Magilabs > Articles > Limitations of Raman spectrometer

While GemmoRaman-532™ is excellent tool for identifying gemology related materials it would be unethical to market it as black magical box without limitations. Of course it does have them. Every analytical instrument ever made has applications where it shines like a star and then some other fields it simply doesn't work.

First of all, we would like to point out this is relatively low cost product for being Raman spectrometer. It is very good for general identification purposes but it should not be directly compared to high end research grade Ramans having ten or twenty times higher figures on their price tag.

Expensive Raman units are never developed for gemological use since big names are not interested to a niche market. At the same time, every expensive Raman unit is almost never developed having a particular field of work in mind, it must be designed to be used for a wide number of applications: organic and inorganic chemistry, quality control, pharmaceutical, metallurgy, environment sciences etc. Basically a big name manufacturer almost never produces a machine for a single use only. This is one of the reasons why Raman units are often very expensive. The typical user does not take 100% advantage of it’s potential, especially from the library point of view. GemmoRaman-532™ and it's software are specifically designed for gemology. GemmoRaman-532™ library spectra were compared to results obtained with a research grade first class confocal MicroRaman table unit, they matched perfectly for gemological use.

We suggest GemmoRaman-532™ as first tool for use in gem lab for identification purposes. However, it should never be the only one! There is no substitute for gemological microscope for studying inclusions, composite stones, signs of artificial treatments and so on. Please, do not think a small box can take place of experienced gemologist for detecting everything related to synthetic and artificially treated gems of 21st century. On the other hand, our industry has become to a point even most experienced gemologist is in urgent need of advanced instruments for making final decisions.

Natural vs. synthetic materials

In general Raman scattering creates a fingerprint spectrum of the bulk material under study. It does not tell whether it is natural or synthetic origin because their major chemical compositions and crystallography are often exactly the same. However, GemmoRaman-532™ is dual purpose spectrometer having also photoluminescence recording capabilities. Photoluminescence reactions are usually related to minor and trace elements in crystal lattice and in many specific cases gives very detailed information for separating synthetic gems from their natural counterparts and detecting various treatments.

Black materials

Raman spectrometer focuses very high intensity laser beam to the sample. Most gems and gemology related materials does not have problems since they are transparent for green light and will not absorb the energy. However, some black or very dark materials may absorb the light and heat up to temperatures where chemical decomposition starts. This may leave a small crater on the surface or if very unlucky shatter the sample. General rule is to be cautious especially for dark and/or organic looking materials.

Fluorescence

Certain gems having high contents of chromium, manganese, uranium or REE (rare earth elements) fluoresces strongly in 532nm green light making Raman fingerprint measurement difficult or impossible. In many cases however, dual purpose GemmoRaman-532™ is capable to identify the material by it's fluorescence pattern. Additionally, photoluminescence reactions are practical for identifying many artificial treatments and with experience gives semi-quantitative estimate of trace elements such as chromium.

Composite stones

Classical example of rookie gemologist mistake is to make an identification based on R.I. measurement from the table of the gem. If one doesn't look more carefully by microscope or loupe it is really easy to miss the fact pavilion has been made of artificial product like glass while crown is natural gem. We guarantee this mistake works with Raman spectrometer too. Never fail to say hello to the stone by looking it carefully at microscope.

Inclusions

Many more pricey Raman instruments are coupled to microscope allowing more careful beam focusing for detecting inclusions in gems, they're called MicroRaman Confocal spectrometers. GemmoRaman-532™ is not designed for that purpose but for easy detection of bulk material. A good microscope alone would cost at least same amount of money than this product.

Glass

Artificial glass is group of amorphous solidified liquids having very vague set of broadened Raman fingerprints and photoluminescence reactions. There is literally thousands of different kind of glass compositions having diverse PL reactions due to color agents used. It is unpractical for trying to build complete reference database for glass substances.

Metals

Most metals are poor Raman scatterers. Some of them such as gold does not scatter at all. Raman spectrometer can not be used for identification of metals in jewelry. This fact has also pros: Gems can be studied without removing them from their setting because metals doesn't interfere with the Raman spectrum.