Visual Optics

By Alan Hodgkinson
Gemworld International Inc
1999 ISBN 0-964-17334-4

Alan Hodgkinson writes:

Visual Optics is a method of directly observing the optical properties of a faceted gemstone, set or unset, by holding the stone close to the eye and observing a distinctive light source at any distance. This method of viewing a gemstone causes images to form on the retina. The images are the product of the gem’s optical behavior, and one learns to interpret the images observed in relative terms of refraction, birefringence, dispersion, and dichroism. The strongest absorption bands in the spectrum are also apparent, as is the newly described B:D ratio index devised by Hanneman.

When taken into total account, the method allows the gemologist to do much useful work by way of identification, confirmation of identity, distinction between two or more possible identities, or at least narrow the field of a process of elimination.

The target and attraction of Visual Optics, is to provide gemological identification or information—without the use of instruments. The method is most useful for the experienced gemologist, but gives the student an exhilarating exercise in awareness of the optical phenomena in gemstones. This latter factor is lacking in most gemological optics learning programmes.

The initial instructions are an introduction to the subject, and ideal for those unfamiliar with Visual Optic, and who may have little or no standard gem testing equipment. Later in the book you will learn of new developments that enable the method to achieve greater accuracy, and reach to further gemological limits. A Visual Optics kit is now available at:

Alan Hodgkinson
Whinhurst
Portencross by West Kilbride
Ayrshire KA23 9PZ
Scotland, UK
Tel: 01294 822 358
Email: alan-hodgkinson@easynet.co.uk