyes, synthetic dyes (e.g. aniline) compounds of metallic salts.

Method: (a) The stone is thoroughly cleaned. (b) The stone is soaked in oil containing the green dye at an appropriate temperature for a few hours.

Effect: The green oil permeates into the stone increasing depth of color, and reducing the visibility of internal fissures.

Durability of treatment: Natural organic dyes are least stable and some deteriorate easily. Synthetic dyes tend to last longer. Certain dyes don’t come out of the fissures even if the oil wears off when subject to heat or alcohol.

Status of treatment: Since dyeing significantly alters the appearance of emeralds and possibly other beryls and is not permanent, this treatment should be disclosed to customers upon purchase.

Detection of treatment: One can always detect the presence of dye under magnification. Indications are: (a) Color concentration in fissures and chips, (b) Slightly colored outlining of fissures, (c) Uneven color distribution, (d) Some colored oils fluoresce under UV radiation.

Resin impregnation of fissures (Opticon treatment): A relatively recent development in the treatment of emeralds. It involves impregnating fissures with a synthetic resin marketed as Opticon. Opticon, as a resin, is more durable than oil, making the treatment more permanent. It is a two part product consisting of the resin itself plus a separate hardener (an additional fluid which when added to the resin causes it to become hard). A vacuum is usually used to assist the flow of the resin into the fissures in emerald. Sometimes the treater will then add the hardener and sometimes not.

Detection of the treatment: Many resins, including Opticon can be detected by the observation of blue and yellow/orange color flashes coming from the region of treated fissures. Positive identification can come from Raman spectroscopy available only in the best equipped gem labs.

Status of treatment: If no hardener is applied, whilst this resin treatment might be a little more stable than oiling it is still not permanent. If a hardener is applied this may cause fissures to expand under warm conditions, or when being repolished, which may result in severe damage-occurring. Hence, disclosure of treatment is required.

Emerald Story (continued)