Researchers analyse and come to conclusions about the identity of a sample gem by comparing what they find to a database of the numerous gems GIA has examined over the years. They use their expertise and knowledge to look for the distinctive characteristics that reveal a gem’s identity.
The information they gather and the instruments used to collect it can be categorised into light analysis, atomic structure analysis, chemical analysis and imaging.
LIGHT ANALYSISSpectroscopy analyses the way light interacts with the gem. Researchers can identify a gem, and can often determine if it has been treated or is synthetic, by examining how it absorbs or transmits light.
A visible spectrophotometer shines a narrow beam of light through the gem by scanning through a series of wavelengths, beginning at the blue end of the spectrum and moving through to the red end. Light wavelengths not absorbed by the sample are transmitted to the instrument’s detector (these transmitted portions can be seen by your eye as colour). The results of this analysis are displayed as a graph that shows the relative transmission (or absorption) of light versus wavelength. Researchers use the information to determine the cause of the colour of the material.
The infrared spectrometer measures the invisible light spectrum, known as infrared. Infrared spectra can help the researcher determine if a gem has been treated, or whether it is a type I or type II diamond. This instrument generates radiation at wavelengths beyond the red end of the spectrum where “light” is invisible to the eye but can be felt as heat. These wavelengths can be absorbed, transmitted or reflected by the sample being analysed. Materials such as resin, oil, plastic and other substances used for the treatment of coloured gemstones have distinct features in their infrared spectra and can be detected by the spectrometer.
This special microscope makes it possible for a researcher to create a map of how the infrared spectra change across the surface area of the gem.
The Raman Spectrometer uses a laser to illuminate the sample and record its Raman spectrum that can help researchers identify a gem or mineral specimen. The results, which consist of sharp peaks on a graph, are examined and compared to a known spectrum library of different kinds of gem materials. The instrument can also be used to record emission spectra of samples using a technique called photoluminescence (or PL) spectroscopy (in which the light from the laser causes the sample to emit energy at specific wavelengths to create a luminescence spectrum).
ATOMIC STRUCTURE ANALYSISA gem sample is examined at the atomic level through X-ray diffraction. Researchers use this information to determine its chemical structure and identify the material.
X-ray Diffractometer System
The X-ray diffractor system analyses the crystal structure of a sample by illuminating a powdered sample with a beam of X-rays. The X-ray beam is diffracted, or bent, at specific angles depending upon the atomic structure of the crystal. Researchers compare the results with a standard database of specific angle patterns from known materials. This method destroys a small sample of the gem, but can provide a positive means of identifying the material.
CHEMICAL ANALYSISResearches use chemical analysis to determine what elements a gem is made of and if the gem is natural, synthetic or has been treated.
X-ray Fluorescence (XRF)
X-ray fluorescence helps researchers identify the chemical elements in a gem. By illuminating the sample with energy from an X-ray source, this system records the emission of X-rays of particular energies characteristic of the chemical elements present in the gem. The instrument performs a rapid, nondestructive, qualitative chemical analysis of samples that have a large, flat polished surface. The technique can quickly tell the researcher what chemical elements are present in the sample.
Laser-Ablation, Inductively Coupled Plasma, Mass Spectrometer (LA-ICP-MS)
This advanced instrument helps researchers determine how much of each element is present in the sample. A beam of light from a laser is focused on the surface of a sample and it ablates, or removes, tiny particles from the surface. These particles are moved by a flowing gas into a high-temperature plasma torch where they are broken down so that the individual atoms can be identified by the detector. This makes it possible for the researcher to make a quantitative chemical analysis of the naturally occurring elements, even down to low concentrations in the sample. A very small part of the sample is destroyed in the process.
IMAGINGPhotography, specifically photomicrography, offers researchers a way to capture close-up images of features or inclusions within the gem. Researchers use this information to determine the circumstances around how the gem formed and, for some gems, where it originated.
A binocular photomicroscope is used to capture photographic images of the features, or inclusions, in a gem. Researchers use this information to help identify a gem and determine if it is natural, treated or synthetic.
The DiamondView instrument helps distinguish most natural and synthetic diamonds by using a short-wave ultraviolet source to produce fluorescence patterns. The instrument was developed by researchers from the De Beers Diamond Trading Company in the United Kingdom in 1996.