Fourier transform infrared spectroscopy (FTIR)
FTIR (Fourier Transform Infrared Spectrometer) is now a mandatory tool in any modern gemological laboratory. It is routinely used for testing some of the most important gems such as diamond, emerald, corundum, alexandrite, jade, amethyst, amber and turquoise.
Where some of the treatments cannot be detected when viewed with a microscope, but the FTIR would give a conclusive result.
Fourier transform spectroscopy is a less intuitive way to obtain the spectra. Rather than shining a monochromatic beam of light at the sample, this technique shines a beam containing many frequencies of light at once, and measures how much of that beam is absorbed by the sample. Next, the beam is modified to contain a different combination of frequencies, giving a second data point. This process is repeated many times. Afterwards, the computer takes all these data and works backwards to infer what the absorption is at each wavelength.
Some of the uses of FTIR Spectroscopy are as follows,
1.Determination of Heat treatment in Sapphires and Ruby Corundums
2.Distinguishing between Diamond and it’s imitations.
3.Distinguishing between Natural & Synthetic Diamond
4.Determination of Zircon state in Metamict or Crystalline
5.Finding out if an Emerald is Natural or Treated.
6.Distinguishing between Natural and Synthetic citrine
7.Tells us if Jade is Polymer coated or Uncoated.
8.Distinguishing between Taaffeite, Serendibite and Sapphirine.
9.Distinguishing between Scapolite and quartz
And many more spectra…
Identify unknown materials
As early as the beginning of the last decade Raman Spectroscopy has become standard procedure in most labs.
Raman spectrometry is a non destructive identification of gem materials, inclusions and even fillers. Raman spectra can also be obtained from mounted gems and thus plays a convenient and accurate role in gem testing. It also plays a vital role in detecting a wide array of materials such as HPHT treated diamonds, treated jade, etc.
We can identify unknown materials from their unique Raman spectral fingerprints and comparing these with known libraries of spectra.
Ideally Raman instrument is used with high spectral resolution across the whole Raman range. It can identify, differentiate and investigate a wider range of materials.
Differentiation of materials
We can determine if materials are the same or different by comparing their spectra. A high spectral resolution system, such as Raman Spectrometer enables us to distinguish even very similar crystal forms (polymorphic) of the same chemical.
Some of the uses of Raman Spectroscopy are as follows,
1.Distinguishing between a diamond and it’s imitations
2.Distinguishing between Amethyst and Iolite
3.Determination of Enstatite
4.Distinguishing between Garnet varieties – Grossular and Spessartite
5.Distinguishing between Polymer coated or uncoated Jade
6.Identification of Zircon in Metamict state or Crystalline state
(UV-Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent (near-UV and near-infrared [NIR]) ranges. The absorption or reflectance in the visible range directly affects the perceived colour of the chemicals involved. In this region of the electromagnetic spectrum, molecules undergo electronic transitions. This technique is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.
The visible absorption spectra are a direct representation of the constituents (impurities, etc) that cause colour and this property is used to come to reliable conclusions.
UV / VIS plays an important role in the distinguishing varieties of Spinels, to find out if its Cobalt Spinel, Iron Spinel or Chromium component Spinel from its spectra. Also helps in finding out the state of Sapphire Corundums in Metamorphic or Magmatic state, and much more.