【USA】Analytical Techniques in Gemology: A Historical Overview

Gemology has become an increasingly technical field, driven by the need for more advanced analytical methods and instruments to test gem materials (figure 1). This shift reflects the evolving challenges of gem identification, a trend that has been well documented in major gemological journals. This special issue of Gems & Gemology will survey the testing instrumentation currently employed by GIA’s laboratories, reviewing their applications, limitations, and the vital information each technology provides. Important aspects of their use for gem testing will be discussed. Note that equipment developed specifically for the GIA diamond quality grading system or other laboratory activities will not be included. This article opens the Winter 2024 edition by briefly examining the introduction and role of scientific instrumentation in gemology to address identification challenges in the marketplace.

The use of scientific instruments for testing gems at GIA began a few years after its founding in 1931 (figure 2), as reported in early editions of this journal. Prior to that, there were few gem testing instruments designed specifically for jewelers. In the early 1900s, G.F. Herbert Smith at the British Museum in London championed the optical refractometer for gem testing (Herbert Smith, 1907). He and his contemporaries discussed additional practical tests such as dichroism, absorption spectra, density, and hardness. GIA founder Robert M. Shipley sought to expand the development of testing instruments tailored to meet the needs of jewelers and gemologists, while educating them on these tools (figure 3).

In the late 1930s, GIA began evaluating and teaching the proper use of devices such as the loupe, microscope, hand spectroscope, refractometer, and dichroscope. These were produced by various manufacturers, including GIA. Some commercially available scientific instruments were useful for gem studies, but the special needs for holding, manipulating, and illuminating gems often required modifications (such as light source additions to the microscope). Some methods were adopted from the field of mineralogy. By the end of the decade, GIA was the exclusive U.S. distributor for several gemological instruments made abroad and had begun manufacturing its own specialized equipment, including a commercially available stereomicroscope fitted with darkfield illumination, introduced in 1938 (figure 4).

With the establishment of the GIA Gem Trade Laboratory in New York in the fall of 1949, gem testing for trade clients and the use of gemological instruments became more routine at GIA. This use increased with the introduction of the first GIA diamond grading reports in 1955. GIA Gem Instruments was established in 1966 to develop new equipment and refine existing tools. The acquisition of more advanced scientific instrumentation accelerated following the creation of GIA’s research department in 1976. Investment in research staff and analytical instrumentation has continued to the present day, as evidenced by the articles in this special issue.

Instrument development for gem testing often resulted from the need to address new identification challenges in the marketplace when existing instruments and methods were no longer sufficient. The introduction of a new piece of scientific equipment often inspired gem researchers to adapt it for their own needs. In recent decades, the increasing sophistication of gem synthesis and treatment techniques has accelerated the need for more advanced scientific instrumentation.

Modern chemical analysis often involves focusing an electron beam (or some other type of energy) onto a small spot on the mineral’s surface. This causes the elements to emit X-rays at characteristic frequencies, which can be measured by the instrument’s detector. The electron microprobe, introduced in the early 1970s, was often used to obtain quantitative compositional data from rocks and minerals. However, the electron microprobe method required a polished surface for analysis. This surface had to be coated with a thin carbon film to conduct away any buildup of electrical charge, and the element measurement results had to be mathematically corrected to yield accurate composition data (Wilson, 1972; Reed and Ware, 1975; Dunn, 1977; Reed, 1989).