for the Lab and in the Field | |
| Sometimes the simplest design is also the most elegant. Shown at left is just such an instrument designed by gemologist John Koivula for use with the darkfield microscope. I first came across this while visiting Dick Hughes in his lab where I spent a few days studying thin sections obtained on his mine survey in Kenya and Tanzania. While peering into the microscope, I made a distracted inquiry whether there was a polarizing attachement available given that I am used to working with two filters rather than one. Into my hand came this perfect tool. Made of durable, but light metal with rotating lenses, it rests in the well and the entire unit can be removed and put back without taking one's eyes away from the occulars. My own microscope has lenses which must be fiddled with separately to remove. |
 Polariscope for use with darkfield microscope and strain-free glass conoscopes in a variety of sizes. Photo: E. Skalwold |
| A year of inquiries to both men (and not a few machinists) to obtain one of these finally ended in recently aquiring one from John himself. Though this model is no longer made, with some ingenuity and materials at hand, one can construct a similar unit which will fit the well of different microscope models. Also shown are a variety of strain-free glass conoscopes. The tiny ones are very useful for pulling up optic figures from inclusions lying close to the surface as seen in John's images in his PhotoAtlas series and described in detail by him in the April 1993 issue of The Journal of Gemmology. The stoneholder with conoscope was designed by John together with and made by gemologist, and coincidently also a machinist, Harold Oates. Images from under the microscope using crossed polars. | |
 One of my students at work with the spectroscope. Photo: E. Skalwold |
Another elegant instrument is the OPL handheld diffraction spectroscope which comes in two sizes, both of which are indespensible. Here a gemology student is shown using the large OPL Teaching Spectroscope mounted in its stand. She is adjusting the angle of the fiberoptic light for optimal internally reflected light in a flame fusion synthetic ruby cabochon which sits on the rotating stage. Near at hand are the spectrums of ruby and almandine garnet for reference - these are the two which she has narrowed the separation down to, discarding other red gem spectrums such as zircon, selenium glass, "ruby" glass (Au), REE red glass (rare earth 580 doublet), pyrope garnet, spessartite garnet and spinel. |
| The handheld diffraction spectroscope is a powerful tool. As there is no internal numbered scale, success using it is dependant on becoming very adept at spectrum pattern recognition for those materials which have easily discernable diagnostic features. One can quickly identify jadeite, ruby, several garnets and many other gem materials of natural, man-made or treated natures. For the most precise readings, one must go to a desktop prism spectroscope. The one pictured here was custom-built and has a fiber-optic light equipped with incandescent and monochromatic yellow, red, green and blue light, as well as a stage for transmitted light. Inside the ocular is an adjustable reticule for lining up on absorption lines, the values of which are then read off of the micrometer at the back. With this beautiful instrument one can explore even the most subtle spectrums. |
 Desktop spectroscope. Photo: E. Skalwold |
 Read more about this tiny refractometer! Arguably - because some will argue with good reason (my personal first choice is a microscope when available) - along with the loupe, spectroscope and dichroscope, the refractometer is probably the most important piece of equipment in the gemological toolbox.  Read more about dichroscopes! |
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| There are many models and types which all work on the same principal, that of total internal reflection (TIR). They are all expensive, fragile, somewhat bulky (except for the Duplex III) and require hazardous RI liquids to use. For more information, see Refractometer Comparison. | |
 Student lab-bench showing many of the basic tools of the field of gemology. Photo: E. Skalwold | |
Portable Gemological Equipment | |
I am a tool junky - here are some favorite choices.  | |
 In the market |
In a hectic gem market where the heat is over 100, the activity is intense and the pace fast, the tools at hand are a 10x loupe, a good pair of tweezers and a selection of flashlights.... one does the very best one can with what is available. |
Far away are the sorts of instruments found on the lab bench - heavy, bulky or just not suited for travel. But, there are some wonderful portable or improvised tools which, if the need arises, can be easily brought along or drafted from the condiment tray of that day's lunch (be sure to clean out the fish sauce first). There are several sources of fine gemological equipment. There are even many instruments you can economically construct on your own, especially if you familiarize yourself with the techniques developed by Alan Hodgkinson and Dr. William Hanneman. See: Visual Optics & Affordable Gemology |
 Sauce dish works for immersion in a pinch. Photo: E. Skalwold |
 GemPro Portapac Photo: Jeff Wildman. |
As an apprentice to a senior gemologist, now retired, I was introduced to the line of gem testing instruments supplied by Jeff Wildman, inventor of the PortaLab. His company, Gemological Products, carries many essential tools and really shines with its line of portable equipment, including the Portapac (pictured at left), GemPro refractometer (below) and the infinately useful Mega-loupe. GemPro Refractometer Photo: Jeff Wildman. |
| An excellent article entitled "Portable Instruments and Tips on Practical Gemology in the Field" is to be found in GIA's journal, Gems and Gemology, Spring 2002, Vol. 38, No. 1, (back issue available on the GIA website). This article gives very favorable reviews of Gemological Product's PortaPac and Portalab as well as reviews of other instruments favored by the author, Edward W. Boehm. | |
 GEM Instruments PocketLab Photo: E. Skalwold. GEM Instruments once made a small gemological kit which could easily fit in a pocket or purse for travel. Central to it is the Duplex III refractometer shown; compact, accurate and easy to read, agruably one of the best ever made. Also included are a fine loupe, OPL spectroscope, calcite dichroscope, light base with sodium filter, polars with condensing sphere, darkfield well and stone holder |
 Lightbase with darkfield well. Photo: E. Skalwold.  Contents of the GEM Instruments PocketLab. Photo: E. Skalwold. |