In the business of enhancing emeralds, there are many oils, resins, and polymers commonly referred to and used when enhancing an emerald. According to the GIA, the following definition of substances and their characteristics will clarify some contradicting misinformation and educate the industry about the actual properties of commonly used enhancement substances.
Oil: Oil originally meant olive oil, which is not generally used in emeralds today. Its common meaning is one of "numerous unctuous combustible substances that are liquid or at least easily liquefiable on warming, are soluble in ether, but not in water, and leave a greasy stain on paper or cloth." (Webster's Dictionary, 1987)
Essential Oil: Some compounds, such as cedarwood, are "essential oils." These compounds are extracted from their host plants using solvents. According to the Polymer Science Dictionary (Alger, 1989), an essential oil is the predominantly volatile material isolated by some physical process from an odorous single-species botanical. The main components of many essential oils have been synthesized (again, including cedarwood oil) and commercial essential oils may be partially or wholly synthetic. Because of their volatility, open containers (such as an emerald) of essential oils cannot be stable over time, since the fragrant components are continuously lost in the atmosphere (or they would not reach our noses to be smelled).
Resin: Resin originally meant pine sap. Today, resin can mean at least three different things: natural plant exudate (i.e. saps), either hardened or unhardened; hardened manufactured polymers; or the unhardened prepolymer, building blocks that can be used to make manufactured (Webster's 1987, Stecher et al., 1968; Alger, 1989). Natural resins can harden (polymerize) over time (e.g., amber, copal). The emerald filler Canada Balsam is generally considered a natural resin, and the essential oil cedarwood oil is considered a resin.
Polymers and Prepolymers: A polymer is a large molecule made up of repeating units of smaller molecules. The smallest such unit is a monomer. The term "prepolymers" is used to describe the small units that are assembled into polymers, since they could be either monomers or a few monomers attached together. They polymerize, or harden, with the use of a chemical catalyst, illumination, heat, or time.
On the basis of the findings presented here, GIA recommends the following terminology:
- The term "natural" should be avoided in discussions of emerald fillers, as "natural" substances are not currently distinguishable from their chemical equivalents that are synthesized in the laboratory.
- The term synthetic should be avoided, as it does not have the same meaning in chemistry that it has in gemology.
- Prepolymers and polymers should be distinguished wherever possible, as their different mechanical properties are probably significant (e.g., liquid versus solid states), and many affect their durability in an emerald.
- Artificial resins should not be called "epoxies" unless they contain epoxide groups, if still liquid, or were joined into polymers with these groups.
- Because a large quantity of one filler may make small amounts of another undetectable, GIA recommends restricting comments to the filler identified, and making no assurances that any others are absent.