Microscopy Spectroscopy
AphroDiamante GmbH
Methods of Examination

Interesting news from rapidly developing "diamond science" will be presented here.

To examine gemstones like diamonds there are two main questions to provide answers:

  1. what kind of gemstone (mineral, rock, material) is it,
  2. which peculiarities does it have

The first complex contains the determination of gemstone, the diagnosis. The methods of examination that were developed, base on the determination of the physical and crystallographic properties that are different for each mineral or material. These methods have to get along without any destruction, so that measuring and observation of fissionability, break and hardness can scarcely be used. The choice of the appropriate methods and gadgets is determined by the stone – whether it is rough, cut or manufactured into a setting. One of the eldest methods is the measurement of density (ρ = m/V), usually given in g.cm-3. The different methods are based on the displacement of liquids and therefore require corresponding arrangements with balances.

The optical microscopy, especially polarisation microscopy, allows in combination with further settings the measurement of important optical data, like refraction, double refraction, the optical character, the size of the optical axis angle and several other properties. In addition it can be used to examine inclusions and other inhomogenities.  For the measurement of refraction, double refraction and dispersion of refraction other methods like the various refractor-methods, the measurement of ray deviation or the measurement of reflection ability were developed.

Other optical properties, like for example the colour, are analysed using spectroscopic methods. In this connection the transmission (depends on the wavelength) or rather the absorption of the brought in electromagnetic radiation (not only in the visible part but also in the ultraviolet and the near and middle infrared part of the wavelength’s spectre) are examined. For that, gemmology uses especially UC-VIS-NIR-spectrometers (λ = 200 - 2500 nm) and IR-spectrometers (λ = 1,4 - 25 µm, as reciprocal value: wavelength ν = 1,4 - 25 µm) then often designed as microscope spectrometers. These modern, mainly precise and fast working gadgets are quite expensive and can be cheaper when the frequency spectre is limited. Analog spectrometric arrangements exist for the analysis of the photoluminescence of laser stimulation of discrete wavelengths in a spectre between 200 and 500 nm, the cathodoluminescence and the Raman spectroscopy.

The x-ray diffraction method offers quite unambiguous diagnostic statements, but its appliance is limited by its high apparatus demands. A similar problem exists for the use of electron microscopy or the micro probe.

The second complex of tasks aims at a more detailed statement on the respective gemstone or material, as far as the diagnosis is settled. There are special gemmological or scientific questions, that can be answered in their vast majority with the help of the mentioned examination methods. If gemstones – simulations or imitations – can be diagnostically unambiguously determined, the question whether the stone is natural or synthetically produced requires specific examination.

In this case the determination of characteristic inclusions or growth characteristics can offer answers. Often it has to be decided, whether a natural stone was treated thermically or with radiation.

In this way it can be concluded that there are many simpler and quite large-scale examination methods that can answer nearly all material diagnostic questions and which allow the examination of a bundle of material specific properties and peculiarities. To have all the methodical possibilities in examination and all the gadgets in a single laboratory is hardly possible. That is why it is even for the examination of gemstones of importance to reach a convenient relation between expense and use.

groessenwahn.com - Webdesign aus Berlin