Treatments & Enchancement
It is said as much as 99% of available emeralds are treated in some way. This is because the overwhelming majority of stones have minute surface reaching fractures. These natural inclusions are often treated to improve clarity, making untreated or insignificantly treated gems exceedingly rare and valuable.
As far back as Ancient Egypt, the process of fracture filling has been documented in scrolls and ancient texts. Unlike other colored gems that are typically treated with permanent methods of high heat and pressure to improve color and clarity, emeralds would be damaged by such processes. Typically, the preferred method to clarity enhance an emerald is through filling natural fissures and fractures with oils, although more permanent methods do exist. Natural cedar oil is traditionally used as it is colorless and does not interfere with the natural refraction of the gem, meaning light is able to pass through easily. A stone is gently heated to open its surface reaching fissures before being soaked in oil and sometimes treated at low pressure to encourage the oil to penetrate the gem, filling tiny cracks, purifying the tint and helping to conceal inclusions.
Many modern stones have been treated with polymer resins. Polymer is more resistant to wear and more stable however is considered a more extreme treatment. The most significant treatments involved colored polymer resin and oils that artificially enhance the stones hue where it is masquerading as a higher priced gem. It is important to note that the hue of these heavily treated stones does not match that of the actual emerald and the dye will likely fade over time. These type of treatments are generally frowned upon in favor of traditional oil treatments.
This being said, oil treatments are not necessarily permanent and stable. Time, heat or improper cleaning can cause the oil to evaporate, change color or leach out of the stone. Stones can be re-oiled if this occurs. Cedar oil is 100% natural, which is why it is the favored and most the traditional form of treating an emerald. A stone with a minimal amount of treatment should never require re-oiling; however, many dealers of low quality goods have begun using artificial hardened resins to fracture fill emeralds in the hope of providing a more permanent treatment to stones that require a lot of it. This is often undertaken before the cutting process to ensure that any rough stones that would normally have too many fractures, and therefore be too structurally weak are able to survive the pressure of the cutting and polishing wheel. Emeralds that are treated in this way are considered low in quality and value.
Treatments range from insignificant/minor oiling, to moderate and significant fracture filling treatments. It is important to note when purchasing an emerald that the treatment classification is not representative of the inclusions within a stone, but instead how much foreign substances have entered inside the crystal. The significance of treatment in a stone should always be disclosed to the buyer and the price should be reflective of the stones' natural rarity.