Gemological Equipment Refractometers, Spectroscopes, etc.
Gemological Evaluation Equipment
This list represents the basic testing equipment necessary to test and evaluate a gemstone for color, weight, refractive indices, fluorescence, fractures, dichroism, and authenticity.
Long Wave/Short Wave UV Cabinet
Approximatly 1/3 of all diamonds have a tendency to fluoresce when exposed to ultra-violet (UV) light. When diamonds are viewed under a UV light-source, they tend to fluoresce as blue or violet-blue. Natural fluorescence can help a off-colored diamond look like it is a higher grade than it actually does, which is why it is important to identify it.
Ultraviolet (UV) light rays are beyond the spectrum sensitivity of the human eye. Under an artificial ultraviolet light source, many stones fluoresce or give-off light. The intensity and color of the fluorescence will vary with a short or long wavelength of light. This fluorescence is useful in determining the authenticity of stones.
Kassoy - Long Wave/Short Wave Ultraviolet Light and Viewing Cabinet
Gemological Stereo Microscope
A high-quality Gemological Stereo Microscope is probably on of the most expensive pieces of equipment needed to evaluate gemstones. With a good microscope, filters, and refractive index fluid you can identify most gemstones by determining a stone's internal structures and characteristics, optic characteristics, refractive indices, and double refraction.
For general gem examination, a microscope with 10X, 30X, 40X magnification will be necessary. The light-source will be below the gem under a bellows for transparent material, and above for opaque material. Many microscopes have a rotating objective lens for changing magnification.
Kassoy - Gemological Stereo Microscopes
Meiji Techno - Gemological Stereo Microscopes
Microscopestore.com - Gemological Stereo Microscopes
Infrared Reflectance Meter (Jemeter)
A Jemeter is an instrument for measuring the refractive index of faceted gem stones. The Jemeter operates by utilizing Freznels Law by reflecting a laser-like beam of radiation off of a facet. Only the top layers of atoms are scanned by placing the facet directly over the examination disc.
A Jemeter is calibrated to display refractive Indices at the mean sodium D line of 589.3 nm. Jemeters cover the full refractive-index range from 1.450 to 2.999 and do not require contact liquid. Due to the infrared light source, test results may vary with those using other devices.
Test results of the Gemmeter
A spectroscope is used to determine if a gemstone is a natural material or a synthetic material. Spectroscopes generally use high-dispersion diffraction grating film, movable slits, and a photodetector to measure the properties of light within a specific portion of the spectrum.
Each natural and synthetic mineral has a unique spectral "signature" that can be identified when compared to a full spectrum Fraunhofer chart. The level of absorption and/or transmission from a full spectrum light source that passes through the crystal will identify subtle variations in chemical composition.
The 'Raman Imaging Spectrometer' is a sophisticated piece of testing equipment used to identify inclusions, HPHT treated diamonds, emerald fillers, and for fingerprinting rare gems.
A Polariscope is used to evaluate wether a gemstone is single refracting (as is diamond) or double refracting (as is Cubic Zirconia or Moissanite). The Polariscope uses two polarizing filters orientated at right angles to each other with the gemstone sitting between the two. The Polariscope has a built-in light source underneath the bottom filter.
Polariscopes can also be used to separate synthetic amethyst from natural amethyst, or separate jade and chalcedony from glass. A Polariscope can also detect stress in materials and strain within diamonds and other gemstones.
A Refractometer can determine the type of mineral or gem by precisely measuring the stone's refractive index and comparing that number with the inherent refractive index of the mineral.
The RI of singly refractive (isotropic) and doubly refractive (anisotropic) can also be determined. Refractometers can also be used to distinguish anisotropic optically uniaxial and biaxial gemstones and photopositive or photonegative gemstones.
IdealScope H & A Viewer
An "IdealScope" or "H & A Viewer" (below, center) uses a 10x lens with a pink/red reflector positioned in front of the diamond under a central viewing hole, allowing the viewer to see how much of the red/pink light refracts back from the diamond.
The resulting pattern will be a good indicator of faceting proportion and symmetry.
Color Filter (Chelsea Filter)
A Chelsea filter, also referred to as an "emerald filter" or "color filter," is a gemmological dichromatic filter that can help separate some natural gemstones from their synthetic gemstone counterparts. A Chelsea filter absorbs visible light with the exception of long red wavelengths, which are transmitted through the filter causing some minerals to change color.
The color of a gemstone is due to the absorption and transmission of different wavelengths of full-spectrum white light. The "green" of emerald is created from a combination of different wavelengths that can help distinguish a "chromium" colored natural emerald from other types of green gemstones, or emerald imitations/simulants that are colored by elements other than chromium. Natural emerald that is colored by chromium will appear as pink or red in the Chelsea Filter, although some specimens from India may appear slightly green. Transparent blue stones that appear pink or dirty red should also be suspected of enhancement treatments using chromium. Cobalt colored synthetic spinel, aquamarine and topaz, will also appear red with the filter, whereas most sapphire will appear dirty green.
The Chelsea filter was invented in 1934, by a collaboration with students at the Chelsea College of Science and Technology, and researchers at the Gem Testing Laboratory of the London Chamber of Commerce and Industry.
Darkfield Diamond Viewer
A darkfield diamond viewer is a portable "darkfield" 10X loupe for inspecting diamonds and other gemstones. Using darkfield illumination, a gemologist can detect fracture-filled stones by observing the "flash effect". A darkfield diamond viewer is also a helpful device for detecting small inclusions in gemstones.
Kassoy - Chelsea Filter & Darkfield Diamond Viewer
There are two different types of dichroscopes - London and Calcite. The London dichroscope has two Polarizing filters orientated at right angles to each other, so that the light's vibration-plane enters each polarizing filter at right angles, and the two polarizing filters are joined together in the same plan.
A dichroscope also lets you view the different colors of a dichroic piece of rough gemstone. When you look through the scope, you will see any dichroism that a gemstone rough might have.
Master CZ Colored Grading Set, Sarin Colibri & Colorimeter
CZ Master CZ Colored Grading Sets have high color accuracy and are "Hand Graded" against G.I.A. color master diamonds. The set falls within the first half of the color grade and the CZs are from 0.80 to 1.0 carat.
The ADAPT Diamond Grading light box is designed to help jewelers evaluate diamond color, fluorescence, and reveal fracture filled channels and other flaws. The unit has two 6000ĽK fluorescent bulbs for color grading diamonds against master CZ stone sets. It also has 32 400 nanometer ultraviolet LEDs for checking fluorescence, and 6 bright LED lights, to provide intense light to reveal hidden fracture filling or inclusions.
Sarin's Colibri uses mathematical algorithms to calculate diamond color and measure fluorescence while factoring diamond size and shape. The Colibri has a built-in diamond centering device which contributes to the accuracy of the color grading.
Sarin's DC3000 Diamond Colorimeter (aka Gran Colorimeter) is the latest innovation in diamond spectral analysis and will read out in AGS, GIA-GEM, IGI, and HRD grading scales. The DC3000 is used to accurately grade color types (color typing) that comprise five subdivisions in each of the standard D through Z gading scale designations.
Jeweler's Loupes & Hastings Triplets
A Jeweler's Loupe is the most basic instrument used for evaluating gemstones. Jeweler's Loupes are usually 10x magnification and ultr-compact. With a Jeweler's Loupe you can identify a stone's inclusions and imperfections, and evaluate the faceting quality.
Hastings Triplet Magnifiers have a unique three-element design which provides distortion-free and color-correct viewing. The design reduces or eliminates "pin cushion" distortion and chromatic and/or spherical aberations.
Gem Gauges, Calipers & Leveridge Gauges
A four disc pocket gauge helps estimate the size of diamonds and pearls and enables you to measure both round and baguette cut stones. Digital caliper gauges can measure down to three decimal places in millimeters or inches, and can be zeroed out at any setting.
Leveridge Gauges are used to calculate the weight of diamonds, precious gems and pearls wether they are mounted or loose.
Highly accurate digital electronic scales are used to measure gemstones, metals, and finished pieces of jewelry. Jeweler's scales can use weighing units in grams, ounces, and carats.
Specific Gravity Liquids
The two commonly used ways to determine the specific gravity of a gem or mineral is by using heavy liquids or hydrostatic weighing. Specific Gravity (SG), is a measurement of the relative density of a gem or mineral. Relative density is a comparative scale of how tightly the atoms are grouped in a given material.
Using heavy liquids to measure specific gravity starts with several containers of different liquid solutions, each with gradually increasing density. A gem will either sink, float, or rise to the surface depending on its specific gravity in relation to the liquid.
The Specific Gravity measurement helps identify an unknown gem, mineral, or other material and aids in matching the setting size to a gem's weight.
Gem Evaluation Links
Gemological Equipment Suppliers
Gemological Education Links
Bibliography and Reference on Gem & Rock Formation
1. Paul R. Shaffer, Herbert S. Zim, Raymond Perlman, Rocks, Gems and Minerals . Martin's Press
2. UC Berkeley, Pegmatites . ist-socrates.berkeley.edu
3. Merguerian, Geologic Structure - A Primer . people.hofstra.edu
4. Walter Schumann, Gemstones of the World . NAG Press; 2Rev Ed edition