Corrected transmittance spectrum (non-polarized) of synth. flame fusion ruby as seen in the GLGemSpec interface: For example if transmission for certain wavelengths (in nm) is LOW absorbance for those wavelengths will be HIGH (in a conventional spectroscope one would see dark lines or bands at these positions; indicated as bars and lines).
Noise visible below 350 nm is due to limitations of the halogen light bulb.We improved readability in the 400 nm to 1000 nm range by using a higher voltage (15V) to drive the halogen bulb.
A spectroscope is used to reveal a colored spectrum of a gem by passing artificial light through it. This spectrum is a unique pattern of rainbow-like colors and dark lines or bands for each species of gemstone, so can be used as an identifying criteria.
This large OPL Diffraction Spectroscope comes with a larger eyepiece to allow easier observation of spectrums. The spectroscope is supplied with a Rotating Stand so as to observe spectra easily in loose gemstones, and to provide hands free operation.
The Gem-A Prism Spectroscope is used to test coloured gem materials by observing their absorption spectra. Light is naturally dispersed through a series of prisms, resulting in a wider blue region in this spectroscope, which allows for easy reading of spectra of stones with absorption lines within this range. The adjustable focus sharpens different parts of the spectrum to suit the user's eyesight. Both easy to use and portable.
The spectroscope is a tool for examining which parts of white light are absorbed by a gemstone (as well as by other materials).
Materials can absorb parts of the electromagnetic spectrum, and when the absorbed parts fall within the visible range, that absorbed part will influence the color of the material.
When a gemstone is observed with a spectroscope, the absorbed parts show as dark lines and/or bands in the spectroscope image.
When white light reaches a substance, part of the light components may be absorbed by the substance. The other light components (residue) form the color of that substance. For instance, if a gemstone absorbs all the colors of the rainbow except red, only the red part of the original white light will be visible, and the gemstone will therefore be red.
When viewed through a spectroscope, the absorbed parts of light by that gemstone will disappear from the spectrum image and only red will be visible in the prism of the spectroscope.
Likewise if all colors except red and blue are absorbed by a gemstone, the residual colors (red and blue) will give rise to a purple gemstone.
The diffraction grating spectroscope is based on the principle of diffraction. Maybe the best known brand is OPL, which is produced in the UK by Colin Winter.
Light enters through a narrow slit and is then diffracted by a thin film of diffraction grating material. This produces a linear spectrum image with a generally larger view of the red part than a prism spectroscope.
These spectroscopes do not have a built-in scale.
The prism spectroscope is based on dispersion. The light enters through a narrow slit (some models allow you to adjust the width of the slit) and is then dispersed through a series of prisms. Some models have an attachment with a built-in scale. These models are generally more expensive than their diffraction type cousins.
Because prism spectroscopes are based on dispersion, the blue area of the spectrum is more spread out and the red parts are more condensed than the diffraction grating types.
Using the spectroscope poses many problems for those who are not familiar with the instrument. Therefore, before attempting to determine the absorption spectra of gems, it is best to hold the spectroscope against some different sources of illumination, such as a fluorescent light bulb, a computer monitor, etc. This will show you very clear absorption bands in most cases.
Proper use of the spectroscope and lighting is vital when wanting to see good spectra of gemstones.
The most widely used technique is to make use of reflected light. Light enters the pavilion of a gemstone at a 45ÌŠ angle and the spectroscope should be placed at the same angle on the other side.
The light will travel its longest possible path in this way, picking up the most color.
There are nice spectroscope stands (some with built-in illumination) on the market, but gaining some experience eliminates the need for them.
For the new user, it is recommended to start with a gemstone that produces a clear absorption spectrum, such as synthetic ruby.
What is it?: This handy piece of equipment is perhaps the most important tool in gemology, although GIA students generally get a limited exposure to its use. The spectroscope breaks up the light being transmitted from a gemstone into its spectral colors, which allows the gemologist to see the various wavelengths that are being absorbed by the gemstone. Thereby allowing the gemologist to know what elements are contained in the gemstone that are causing the absorption. Making this one of the most important tools in identifying gemstones.
How does it work?: Elements within a gemstone will absorb certain levels of energy. And light is energy. Therefore certain elements in a gemstone will absorb certain colors of light based on what energy level they are absorbing. The spectroscope allows us to see which color of light, or energy, is being absorbed, thereby allowing us to know what elements are in a gemstone. This, in turn, allows us to know more about the gemstone, ie...identification, where it came from, what causes it to have color, etc....
When you look through a spectroscope you will see lines or bands missing from the colors. This is where elements within the stone have absorbed that level of energy or light, letting us know that the element exists within the stone. Here is an example of the absorption spectrum of zircon:
The wavelengths of light are measured in nanometers. Abbreviated nm. These number are applied to the scale of the spectrum as a guide to show what wavelengths are being absorbed. It should be noted that gemologists should learn to use the spectroscope without having these numbers necessary. Since most hand held spectroscopes will not have these scales visible through the unit. So know where the numbers are, but learn to use your spectroscope without the need to have them visible.
What is the story behind the spectroscope?: There are two types of spectroscope. The prism and the diffraction grating. The prism spectroscope is composed of three optical grade glass prisms in optical contact with each other as shown below, and the diffraction grating spectroscope uses a diffraction plate to break up the light beam. Here is how the two types work:
The prism spectroscope will squeeze the red end of the spectrum making it difficult to see some of the absorption lines in that end. However, the prism models will usually have a focus slide control and a light slit control that allows for adjustments in the amount of light entering the unit.
There are many models of the spectroscope available. From the hand held version as shown at the top of this page which is a hand held diffraction grating model. To the large table top models with lighted scales that you can see through the view hole. Most gemologists should learn with a hand held model without the scale...so you will be able to use it in the field without the need for the big expensive model that you cannot carry.
Spectroscopy has long been used in gemology for the characterization and identification of gems. A spectroscope makes it possible to measure the wavelengths of white light absorbed by the material and thus to deduce information on the chemical nature of the objects measured. When a gem is observed on the spectroscope, the wavelengths absorbed appear in the form of dark bands, more or less fine, superimposed on the image of the spectroscope which is similar to a rainbow (that is, the entire spectrum of visible light).
Different types of spectroscopes exist. They consist of a set of optical components including an entrance slit, a lens and an element capable of separating the wavelengths of light such as a prism or a diffraction grating. Their use consists of positioning the gem under white light and observing with the naked eye the light transmitted (or reflected) by the gem through the spectroscope. It is thus possible to visualize the absorption spectra of the gems, either in transmission or in reflection.
However, this tool has several drawbacks: first, some spectroscopes do not display the wavelength scale (usually graduated in nanometers). The precise position of the characteristic peaks or absorption bands cannot therefore be measured, making the observation inacurate. Moreover, the use with the naked eye of the spectroscope generates in the long run a discomfort and important visual fatigue. Also, the human eye is a very sensitive organ qualitatively but very little effective from a quantitative point of view: it does not allow precise measurement of absorption or transmission at a wavelength of interest, making it impossible to compare certain gems whose differences are sometimes subtle. Finally, the spectroscope does not record a spectrum and the gemologist will have to rely on his memory or a written transcription of what he sees to archive his spectra. Not to mention the impossibility of communicating to others the spectra he visualizes.
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