Traditional Analytical Methods
An essential and very important aid for the observation of internal features of gemstones. The inclusions of certain minerals or gemstones are very typical for their geographical origin. By using a microscope, heat-treatments and other clarity enhancements can be identified.
A ratio, which indicates the "optical density" of a substance. It is related to the angles of incidence and refraction of light. The refractive index is different for most gem-species.
Specific Gravity (SG) is the ratio of the weight of a substance to the weight of an equal volume of water. Every gem has its own specific gravity and the SG can be used as an additional value in gemstone identification. For this, a hydrostatic balance is used.
An optical instrument used in testing transparent gemstones to distinguish between isotropic and anisotropic materials.
An instrument for detecting pleochroism in a material. It is constructed so that two pleochroic colors, or shades of color, can be detected and compared side by side in a single view.
GRS uses several different 3-digit carat balances (Mettler Toledo auto-calibration carat balances).
Advanced Analytical Methods
FTIR Spectroscopy (Fourier Transform Infrared)
FTIR spectrometers are used to measure absorption in materials within the infrared part of the electromagnetic spectrum. In infrared spectroscopy, IR radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it is transmitted. The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample.
Like a fingerprint, no two unique molecular structures produce the same infrared spectrum. This makes infrared spectrometry very useful for several types of analysis. For example:
- Detect polymers, oils, and resins used for impregnation, e.g., in jadeite, opal, or emerald
- Distinguish certain natural and synthetic gem materials, e.g., emerald
- Opinions on heat treatment on ruby and sapphire
Raman spectroscopy is used to study vibrational, rotational, and other low-frequency modes in gemstones and minerals. It relies on inelastic scattering, or Raman (Raman effect) scattering of monochromatic light, from a laser in the visible, near-infrared, or near-ultraviolet range. The laser light interacts with molecular vibrations, phonons, or other excitations in the system, resulting in the laser photons' energy being shifted up or down.
The energy shift gives information about the vibrational modes in the system. Raman spectrometry is a swift and reliable tool for the identification of minerals and gemstones. Raman spectrometry is used to:
- Identify gem materials or individual parts of a gem or ornamental object
- Identify inclusions
- Identify filling substances, e.g., resins and oils in emerald
Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (excitation by photons), hence the prefix photo-.
The photoluminescence systems are used to:
- Distinguishing between natural and synthetic diamonds
- Identification of diamond treatments
- Identification of minerals
- Identification of gemstone treatments
UV-VIS Spectroscopy (Ultraviolet-Visible)
UV spectrometers are used to measure and record characteristic absorption patterns within the UV radiation range of the gemstone. The UV-VIS spectrometer is used to:
- Investigate the origins of emeralds and sapphires, where stones of certain different origins may produce different absorption characteristics in the UV and visible regions of the spectrum
- Identification aid for minerals
EDXRF Spectrometry (Energy Dispersive X-Ray Fluorescence)
Energy-dispersive X-ray fluorescence spectrometry is used to analyze the chemical composition of a gemstone. A sample is targeted by high-energy X-ray, Inner orbital electrons are ejected by high energy (short-wavelength) X-rays. This removal results in an unstable atom structure leading to electrons from higher orbital’s falling back into the position of the ejected electron. The energy difference between the original and final orbital is released in the form of characteristic X-rays (fluorescence). The energy and number of these characteristic X-rays are transformed into a spectrum. Each peak is characteristic of a chemical element of a particular atom number. The relative concentrations of elements are indicated by the fluorescent X-ray peak intensities. EDXRF is used to distinguish:
- Natural from synthetic gem materials
- The origin of gemstones by indicating the relative concentration of certain elements
LIBS (Laser-Induced Breakdown Spectroscopy)
A short laser pulse is focused on the surface of a gemstone to create a plasma. Emissions from the atoms and ions in the plasma are collected and analyzed by a high-resolution spectrometer. LIBS is used to:
- Test corundum for beryllium treatments and semiquantitative analysis of light elements: Li, Mg and Be in gemstones.
- The potential origin of a gemstone by detecting certain elements
LA-ICP-MS (Laser Ablation-Inductively Coupled Plasma Mass Spectrometry)
In Laser Ablation Inductively Coupled Plasma Mass Spectrometry, the gemstone or mineral is directly analyzed by ablating with a pulsed laser beam. The created aerosols are transported into the core of inductively coupled argon plasma (ICP), which generates a very high temperature. The plasma in ICP-MS is used to generate ions that are then introduced to the mass analyzer. These ions are then separated and collected according to their mass to charge ratios. LA-ICP-MS is used to:
- Analyze the constituents of a gemstone, mineral, or unknown sample. They can be identified and measured, even very light elements.
LA-ICP-MS analyses are carried out in cooperation with Prof. Günther from the laboratory of inorganic chemistry, ETH Zurich, Switzerland.
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