Emeralds, with their rich, green hue and captivating allure, have fascinated humans for centuries. They belong to the beryl family of minerals, which also include aquamarine and morganite. Emeralds are often distinguished from similar green stones like peridot or garnets by their distinctive, deeply saturated green hue. This deeper green color of emeralds is primarily due to trace amounts of chromium and sometimes vanadium within the crystal structure. Emerald mines are typically found in countries such as Colombia, Zambia, Brazil, and Afghanistan, with the Colombian mines of Muzo being renowned for producing some of the finest specimens while the emerald mines of Zambia produce high-quality emeralds, known for their rich green color.
Beyond their physical beauty, emeralds have been cherished for their mystical properties and significance in astrology. In various cultures, emeralds are believed to bring the wearer balance and harmony and improve memory, and intuition. Like yellow sapphires, blue sapphires, and hessonite garnets, emeralds are part of the famed Navratna gemstones. In Vedic astrology, emeralds are associated with the planet Mercury and are worn to improve communication skills, and intellectual abilities, and to protect against negative energies. Additionally, emeralds hold the esteemed position of being the birthstone for May, symbolizing renewal, growth, and vitality.
However, most natural emeralds have inclusions and fractures that can affect their beauty and durability. This is particularly true for emeralds from Zambia, known for their intense greens but also for containing a higher density of these internal characteristics. To elevate their appearance, many emerald stones undergo oil treatment. This article explores the fascinating world of oil treatment in emeralds, shedding light on its history, techniques, and implications for both gemologists and consumers.
An Uncut Emerald Stone
What Is Emerald Oil Treatment?
Emerald oil treatment is a centuries-old practice refined and standardized by modern science to enhance the clarity, brilliance, and durability of emeralds using natural oils and resins without altering the gemstone's structure or value. Most emeralds, naturally prone to inclusions and imperfections known as "jardin", have microscopic fissures and fractures that can mar their beauty. This oil treatment acts as a guardian of gemstone perfection, filling these tiny cracks with colourless oils, to improve clarity and brilliance.
Emeralds are a rather inclusive category of gemstones (Source: GIA)
Over 99% of all emeralds on the market are oiled, making it the most common and accepted treatment for these gemstones. Most gemological laboratories acknowledge this treatment in their certificates, emphasizing that oiling does not harm the emerald, alter its chemical composition, or affect its longevity. In contrast, untreated "no-oil" emeralds are exceptionally rare and highly valuable. While "no-oil" emeralds are the most desirable for their natural quality factors, minor oiling is widely accepted and common. Emeralds treated with synthetic resins are generally less valuable and not as desirable due to the less natural enhancement they provide.
Why Are Emeralds Treated With Oil?
Natural emeralds typically contain numerous inclusions and fractures, known as "jardin" (French for garden), which can detract from their visual appeal. These inclusions are a result of the complex geological processes that form emeralds, involving high temperatures and pressures over millions of years. Oil treatment addresses these imperfections by filling the fractures with oil, thus reducing their visibility and intensifying the stone's transparency. This improvement in clarity not only makes the emerald more attractive but also significantly increases its market value, especially in the jewelry industry. By making the internal flaws less noticeable, oil treatment allows more emeralds to meet the aesthetic standards desired by consumers. Oil treatment is also sometimes applied to opal stones to prevent them from drying out over time.
An Emerald before & after oil diffusion (Source: GGTL Labs)
Common Oils Used in Emeralds
Let's delve deeper into the types of oils used and the treatment process itself.
1. Natural Oils
The effectiveness of natural oils in enhancing emeralds lies in their refractive index, which determines how light behaves when passing through a material. Natural oils, such as cedarwood oil, closely match the refractive index of emeralds. This close match allows light to pass through the filled fractures more seamlessly, thereby minimizing their visibility and enhancing the clarity of the stone. Moreover, the application of oil can also improve the emerald's color saturation by reducing light scattering within the gemstone.
- Cedarwood Oil: The industry standard due to its effectiveness and long history of use in gem treatments. Cedarwood oil is particularly prized for its ability to blend seamlessly with the emerald, minimizing the visibility of fractures and inclusions.
- Palm Oil: Occasionally used as an alternative to cedarwood oil. Palm oil has a slightly different refractive index, but it can still effectively reduce the appearance of fractures in emeralds.
- Canada Balsam: A traditional substance used in gem treatments, Canada balsam is a natural resin obtained from the balsam fir tree. It has a refractive index close to that of emeralds and is used to fill fractures, making them less visible. Canada balsam is particularly valued for its historical use and natural origin, although it is less commonly used today compared to cedarwood oil.
2. Resins
In addition to natural oils, synthetic oils and resins are also used to treat emeralds. These materials can offer more durability and longer-lasting results compared to natural oils, which may dry out or degrade over time. However, resin is generally less desirable than oil because resins like Opticon can turn yellow over time, affecting the emerald's appearance. Oils are easier to remove and replace than resins, making future treatments simpler. Additionally, oils penetrate the stone more thoroughly, offering a more natural appearance. Collectors and jewellers also prefer oil-treated emeralds, impacting the stone's value and desirability.
- Polymer Resins: These synthetic materials provide a more permanent solution than natural oils. Polymers can fill fractures more thoroughly and do not evaporate or degrade as quickly as natural oils. However, they can be more difficult to detect and may require advanced testing methods.
- Epoxy Resins: Epoxy resin is commonly used in the production of synthetic quartz and quartz compositions. They can provide a permanent fill for fractures, but they may alter the appearance of the emerald if not applied carefully.
- Opticon Resin: A specific type of polymer resin commonly used in the gemstone industry. Opticon is designed to penetrate deeply into fractures and provide a durable, long-lasting fill that improves the gemstone's clarity.
The Process for Oiling Emeralds
The process of oiling emeralds involves several steps to ensure that the treatment is effective and durable.
- Cleaning: The first step involves cleaning the emeralds to remove any surface impurities, oils, or residues. This is typically done using a mild detergent and warm water, followed by a thorough rinse and drying.
- Inspection: After cleaning, the emeralds are inspected under magnification to identify the fractures and inclusions that need treatment. This detailed examination helps gemologists determine the extent of the treatment required and plan the application process accordingly.
- Heating the Oil: Some treatments also involve gently heating the oil before or during the immersion process. Heating the oil reduces its viscosity, making it flow more easily into the fractures. This step can improve the penetration of the oil and ensure a more thorough fill of the fractures.
- Oil Immersion: The cleaned emeralds are then immersed in the chosen oil. This can be done under normal atmospheric pressure, where the emeralds are simply soaked in oil for several hours or overnight. The exact soaking time may vary depending on factors such as the type of oil used, the size and shape of the emeralds, and the desired level of clarity enhancement. Sometimes, oil immersion may also take place in vacuum chambers. This process involves placing the emeralds in a chamber where the air is removed, creating a vacuum. This vacuum removes air bubbles trapped within the fractures, allowing the oil to penetrate more deeply and fill the fractures. The vacuum method ensures that the oil reaches even the finest cracks, providing a more uniform and effective treatment. The emeralds are usually soaked in oil for a longer period, often several days or even weeks, to ensure the oil penetrates deeply into the stone and fills the fractures effectively.
- Wiping Excess Oil: After the oil has penetrated the fractures, the emeralds are removed from the oil and any excess oil on the surface is carefully wiped off. This step is important to ensure that the oil treatment does not leave a residue on the surface of the emerald, which could affect its appearance and feel.
- Curing: In some cases, the treated emeralds are gently heated to help the oil set and bond better within the fractures. This curing process can improve the durability of the treatment, ensuring that the oil remains in place for a longer period.
- Final Inspection: After the oiling process, the emeralds undergo a final inspection to ensure the treatment has been successful and that the fractures are adequately filled. This inspection helps identify any areas that may need further treatment and confirms the overall improvement in clarity and appearance.
By following these detailed steps, the oiling process effectively elevates the beauty and value of emeralds, making them more appealing to consumers and collectors alike. The use of vacuum pressure and heating are significant advancements over ancient methods, providing deeper penetration and more permanent results. As a result, oil-treated emeralds today can display remarkable clarity and brilliance, making them more desirable in the market.
Identifying Oil-Treated Emeralds
Identifying an oil-treated emerald can be challenging to the untrained eye, but certain clues such as trapped air bubbles or an overly glossy appearance can indicate treatment. Gemologists use microscopes to detect the presence of oil in fractures. Under magnification, treated fractures may show a flash effect—a sudden change in color or brightness when the stone is rotated—due to the difference in refractive index between the oil and the emerald. Advanced gemological laboratories employ techniques like infrared spectroscopy and UV fluorescence to identify oil treatments definitively. These methods can detect the specific substances used in treatment, providing a more accurate analysis.
Alternatives to Oil Treatment
Other treatments, such as resin filling and polymer impregnation, offer alternatives to traditional oiling. Resin filling involves filling the fractures in the emerald with a specially formulated resin that hardens to provide a more durable and long-lasting enhancement. Similarly, polymer impregnation involves injecting a polymer substance into the fractures, which then hardens to strengthen the gemstone's structure. While these methods can offer enhanced durability compared to oil treatments, they may also be more detectable under magnification and are considered less traditional in the gemstone industry.
Making an Informed Choice
The gem industry has established standards and guidelines for the disclosure of oil treatments. It is considered unethical to sell an oil-treated emerald without informing the buyer of the treatment. Certification services provided by gemological institutions, such as the Gemological Institute of America (GIA) and the American Gem Society (AGS), include treatment disclosure. A certified report will indicate whether an emerald has been treated and, if so, the extent of the treatment. Typically, they use a grading scale to indicate the presence of oil. In general, most gem labs use a variation of the following scale to comment on the amount and nature of an oil-treated emerald:
- Insignificant Oil: The least amount of oil detectable, with minimal impact on clarity.
- Minor Oil: A commonly accepted practice with a slight enhancement in clarity.
- Minor-to-Moderate Oil: A moderate improvement in clarity using a slightly greater amount of oil.
- Moderate Oil: A noticeable enhancement in clarity, with a more significant amount of oil used.
- Prominent Oil: The most oil present, with a substantial impact on clarity. This grade might affect the stone's value.
A GIA Certificate of an Emerald - stating that clarity enhancement is a common trade practice
The lower the grade on this scale, the less oil is present, indicating minimal enhancement. Consumers should always ask for certification when purchasing emeralds and be aware of the potential treatments applied to the stones. Being informed helps buyers make educated decisions and ensures they understand the value of their purchase.
Allure of No-Oil Emeralds
For those who value complete naturalness, no-oil emeralds from Zambia and Colombia hold the highest esteem. These gems, with their inherent inclusions and fractures, are prized for their authenticity and rarity. Collectors and connoisseurs often seek out untreated emeralds, appreciating their untouched beauty and willing to pay a premium for a larger-carat stone in its natural state. The decision between a treated and untreated emerald ultimately comes down to personal preference and budget.
In the intricate world of gemstones like emerald and peridot, oil treatment stands as a pivotal process, enriching the allure and marketability of these birthstones. This technique not only enhances the gem's aesthetic appeal but also expands its accessibility to a wider audience of admirers. By delving into the intricacies of oil treatment, understanding its implications, and familiarizing oneself with the necessary care, consumers can navigate the realm of emeralds with confidence and discernment. Whether drawn to the brilliance of treated stones or the natural allure of untreated ones, an informed decision ensures a gratifying ownership experience. Ultimately, appreciating the craftsmanship behind oil-treated emeralds enriches the journey of owning and cherishing these captivating gems, whether they are destined for elegant jewelry pieces or sought after for their significance in astrology.
