Gemstones & Pearls/Gemology
Gemologist in a Box
Are flesh-and-bones gemologists dispensable?
Part hardware and part software, Gemchecker is a new system designed to make gem identification a snap for retailers buying colored gems, stores with a repair department, appraisers and small labs. The system is proficient also at differentiating among flux, flame-fusion or hydrothermal synthetic stones, says Kelvin Johnston, who developed it. This is crucial because natural and synthetic gem characteristics overlap.
The system is composed of four main hardware components: Gemchecker Polariscope, Gemchecker Plus, the Gemchecker Dual Light Source Scanner and the Gemchecker Diamond Tester. (Users should already have a personal computer, preferably a Pentium processor with 128 MB of RAM available.)
The Gemchecker Professional version of the software includes a gem identification module, inventory control and valuation and appraisal modules.
Heres a look at each component.
This component, identical to other polariscopes, is used primarily to make initial determinations such as a gems optic figure and whether its singly or doubly refractive. The polariscope consists of two rotating polarizing filters and a diffused light source whose light rays travel through the filters. In cross-polarized position, no light is able to travel through the filters. Singly refractive stones such as glass, diamond and spinel remain dark as the filters are rotated. Doubly refractive stones blink from light to dark as the filter is rotated. (Editors note: Some singly refractive stones show anomalous double refraction and require additional tests to determine refractivity.)
This electronic, battery-powered instrument is designed for gems with flat facets only. The user places a faceted gem on a small platform with a local sensor. (A probe is supplied for gems mounted in jewelry.) The instrument conducts a chopped-frequency infrared beam through the table to measure the gems approximate density. This determines approximate refractive index. The instrument processes this information and displays an LCD read-out that is cross-correlated with a chart pinpointing a range of possible gems. Combined with information about a gems optic character, identification is close to complete. This information is fed into the users computer through the Gemchecker Identification Program.
Gemchecker Dual Light Source Scanner
The scanner, adapted to the Gemchecker Identification software and the valuation and appraisal software, captures images of the gem or jewel. The scanner mode is capable of a 36-bit image with 600 by 1,200 dpi (a measure of optical resolution). The images, which can be saved in a database, constitute important information for identifying a gems dimensions, shape and overall quality.
Using dual light sources, Johnston adds, its possible to fingerprint a gems inclusions.
In combination with the scanner, the system uses an internal filter to help separate different kinds of synthetic gems. Professional Jeweler visited the company for a test using the filter. Natural and hydrothermal and flux synthetic emeralds were scanned, and the resulting images were completely different colors. The filter is used also to test natural and synthetic rubies and sapphires.
Gemologists Still Needed
Gemchecker is an ambitious system using computer software and instrumentation. Its best used by gemologists and other individuals with greater-than-average computer skills.
The system doesnt use microscopy, which will seem odd to most gemologists who use microscopes as their principal identification tool. But with practice, says Johnston, a user with little gemological background probably can learn how to use it as well.
For a small fee, Gemchecker provides an annual update service.
Gemchecker, New York City; (212) 759-1688, fax (212) 826-7019, www.gemchecker.com.
by Robert Weldon, G.G.
Professional Jeweler submitted a transparent light blue gem for testing. The Gemchecker system correctly identified it as topaz. A few minutes later, the information was entered into the computer and a report was generated, complete with top and bottom views and all relevant gemological details.
Photo by Robert Weldon