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Alexandrite or Colour-Shifting Chrysoberyl? Why Lighting Matters

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A gemstone can look different under two lamps without necessarily qualifying as alexandrite. Lighting changes the colours available to illuminate a stone. A narrow-spectrum lamp can therefore create a striking visual shift that needs careful interpretation. What makes alexandrite different? Alexandrite is a variety of chrysoberyl associated with a definite colour change caused by chromium. SSEF’s 2012 news slides compare this with a chrysoberyl that looked different under a particular LED but showed almost no main colour change between daylight and incandescent light. Why the comparison conditions matter A specialised lamp can emphasise only part of a gemstone’s response. The appearance under that lamp is interesting, but it should not replace a comparison under standard lighting conditions. The same caution applies to photographs whose lighting has not been explained. SSEF’s later public article reinforces the need to consider an appropriate colour change together with chromium-rela...
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Radiocarbon Dating of Pearls: What Age Testing Can and Cannot Prove

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Radiocarbon research adds a time-related question to pearl testing: when did the sampled pearl material form? This can help investigate historical claims, but age and natural-versus-cultured formation are different questions. A recent pearl can be either natural or cultured. How the historical research worked SSEF’s 2013 article describes collaboration with ETH Zurich. A small amount of pearl material was removed and measured using accelerator mass spectrometry. The method used carbon-isotope information, including the increase linked to twentieth-century atmospheric nuclear testing. Unlike an X-ray image, this procedure consumes a sample. The article describes an early research project, so its sampling amount and service availability should not be assumed to apply to every current test. Why the environment matters Marine reservoir effects can influence the apparent age. Freshwater pearls may be especially difficult because older carbon from limestone can enter the growing pearl...
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Kashmir Sapphire Identification: Why Velvety Blue Is Not Enough

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Some Kashmir sapphires are famous for a rich blue colour with a soft, velvety appearance. However, other deposits can produce sapphires that look similar. A beautiful visual effect is not enough to establish Kashmir origin. What the laboratory compares SSEF’s 2013 article discusses microscopic growth features, inclusions, chemistry and spectroscopy. Fine particles in some growth zones scatter light and contribute to the characteristic appearance. The shape and arrangement of internal features can provide useful evidence. The article specifically compares Kashmir and Madagascar material. It describes similarities as well as subtle differences and explains why the evidence must be considered together. A single inclusion or one chemical number should not be turned into a universal origin rule. Origin does not guarantee quality Every deposit produces a range of material. SSEF stresses that a Kashmir label does not automatically mean an exceptional stone. Colour, transparency, cut an...
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What Is Odontolite? The Blue Turquoise Lookalike in Antique Jewellery

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Some blue cabochons in antique jewellery may look like turquoise but consist of a different material. Odontolite is one historical example. It is associated with fossil dentine and was also marketed under names such as bone turquoise, which can easily cause confusion. The historic brooch investigation SSEF’s 2012 article describes six brooches containing mostly odontolite, along with some actual turquoise and glass. Microscopic examination and Raman analysis helped separate the materials. The finding shows why matching colour across a jewel does not prove matching identity. How odontolite becomes blue Odontolite contains mainly fluorapatite. The article explains that heating can change the state of manganese traces and create a blue appearance. This is different from simply assuming that every turquoise-coloured material is the mineral turquoise. Surface pores, banding and, in some specimens, features associated with ivory structure contributed to the investigation. Such observa...
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Fancy-Coloured Sapphires: Why Corundum Is Not Always Blue

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Sapphire is often associated with blue, but the corundum family offers a much broader colour range. Yellow, pink, violet and green sapphires are examples of the fancy colours discussed in SSEF’s 2012 Facette. A colourless ideal composition can become colourful through very small changes. What produces the colours? Pure corundum is aluminium oxide. Small amounts of other elements can enter its crystal structure and change which wavelengths it absorbs. Chromium contributes to red ruby colour, while iron and titanium are important in many blue sapphires. The colour depends on more than the total amount of one element. Its chemical state, combinations with other elements and colour centres in the crystal can all matter. Some corundum also shows different colours or shades in different viewing directions, a property called pleochroism. Why colour names have boundaries SSEF discusses the difficulty of separating nearby colour categories, such as pink sapphire and ruby. Variety names i...
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EDXRF Gem Testing: How X-Rays Reveal Chemical Elements

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EDXRF stands for energy-dispersive X-ray fluorescence. It is a laboratory method for examining chemical elements in a gem without drilling a sampling hole. The long name describes a useful principle: elements emit characteristic X-rays when excited. How the measurement works An instrument exposes the sample to X-rays and measures the energies of the X-rays emitted in response. Peaks in the resulting spectrum help identify elements. With suitable calibration, the measurements can also provide information about their amounts. SSEF’s 2011 article explains why this approach is useful for both loose and mounted gems. The article describes the introduction of a particular instrument at that time; it is not a statement about the laboratory’s entire current equipment. What chemistry can help explain Chemical data can support gem identification, colour research and some geographic-origin investigations. It becomes more informative when combined with knowledge of the material and reliable...
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Natural Spinel Colours: Chromium, Iron and Cobalt Explained

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Spinel is more than a red gemstone. Natural examples can be pink, violet, blue and many other shades. Its colour range reflects small differences in chemistry, while its crystal shape and geological setting add further interest for collectors. The role of colour-producing elements SSEF’s 2011 overview describes chemically pure spinel as colourless. Chromium can contribute pink and red, while iron, vanadium and occasionally cobalt influence other colours. The mix and amounts matter, so there is no single colour for all spinel. The article discusses classic and newer sources, including Myanmar, Sri Lanka, Tajikistan, Vietnam, Madagascar and Tanzania. These are historical source examples, not a complete list of every occurrence. Crystal shape is another clue Spinel has a cubic crystal structure and commonly forms octahedra, which resemble two pyramids joined at their bases. Twinning can create interesting shapes. A rough crystal can therefore be attractive even before it is faceted...
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