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Diamond Shape and Cut A diamond’s beauty, rarity and price all depends on the interplay of all the well-known 4 C’s: • Carat • Clarity • Colour • Shape and Cut The Shape and Cut refers to the diamonds shape and cut style – Round, Square, Pear, or Heart for example. Since a round diamond is symmetrical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes and follows specific proportional guidelines. Non-round shapes, also known as “Fancy Shapes”, will have their own guidelines to be considered well-cut. The variety of shapes and cut let you choose your preferred shape and cut that suits your character and personality, which every time you look at your diamond will wake up your personal memories and let you fall in love with it again. Look at our website for most popular Diamond Shapes and Cuts. You can have a PDF to download and print. Diamond Shape & Cut

The July Birthstone, Onyx July isn’t just about rubies; let’s highlight a captivating alternative: Onyx!  Known for its striking black and white bands, this birthstone signifies strength and protection.  Its name originates from the Greek word “onux” meaning “claw, the name was given to the gemstone as its veined appearance was thought to resemble a claw. This gemstone is a variety of chalcedony quartz that has been cherished since antiquity, with ties to ancient Egyptian and Roman civilisations, who believed it could ward off evil spirits.  Fun fact: It is said to enhance self-control and promote emotional balance!  Discover the beauty of this July birthstone with EDR this month.

As we embrace July, let’s celebrate the captivating corundum ruby! Renowned for its rich red hue, this gem symbolises passion, vitality and protection. The name “ruby” comes from the Latin word “ruber,” meaning red. The July birthstone is part of the corundum family, which also includes the stunning sapphire. Table of ContentsWhat Makes the Gem Red?Where Rubies Come FromPigeon Blood: The Colour That Defines ValueTreatments and Imitations to Be Aware OfRuby Symbolism and HistoryBuying a Ruby with Confidence What Makes the Gem Red? Corundum is crystalline aluminium oxide. When traces of chromium replace some of the aluminium in the crystal lattice, the result is red, and only red corundum may be called ruby – every other colour, from blue to pink to yellow, is a sapphire. The dividing line between pink sapphire and the July gem is a matter of saturation and is one of the most debated boundaries in gemmology. With a hardness of 9 on the Mohs scale, it is second only to diamond, making it an excellent choice for rings and bracelets that are worn every day. Chromium also causes many stones to fluoresce red under ultraviolet light, which gives the finest examples their famous inner glow. Where Rubies Come From Rubies are found worldwide, from the breathtaking landscapes of South and Southeast Asia to the renowned deposits in Africa and North America. The Mogok Valley in Myanmar (Burma) has produced the most celebrated stones for centuries, and “Burmese” remains the benchmark against which others are judged. Since the discovery of the Montepuez deposit in 2009, Mozambique has become the world’s most important source by volume, producing stones of excellent colour and clarity. Thailand, Sri Lanka, Vietnam, Madagascar, Tanzania and Greenland also contribute to the market, each with its own subtle characteristics that help laboratories determine origin. Pigeon Blood: The Colour That Defines Value Their value often hinges on colour, with the highly sought-after “pigeon blood” red leading the pack. The term describes a vivid, pure red with a hint of blue and strong red fluorescence, traditionally associated with the finest Burmese material. Stones that are too dark, too orange or too purplish fall away in price quickly. Clarity is judged more leniently than in diamond, as some fine silk (needle-like rutile inclusions) is expected and can even enhance the colour by scattering light. Fine, untreated stones over three carats are extremely rare, and prices per carat climb steeply with size. Treatments and Imitations to Be Aware Of Most rubies on the market have been heated to improve colour and clarity, a stable and accepted treatment that must be disclosed. Our article on identifying heat treatment in corundum explains the tell-tale signs we look for under the microscope. Lead glass filling: heavily fractured material is filled with high-lead-content glass. These stones are fragile and worth a fraction of an untreated gem. Read our guide to lead glass filled ruby. Synthetics: flame-fusion and flux-grown synthetics have been produced since the 1900s. Curved growth lines and gas bubbles often give them away. Imitations: red spinel, garnet and glass have all been passed off as the July gem; the Black Prince’s Ruby in the Imperial State Crown is in fact a spinel. Ruby Symbolism and History Fun fact: throughout history, rubies have been believed to inspire courage and self-confidence! In ancient Sanskrit the stone was called ratnaraj, “king of precious stones,” and Burmese warriors are said to have inserted them under their skin to make themselves invincible in battle. Today it is the gift for a 40th wedding anniversary as well as the July birthstone. For a reliable overview of the gem’s properties and history, the Gemological Institute of America (GIA) maintains an excellent encyclopedia entry. You can also explore July’s lesser-known alternative, onyx, and the rest of the year on our birthstones page. Buying a Ruby with Confidence Because colour, origin and treatment all have such a dramatic effect on price, an independent laboratory report is essential for any significant purchase. At E.D.R – European Diamond & Gemstone Reports in London we identify natural versus synthetic material, detect heating and glass filling, and issue a Loose Gemstones Report you can rely on. Let this glorious July birthstone guide your journey this month at E.D.R, where we celebrate the scientific wonders of gems. Get in touch to have your stone examined, and stay tuned for more on the enchanting world of birthstones!

June’s Birthstone, Moonstone June is one of the rare months with multiple birthstones, and moonstone is easily one of the most enchanting. A member of the feldspar group, it is prized for its display of labradorescence, a soft, billowy light that seems to glow from within. Colours range from colourless to soft hues of grey, peach, green, and blue, with top-quality stones displaying a vivid blue sheen. Named for its moon-like lustre, this gem has captivated for centuries. The ancient Romans associated it with the goddess Diana, while in Indian tradition, it is a sacred stone believed to offer protection. Recognised in gemmological circles since the 18th century, fine moonstone is sourced from Sri Lanka, India, and the USA. While widely available, high-grade specimens with exceptional clarity and a strong sheen remain highly sought after by collectors. Fun fact: Folklore says it can draw lovers together and heighten intuition, no wonder it carries such mystical charm. Ethereal, historic, and full of meaning, moonstone is a dreamy pick for June babies, symbolising emotional balance and inner strength. If you have any questions about this gem, or any other gemstones, then please get in touch today and our expert team will be more than happy to help!

The Birthstone Of June, Alexandrite June is one of the few months with multiple birthstones, and among them is the truly exceptional alexandrite, which is a part of the chrysoberyl family. Although the classic colour change is from green to red or purplish-red, some stones may also exhibit hues such as yellowish-green in daylight, transitioning to brownish-red under incandescent light. First discovered in Russia’s Ural Mountains in the 1830s and named after Tsar Alexander II, it is prized for its rarity, beauty, and unique colour-changing properties. While sources now include Sri Lanka, Brazil, and East Africa, high-quality examples remain extremely scarce. Fun fact: Alexandrite’s green and red hues mirrored the colours of Imperial Russia’s military, which led to it being regarded as a symbol of good fortune and prestige. With its fascinating optical qualities and rich history, alexandrite is a truly distinctive gem for those born in June. If you have any questions or queries about this gem, or another gemstone, then feel free to get in touch and our expert team will be more than happy to help you!

June’s Birthstone, The Pearl June’s birthstone is the pearl, a unique gem born within the shells of molluscs. What sets pearls apart is their organic origin; they are formed from layers of nacre, a substance secreted by molluscs to coat irritants. This process results in a gem that is not only beautiful but also rich in history and rarity, qualities that elevate it to the status of a true gem. Table of ContentsJune’s Birthstone, The PearlHow a Pearl Is FormedNatural, Cultured and Imitation PearlsJudging the Quality of June’s BirthstoneRecord-Breaking Pearls and a Rich HistoryJune’s Other BirthstonesCaring for Pearl Jewellery How a Pearl Is Formed When a foreign particle or parasite lodges inside an oyster or mussel, the animal protects itself by coating the intruder with nacre – thin, overlapping plates of aragonite bound together with an organic protein called conchiolin. Thousands of these microscopic layers build up over months or years, and it is the way light passes through and reflects between them that creates the soft glow, or orient, that no other gem can imitate. Because it is produced by a living creature, June’s birthstone is classed as an organic gem alongside amber, coral and jet. With a hardness of only 2.5 to 4.5 on the Mohs scale, it is also one of the softest gems used in jewellery, which is why it needs gentle care. Natural, Cultured and Imitation Pearls Almost every pearl sold today is cultured: a technician inserts a bead or a piece of mantle tissue into the mollusc to start the process, and the pearl is harvested a few years later. Natural pearls, which form entirely by chance, are now exceptionally rare and command enormous prices at auction. Our article on natural vs cultured pearls explains how X-ray testing separates the two. Akoya: classic round white pearls from Japan and China, 6–9 mm, with the sharpest lustre. South Sea: the largest cultured pearls, up to 20 mm, in white, silver and gold. Tahitian: naturally dark “black” pearls with peacock, aubergine and pistachio overtones. Freshwater: affordable, colourful and often baroque in shape, grown mainly in China. Imitations: glass or plastic beads coated with fish-scale essence; they feel perfectly smooth against a tooth, whereas real nacre feels faintly gritty. Judging the Quality of June’s Birthstone The value of June’s birthstone is assessed on seven factors: size, shape, colour, lustre, surface quality, nacre thickness and, for strands, matching. Lustre is the most important – a top-quality pearl reflects light like a mirror, while a chalky or dull surface indicates thin nacre. Perfectly round pearls are the rarest shape and the most valuable, though drops, buttons and baroques have their own charm and are often better value. Record-Breaking Pearls and a Rich History Did you know? The largest pearl ever recorded, the Giga Pearl, is the world’s largest certified natural blister pearl. Its recorded weight is a staggering 27.65 kg, which is four times larger than the Pearl of Lao Tzu, the second biggest pearl ever recorded. The Giga Pearl is thought to be over 1,000 years old! Pearls have been treasured for at least 4,000 years. Cleopatra is said to have dissolved one in vinegar to win a wager with Mark Antony, Roman law restricted their wear to the ruling classes, and in Tudor England Elizabeth I was painted draped in rope upon rope of them. Their association with purity and innocence made them the traditional gift for brides long before they became June’s birthstone in the modern list published in 1912. June’s Other Birthstones In addition to pearls, June also features alexandrite and moonstone as birthstones, but the pearl remains the primary gem of the month. You can explore the whole year, from January’s garnet to December’s tanzanite, on our birthstones page. Caring for Pearl Jewellery Put pearls on last, after make-up, perfume and hairspray, and wipe them with a soft cloth after wearing. Never use ultrasonic or steam cleaners, and keep them away from household chemicals and acids. Store them flat in a soft pouch, separately from harder gems that can scratch the nacre. Have strands restrung every year or two if worn regularly, with a knot between each pearl. The Gemological Institute of America (GIA) offers further guidance on pearl grading and care. If you have any questions about June’s birthstone, or would like your pearls identified and reported on, then please get in touch and our experienced team will be happy to assist!

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!

Emerald, a prevalent gemstone in today’s market, boasts a rich history that may surprise you. As the most celebrated variety of beryl, this gemstone is represented here by a natural rough beryl crystal and a beautifully cut 1.07 ct Colombian emerald. Table of ContentsWhat Is Emerald?A History Stretching Back to Ancient EgyptWhere the Gem Is Mined TodayHow to Judge QualityWhy Is Emerald the Birthstone for May?Caring for Your Jewellery What Is Emerald? The gem is the green variety of the mineral beryl, a beryllium aluminium silicate that also gives us aquamarine, morganite and heliodor. Its colour comes from traces of chromium and, in some deposits, vanadium. Beryl that is only a pale or yellowish green is usually sold simply as “green beryl”; the name emerald is reserved for stones with a medium to deep, saturated green. It is reasonably hard at 7.5 to 8 on the Mohs scale, but its natural fractures and inclusions, known affectionately as the stone’s jardin (garden), make it more brittle than its hardness suggests. For this reason most stones are clarity enhanced, a subject we cover in detail in our guide to emerald treatments. A History Stretching Back to Ancient Egypt The name “emerald” originates from the Ancient Greek word “smaragdos,” which translates to “green gem.” This stunning stone has captivated people since at least 330 BC. The earliest recorded mines were located in Egypt, specifically in the Zabara foothills and near El Quseir, remaining active from 330 BC until the 1700s. Cleopatra was famously devoted to the gem, and the Egyptian mines later became known as “Cleopatra’s Mines.” In the Mughal courts of India, large crystals were carved with prayers and floral designs, and several of these engraved treasures survive in museum collections today. Where the Gem Is Mined Today While Egypt is often associated with the origins of this gem, these exquisite stones are found in various parts of the world. Notable sources include Madagascar, Pakistan, Russia, Afghanistan, Zimbabwe and even some northern states in the United States. However, the largest and most commercially significant mines today are situated in Zambia, Brazil and Colombia. Colombian stones were first discovered in the late 1500s by Spanish explorers in the Muzo region. They swiftly began to export the unique gemstone to Europe, where it quickly gained popularity due to its strikingly vibrant green hue and impressive clarity. Zambian material, by contrast, tends to be slightly bluish green and is prized for its high clarity, while Brazil supplies a wide range of commercial qualities. How to Judge Quality As with all coloured stones, colour is the most important factor. The ideal is a vivid, slightly bluish green of medium to medium-dark tone. Because inclusions are expected, clarity is judged by eye rather than under magnification, so a stone that is eye-clean with a fine colour is exceptionally valuable. Cut and carat weight follow, with the classic rectangular step cut – the “emerald cut” – designed specifically to protect the stone’s fragile corners. Origin: Colombian stones command a premium, so independent laboratory confirmation matters. Treatment: the level of oiling or resin filling (none, minor, moderate or significant) has a major influence on price. Natural or synthetic: hydrothermal and flux-grown synthetics have been produced since the 1930s and can be convincing without proper testing. Why Is Emerald the Birthstone for May? So, why is this the birthstone for May? The gem embodies renewal and growth, symbolising the essence of springtime – a perfect fit for the birthstone of this blossoming month. It is also the traditional gift for a 20th and 35th wedding anniversary and has long been associated with wisdom, patience and foresight. The Gemological Institute of America (GIA) notes that it has been one of the most desired green gems for more than five millennia. Explore the rest of the year on our birthstones page, including April’s diamond and June’s pearl. Caring for Your Jewellery Because most stones contain fillers, never clean them in an ultrasonic or steam cleaner and keep them away from harsh chemicals and heat. Warm water, mild soap and a soft brush are all you need. Choose protective settings for rings, and have your jewellery checked periodically so that any loose claws are tightened before a stone is lost. Want to learn more about this gem or any other birthstones? Then feel free to get in touch today and the expert E.D.R team will be happy to provide you with their expertise, including a full Loose Gemstones Report confirming origin and treatment.

April’s Birthstone Diamond – A Timeless Gem of Beauty and Strength For those born in April, the diamond is not just a birthstone but a symbol of enduring beauty, strength, and history. It is one of the most iconic and revered gemstones worldwide, known for its incredible brilliance, hardness, and timeless appeal. In this blog, we will delve into the fascinating history of diamonds, why they were chosen as April’s birthstone, and what makes them so special. Table of ContentsApril’s Birthstone Diamond – A Timeless Gem of Beauty and StrengthThe History of Diamonds in JewelleryWhy Is April’s Birthstone Diamond?Diamonds in Colour – A Spectrum of BeautyThe Enduring Legacy of DiamondsApril’s Birthstone Diamonds – A Birthstone That Lasts Forever The History of Diamonds in Jewellery Diamonds have captured the human imagination for over 3,000 years, with their first recorded use in jewellery originating in ancient India. It is believed that diamonds were first regarded as sacred objects, with the ancient Greeks and Romans viewing them as divine, either as tears of gods or fragments of stars. Such beliefs about diamonds as celestial or godly entities added to their mystique and allure. Diamonds were once extremely rare and thus reserved for the wealthy and powerful. Royal families, kings, and queens frequently adorned themselves with diamonds to signify their wealth and strength. This continued reverence for diamonds persisted throughout the centuries, and the gemstones became symbols of power and authority, a status that continues to this day. During the Middle Ages, diamonds were not only worn as symbols of status but were also believed to have protective powers. Knights and warriors often wore diamonds for their supposed ability to bring invincibility and safeguard them in battle. This belief in diamonds’ ability to ward off danger and bring strength is likely why diamonds became linked to April as its birthstone. Their lasting durability and remarkable properties perfectly embody the traits of resilience and everlasting beauty, making them an ideal gem for those born in the month of renewal. Why Is April’s Birthstone Diamond? Diamonds carry deep symbolic meaning and have long been considered one of the most precious gemstones in the world. It’s no surprise that the birthstone diamond was chosen for April, a month that symbolizes renewal and strength. The tradition of birthstones can be traced back to biblical times, with references in the Book of Exodus. In the Bible, the high priest’s breastplate was said to hold twelve stones, each corresponding to a different month of the year. Over time, these stones became associated with the characteristics of the people born in each respective month, and diamonds were chosen for April because of their beauty, rarity, and symbolism of strength and resilience. The diamond’s symbolism of invincibility and power is part of its long history, and ancient cultures believed that wearing a diamond would provide protection, vitality, and courage. As one of the rarest and most valuable gemstones, diamonds also reflect the uniqueness of those born in April, making them a fitting representation of both rarity and strength. Diamonds in Colour – A Spectrum of Beauty While diamonds are most often associated with clear or colourless stones, they can come in a wide variety of colours. Diamonds come in hues ranging from yellow and blue to rare shades of green, pink, and even red. These coloured diamonds, known as “fancy coloured diamonds,” are highly prized and unique, and they form through various natural processes during their formation. For example, blue diamonds get their colour from the presence of boron, while yellow diamonds develop their hue through nitrogen. The rarest of all diamonds, green diamonds, owe their colour to natural radiation exposure. These coloured diamonds are highly sought after by collectors and jewellery lovers for their rarity and beauty. The Enduring Legacy of Diamonds Diamonds are often associated with love and commitment, especially when used in engagement rings. The phrase “A diamond is forever” has become synonymous with eternal love, further solidifying the diamond’s role as a symbol of enduring devotion. Beyond their emotional and symbolic significance, diamonds are also valued for their physical properties. As the hardest natural substance on Earth (with a Mohs hardness score of 10), diamonds are extremely resistant to scratching, although they can still chip if struck on a cleavage plane. Many natural stones also reveal a hidden glow under UV light, as we explain in our article on fluorescence in diamonds. This makes them perfect for jewellery that is meant to last a lifetime. A diamond’s remarkable hardness also allows it to reflect light in ways that create its signature brilliance and “fire,” making it the ultimate symbol of light and enduring beauty. April’s Birthstone Diamonds – A Birthstone That Lasts Forever Whether you are celebrating a birthday in April or simply have an affinity for the brilliance of diamonds, this remarkable gemstone is much more than just a gem, it is a symbol of strength, endurance, and timeless elegance. With a rich history, enduring properties, and unparalleled beauty, diamonds continue to captivate the world, making the birthstone diamond the perfect gem for those born in April. If you’re interested in learning more about your April birthstone diamond, how it is graded against the 4Cs, or how a natural stone is separated from a laboratory-grown diamond, then feel free to get in touch with our expert team today!

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.