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Coating Treatment For An Emerald A drilled bead was sold as an emerald… but the reality was very different. Under magnification, the colour told the story. We observed green surface coating beginning to flake, particularly around the drill hole and edges areas where wear occurs first. Testing confirmed the material beneath: white topaz, not emerald. Surface coatings like this can appear convincing at first glance, especially in beads. But they are only superficial and can degrade over time, revealing the true stone underneath. 🔍 What to look for:
 Colour concentrations around drill holes Uneven or patchy colour Signs of surface wear or flaking At E.D.R – European Diamond & Gemstone Reports, we specialise in accurate gemstone identification and coating treatment detection. If something doesn’t look quite right, especially with emeralds, have it tested.

As a reputable gemmological laboratory based in London, we strive to inform and protect consumers in the gem-buying market. One of the treatments you may encounter when purchasing rubies is glass filling (also known as lead glass filling), designed to enhance the stone’s appearance and clarity. While this treatment can make a ruby look more appealing, it also raises serious questions about authenticity, durability and long-term value. Table of ContentsWhat Is Lead Glass Filling Treatment?3 Signs of Glass Filling in RubyWhy You Should CareGlass Filling Versus Other Ruby TreatmentsThe Importance of Certification What Is Lead Glass Filling Treatment? Glass filling, or clarity enhancement, involves introducing a glass-like substance into the fissures and inclusions of a ruby to improve its visual appeal. The process begins with heavily fractured, low-grade corundum that would otherwise be unsaleable. The material is cleaned with acid, then heated with a powdered glass that has a very high lead content. The lead glass melts, flows into every crack and, because its refractive index is close to that of ruby, the fractures all but disappear. This process is often conducted to mask imperfections, allowing lower-quality rubies to appear more valuable. The treatment first appeared in volume around 2004 and quickly flooded the market, so it is now one of the most common issues we see when examining rubies for valuation. While this technique can enhance the gem’s clarity and colour, buyers must understand its implications. 3 Signs of Glass Filling in Ruby When evaluating rubies, particularly those that appear unusually vibrant or eye-clean for their price, look for the following signs that may indicate treatment: Visible bubbles: one of the most telltale indicators is the presence of flattened gas bubbles trapped within the glass-filled fractures. These bubbles can vary in size and are often visible under 10x magnification. (Do not confuse them with the round gas bubbles seen in synthetic ruby, which sit in the crystal itself.) Yellow and blue flashes: look for flashes of colour that may indicate the presence of glass. These appear as the stone is tilted, along the planes of the filled fractures. Check whether these flashes reach the surface and look for any visible fractures on the external part of the ruby, as this is where the glass is introduced. Blue-green fluorescence: rubies, due to their high chromium content, typically fluoresce weak to strong red under UV light. When glass treatment is carried out, the glass itself can produce an unusual chalky blue to green reaction in the filled areas. Under higher magnification a gemmologist may also see a “flow structure” in the glass and, on the surface, a slightly different lustre where polished glass meets polished corundum. The Gemological Institute of America (GIA) has published extensively on these identifying features. Why You Should Care The presence of glass filling can significantly affect a ruby’s valuation. Treated stones are worth a small fraction of their untreated counterparts – often just a few pounds per carat – even though they may look impressive at first glance. Many trade bodies consider heavily filled material to be a composite rather than a genuine gemstone, and it must be sold with full disclosure. Durability is the other concern. Lead glass is far softer than corundum and is attacked by common household chemicals, lemon juice and even some jewellery cleaners. Repairs that involve heat, such as re-tipping a claw, can cause the glass to melt or turn cloudy. Additionally, repairs or restoration may permanently alter the appearance and longevity of the gem. Glass Filling Versus Other Ruby Treatments Not every treatment is equal. Traditional heat treatment is stable, permanent and widely accepted; minor residues of flux or borax in healed fractures are also commonly encountered. Lead glass, by contrast, is a bulk filler that can make up a significant proportion of the stone’s weight, which is why laboratories describe such material differently and why the price difference is so dramatic. The Importance of Certification Before making any purchase, ensure you obtain a valid report from a reliable, independent gemmological laboratory. This will provide transparency regarding the ruby’s treatment history and authenticity. At E.D.R – European Diamond & Gemstone Reports, we employ advanced testing techniques, including Fourier Transform Infrared Spectroscopy (FTIR), alongside microscopy and UV examination to accurately identify treatments like glass filling, and we state the result clearly on our Loose Gemstones Report. Remember, a well-informed buyer is empowered to make the best investment decisions. In conclusion, buy rubies with caution. Stay informed about the treatments available and always seek professional guidance. By doing so, you ensure the integrity of your precious gems and protect your investment for years to come. Contact E.D.R for expert analysis and assurance regarding the quality and authenticity of your gemstone purchases, or read more about the July birthstone, ruby.

This stunning emerald features a remarkable significant treatment, often characterised by a striking blue hue resembling the northern lights across its surface. In the world of gemmology, emerald treatments are the norm rather than the exception: most emeralds undergo some form of enhancement to improve their colour and clarity, so understanding what has been done to a stone is essential before buying or selling one. Table of ContentsWhy Are Emerald Treatments So Common?The Main Types of Emerald TreatmentsHow We Identify and Grade Emerald TreatmentsHow Treatment Level Affects ValueCaring for a Treated Emerald Why Are Emerald Treatments So Common? Emerald is the green variety of beryl and, unlike most other gems, it almost always forms with natural fractures and inclusions. Gemmologists affectionately call these internal features the stone’s jardin (French for garden). Because these fissures reach the surface, they scatter light and make the stone look paler and less transparent than it really is. Filling those fissures with a substance that has a similar refractive index to the beryl makes them far less visible, which is why emerald treatments have been carried out for centuries. The practice is accepted throughout the trade, provided it is disclosed. The Main Types of Emerald Treatments Emeralds are commonly oiled with natural oils or resins to fill in surface-reaching fissures and improve their appearance. The most frequently encountered fillers are: Cedarwood oil: the traditional filler. It is natural and considered the most acceptable, but it can dry out or leach over time and may need re-oiling. Natural resins: such as Canada balsam, which are more viscous than oil and tend to last longer. Artificial resins: epoxy-type polymers such as Opticon or ExCel, sometimes hardened with a catalyst. These are more permanent but are generally regarded as a more significant enhancement. Coloured fillers: oils or resins that have been dyed green to artificially improve the colour. This is a dye treatment and must always be declared. The image shows a magnified capture of the treatment. The unique blue lightning-like line marks an area where the filler has entered a fissure and produces a flash effect – a tell-tale sign that the stone has been clarity enhanced. How We Identify and Grade Emerald Treatments To accurately assess these treatments, we first use a loupe and microscope to determine the visible extent of treatment on the surface of the gem. Under magnification we look for flash effects (orange or blue flashes within fissures), trapped gas bubbles, flow structures and a whitish or cloudy residue where the filler has begun to dry out. Following this, when needed, we employ Fourier Transform Infrared Spectroscopy (FTIR) testing as a secondary method. Advanced FTIR testing is particularly effective because it can detect the presence of treatments that may not be so visible and can help identify whether the filler is oil or resin. Combining both methods allows us to classify the treatment level as minor, moderate or significant, and this is recorded clearly on our Loose Gemstones Report. This additional insight ensures we provide a comprehensive understanding of the gem’s treatment history. How Treatment Level Affects Value The degree of enhancement has a direct impact on price. An untreated emerald of fine colour is exceptionally rare and commands a substantial premium. A stone with minor oiling is the commercial standard, while moderate and significant treatments reduce value progressively, because the stone’s apparent clarity depends heavily on the filler remaining in place. Independent laboratories such as the Gemological Institute of America (GIA) and Gem-A use similar terminology, so a report that states the treatment level gives buyers and insurers a reliable basis for comparison. Caring for a Treated Emerald Because oils and resins can be damaged, treated emeralds need gentle handling. Never clean them in an ultrasonic or steam cleaner, avoid harsh detergents and solvents, and keep them away from strong heat, all of which can draw out or cloud the filler. A soft brush and lukewarm soapy water is all that is needed. If an older stone starts to look dull or whitish in its fissures, it may simply need re-oiling by a professional, which is a routine and reversible process. To learn more about the gem itself, read our guide to emerald, the birthstone of May, or compare it with other common gemstone treatments such as the heating of ruby and sapphire. For gem enthusiasts and professionals alike, understanding emerald treatments helps you appreciate both the stone and the craftsmanship behind it. Every emerald tells a story – what will yours reveal? If you would like yours examined, get in touch with our London laboratory. Feel free to share your thoughts and insights on emerald treatments in the comments below!

Corundum is a mineral species that encompasses two of the most coveted varieties in the gemstone market: sapphires and rubies. While sapphires can be found in a spectrum of colours, rubies are specifically defined as red corundum, exhibiting a distinct hue due to the presence of chromium. One of the most prevalent methods for enhancing these gemstones is heat treatment, a process that significantly modifies their physical and optical properties. Table of ContentsWhat Is Corundum and Why Is It Heat Treated?How Heat Treatment Changes Ruby and SapphireHeat-Expanded Crystals and Fracture Halos in CorundumOther Signs of Heat TreatmentHow Gemmologists Test for Heat TreatmentWhy Corundum Treatment Disclosure Matters What Is Corundum and Why Is It Heat Treated? The mineral is crystalline aluminium oxide (Al2O3). In its purest form it is colourless, but trace elements such as chromium, iron and titanium give rise to the reds of ruby and the blues, yellows and pinks of sapphire. Ranking 9 on the Mohs scale, it is second only to diamond in hardness. Much of the rough mined today is pale, cloudy or unevenly coloured. Heating can dissolve silk, improve transparency and deepen or lighten colour, which is why the vast majority of commercial ruby and sapphire on the market has been heat treated. The treatment is stable and widely accepted, but it must always be disclosed. How Heat Treatment Changes Ruby and Sapphire Heat treatment involves exposing corundum to elevated temperatures, typically ranging from 1,200°C to 1,600°C, resulting in notable changes within the crystal structure. Less common treatments can occur at temperatures as low as 800°C and as high as 1,700°C. This process can lead to the formation of heat-expanded crystals, which serve as critical indicators of whether a stone has undergone enhancement. Furthermore, inclusions such as silk (rutile needles), fingerprints and colour zoning can be diminished or altered during heat treatment, potentially transforming the stone’s overall appearance. Heat-Expanded Crystals and Fracture Halos in Corundum During the heat treatment process, the crystal lattice of corundum expands, influencing the visibility and nature of internal inclusions. Mineral inclusions, such as other crystal fragments, expand at a different rate to the host and may develop distinctive fracture halos around them due to the thermal stress induced by the heat, as illustrated in the accompanying images. These halos can resemble an explosion effect, with the surrounding material appearing fractured and radiating away from the inclusion. The presence of heat-expanded crystals, along with these characteristic fracture halos, can often be observed under a microscope, providing clear evidence of the stone’s treatment history. While such fracture halos are strong indicators of heat treatment, it is important to note that they can also occur in untreated stones, albeit rarely. Careful examination of all inclusions is therefore essential before a conclusion is reached. Other Signs of Heat Treatment Heat-expanded crystals are rarely the only clue. When examining a ruby or sapphire, a gemmologist will also look for the following features: Altered silk: rutile needles that appear dotted, broken or partially dissolved rather than long and continuous. Discoid fractures: flat, disc-like tension fractures surrounding small included crystals. Chalky fluorescence: a chalky blue or green glow under short-wave ultraviolet light, often seen in heated blue sapphire. Colour zoning: diffuse or blurred colour banding where the original sharp zoning has been softened by heat. Surface features: pitted or glassy facet junctions where the stone was heated after cutting. How Gemmologists Test for Heat Treatment Gemmologists employ advanced techniques, such as gemmological microscopy and testing on specialised equipment including Fourier transform infrared spectroscopy (FTIR), to investigate these inclusions and determine the authenticity and treatment status of sapphires and rubies. A skilled gemmologist should be capable of identifying fracture halos using a loupe or microscope. Heat treatment should also be distinguished from other enhancements. Lead glass filling in ruby and the gas bubbles found in synthetic ruby present very differently under magnification, and each carries very different implications for value. Organisations such as the Gemological Institute of America (GIA) publish detailed research on the inclusions associated with heated stones. Why Corundum Treatment Disclosure Matters Recognising heat-expanded crystals and their associated fracture halos is crucial for both assessing gem quality and educating consumers. An unheated ruby or sapphire of fine colour can command a significant premium over a heated stone of similar appearance, so the treatment status directly affects what a buyer should expect to pay. At E.D.R – European Diamond & Gemstone Reports in London, every ruby and sapphire we examine is checked for evidence of heating, and the result is stated clearly on our Loose Gemstones Report. If you own a ruby or sapphire and would like to know whether it has been treated, get in touch with our laboratory. In conclusion, understanding the effects of heat treatment on corundum, along with the implications of crystal expansions and fracture halos, is essential for all professionals in the gemstone industry. By recognising these characteristics, gemmologists can provide valuable insights into the origins and enhancements of sapphires and rubies, empowering consumers to make informed decisions.