Alan Hodgkinson and Dr. William Hanneman

Visual Optics
&
The Guide to Affordable Gemology

"Don't believe everything you think..."
author unknown.

Throughout my science education I have been fortunate to have many mentors who have encouraged thinking outside the box, whatever the field might be, from a unique bio-chemistry course at Cornell University to marine science on a remote island in the North Atlantic to gemology labs in steamy Bangkok - which by the way is not so divergent a path as it seems when one considers the implications of crystal structure in molecular biology and bio-mineralization in all it's various forms.

Not least among these teachers has been Alan Hodgkinson, author of Visual Optics, and by extention the writing of his friend and colleague Dr. William Hanneman, SOG (Self-Ordained Gemologist), author of Guide to Affordable Gemology and Naming Gem Garnets.

Charlotte and Alan Hodgkinson and Elise Skalwold.

Alan Hodgkinson and the OPL handheld spectroscope.

Lessons in spectroscopy from Alan Hodgkinson.

Alan re-introduced the art of spectroscopy to me which I had left far behind in my undergraduate studies, thus starting off my formal study of gemology with a great appreciation for the handheld OPL spectroscope and its singular importance to this science.

But, it was the impact of viewing the moonlight through his wife Charlotte's ruby held close the eye which opened the door to a whole new line of thinking and kept that door open... each facet produced a tiny ruby spectrum, no need for a spectroscope - quite a magical end to an evening full of revelations!

"The most remarkable gemological instrument I have ever seen is Alan Hodgkinson's eyeball."
Opening line of "Educating the Eyeball - The Hodgkinson Method" by W.W. Hanneman, Ph.D.

Alan's presentation of Visual Optics and hand's-on demonstration of the Hanneman-Hodgkinson Refractometer sparked an interest in what lay beyond the conventional, leading to a search for his and Dr. Hanneman's books and many journal papers, as well as those of other writers. As I have progressed from self-directed gemological studies, through the GG and FGA programs along with my present delve into optical mineralogy and gemological education, this early introduction to Hanneman-Hodgkinson thinking proves to be a great impact on that path... especially given a written nudge here (now for the FGA ...) and there (be sure to try the bright-line technique) over the intervening years. I look forward to Alan's up-coming book, Gem Testing Techniques (please refer to the resources section for a listing of publications and to the Scottish Branch of the Gemmological Association for more information).

Gemstone Characterization via the
"The Hodgkinson Method."
William Hanneman, Ph.D.

"As initially introduced by its originator, Alan Hodgkinson, it was called, and is generally known as, "Visual Optics"—a term I believe has little meaning to this present generation. Different “versions” of this approach have appeared under such names as "The Eye and Prism Method" or "Visual Gemology (VG)." However, the term "Hodgkinson Method" is specific in that it invokes the specific technique or procedure, as described and developed by Hodgkinson and Hanneman.

To practice the Hodgkinson Method, one holds the table of a faceted gemstone (a round brilliant cut is ideal for learning) as close to one’s eye as possible and observes the appearance of a distant light source. One’s eye sees a circle or partial circle of images of that light source which is formed by light transmitted through individual facets. If the gemstone is birefringent, each image may consist of two images, overlapping or not to some degree.

Elise and Dr. Seriwat captured by Saran's cellphone camera.

Hanneman SG balance
Constructed by Dr. Seriwat Saminpanya
GIT FGA Program, Bangkok

Many early gemologists had already noted this and had used it as a test for double refraction. Others had noted each image, due to dispersion, was spread out to form small spectra. In some cases, one could occasionally observe absorption bands which could be diagnostic. As he explained it to me in 1976, Alan said. "You appreciate that the eye can assess reflection, refraction, and dispersion. The only drawback is that the eye does not actually measure, though it can compare quite accurately."

With my basic understanding of the laws of optics, upon seeing a demonstration of how this technique incorporated them, I was immediately converted. From that point on, I lost a great deal of interest in "gemology by rote," which was and still is the staple of gemological training. I considered learning The Hodgkinson Method both a postgraduate course in gemology as well as an exercise in pattern recognition which could be utilized by those with little training. It does, however, require a bit of intelligence, basic gemological knowledge and desire.

The major contributions of Hodgkinson were two—recognition the diameter of the circle of images was a function of both the refractive index and the pavilion angle of the of the gemstone, and the courage to go out and teach this technique as a useful gemological tool. Initially, this technique was an art, and Alan was the "master artist."

Publication of his ideas in 1979 ("Visual Optics," J. Gemm., 17(5), p. 301-9) elicited a response that this approach did not produce valid results and had not warranted publication. In the words of Hodgkinson, "Visual Optics and its visualiser might have sunk without a trace there and then, but fortunately, the cause was taken up by two stalwart gemmologists, Drs. Jamie Nelson and Bill Hanneman.”" This resulted in the publication of my 1980 article "Educating the Eyeball—The Hodgkinson Method" and my 1982 article "Understanding the Hodgkinson Method." (both available from the author for $2 each, postpaid.).

These articles introduced the concept of the Birefringence:Dispersion Ratio and described the technique and the optical principles on which everything is based. For the next 10 years, Alan promoted this idea in his classes in the UK and I, in the USA, by lecturing at the Tucson Shows.

In the early 1990’s, Alan began coming to the Western Hemisphere to lecture and took over teaching The Hodgkinson Method at Tucson. During this time, the Hanneman-Hodgkinson Refractometer was also developed. This allowed one to convert the visual observations to accurate numerical values of RI, Birefringence, and Dispersion over an unlimited range.

In 1994, Alan met Richard Drucker who subsequently published two editions of Alan’s book, "Visual Optics," and was instrumental in arranging for him a “Grand Nation-wide Lecture Tour” of GIA Alumni Chapters where it was warmly received.

The "Official" approach is described in the two papers of mine which have been previously mentioned, Alan’s two books (which are out of print), and my "Guide to Affordable Gemology." If you are really serious about learning this technique I suggest you avail yourself of this information. All your questions should be answered therein. If not, I shall be happy to oblige, but first, read the articles!

Finally, I believe the Hodgkinson Method should be the first "test" anyone makes before deciding on a course of action to identify any faceted transparent gemstone. It can save much time, trouble, and aggravation. Personally, irrespective of all of one’s academic gemological training and certificates, if one has not mastered the fundamentals of this method, I will never consider that individual a really competent gemologist. (That is not to imply that I am one.)"

(reprinted with permission)
Copyright ©2007 W.W. Hanneman

Click for Detail

Dr. Hanneman and Affordable Gemology

Dr. W. Wm. Hanneman is a retired research analytical chemist with more than 40 years experience with some of this nation's largest corporations. Gemology is his hobby.

In the mid 1960's, desirous of learning gemstone identification, he was told he must first take several prerequisite courses, each of which cost more money. Instead, he decided to buy some good books and teach himself.

As a chemist, and since all gems were chemical compounds, Dr. Hanneman recognized gem identification could be considered a "game" of qualitative analysis. Although having millions of dollors of analytical equipment at his disposal at work, he chose to play this game using the most simple and basic equipment possible. In fact, he made his own equipment.

For 30 years, he has offered some of these simple instruments for sale under the name of Hanneman Geological Instruments to those diligent enough to locate him. Part I of his book (Affordable Gemology) tells how you can make your own instruments.

Along the way, Dr. Hanneman developed and promoted the concept of Confirmative Gemology and his "ultimate weapon," The Jeweler's Eye. After 25 years, The American gemological establishment has yet to come to understand this instrument.

Also, among his creations are an inexpensive specific gravity balance; an unlimited range refractometer; the introduction to gemology of a nontoxic aqueous heavy liquid; the elucidation of the importance of the birefringence : dispersion ratio in confirmative gemology; and Mini-cube designs for spectroscopic, darkfield, and immersion studies. He has also developed several simple inexpensive detectors for the "faux diamond," synthetic moissanite.

Classified as an iconoclast, Dr. Hanneman has found that the American gemological powers have never had an interest in promoting his concepts. Consequently, a whole generation of American gemological graduates has been spawned who do not know his name.

His significant technical papers, have found eager acceptance in foreign journals and his instruments have been featured in the classic English gemological books for nearly 20 years.

In 1975, Dr. Hanneman introduced the Hodgkinson Method to U.S. gemology. Twenty years later, it has now become the "new rage" of the Graduate Gemologists Alumni Groups. This led Dr. Hanneman to remind Alan Hodgkinson that he had been previously warned that promotion by Dr. Hanneman could set the acceptance of any idea back a full generation. It did.

At the 1998 Tucson Gem Show, Dr. Hanneman sought to purchase the latest gem identification textbook from what he considered to be "The Source." He was informed that there was no textbook and their "course material" was the text. Needless to say, to take that course requires an expenditure of several thousand dollars. "So much, for the concept of gem identification for the public," he thought. "Apparently, gemological techniques are destined to become "guild secrets" for only the wealthy. That should not be."

In true iconoclastic form, Dr. Hanneman concluded that his clothes were just as good as the emperor's and he could"
Provide a guide to gemology for those who don't need a diploma to convince themselves or others they can identify gemstones.

Provide a guide to gemology for those who believe they might be interested in learning this subject, but don't want to spend thousands of dollars to find out.

Provide a guide to gemology for present students and past graduates who are interested in being exposed to techniques not covered in their courses.

Provide a guide to viewing gemology from a perspective "foreign" to current views.

Reprinted from Affordable Gemology
Copyright © 2001 W.W. Hanneman, Ph.D.

Back