Volume 22, Number 10, April - June 2006

Vol. 22 No. 10 - Patricia Calloway Memorial Issue   Patricia Calloway Memorial Issue
  • Welcome to the Patricia Calloway Memorial Issue
  • Some personal reminiscences of Patricia Calloway
  • Characteristic Spectral Features of iron as a gemstone chromophore
  • Diamond cut grading: Unintended consequences and solutions
  • Problems that may be encountered when identifying gemstones in antique jewellery
  • Vulcanite or Gutta-percha: that is the question
  • My other collection
  • Re-surfacing a refractometer prism

(Follow this link for abstracts of past issues)

Characteristic Spectral Features of iron as a gemstone chromophore

G. Pearson
Mt Waverley Victoria

ABSTRACT
The absorption spectra of a number of frequently encountered gem materials that contain iron were determined using digital UV-Visible spectrophotometry. Sonic shared features were repeatedly observed when these were converted into transmission spectra. These similarities qualify as characterisation features that have not been reported previously in the gemmological literature.

Conversely, although it was expected t( confirm the presence of certain spectra, features which have gemmologically long been considered "diagnostic for iron". the transmission spectral data failed to provide this evidence. A partial explanation of this unexpected result is proposed in discussion of the spectral results relating to the variable sensitivity of human vision with wavelength.

Key words: Gemmology, characteristic spectra, iron, chromophore, spectroscopy

Diamond cut grading: Unintended consequences and solutions

Sergey Sivovolenko, Garry Holloway, Dr Yuri Shelementiev and Janak Mistry1

1 These collaborative authors are known as The Cut Group.
In May 2004 they ran the first International Diamond Cut Conference
in Moscow, Russia

ABSTRACT
 Many diamond grading laboratories are placing more emphasis on cut quality or beauty grades in their reports. A lack of uniformity in grading criteria runs a risk of creating confusion and reducing consumer and industry confidence; but these authors fear a worse problem. Grading the beauty of diamond is complex and consequently labs can only grade the least complex and most abundant faceted diamonds. Because the market prefers to produce, sell, and buy diamonds with third party cut quality endorsement, the development of new cuts will be stymied. Much needed innovation and broader choice for consumers will suffer because of labs introducing cut grading into their diamond reports.

Problems that may be encountered when
identifying gemstones in antique jewellery

Ronnie Bauer
Klepner's Melbourne

ABSTRACT
Identifying gemstones and gem materials set in antique jewellery poses many challenges for the gemmologist. In this contribution the author will present practical advice with respect to how to overcome some of these challenges.

Vulcanite or Gutta-percha: that is the question

Grahame Brown
 Albany Creek, Queensland, Australia

ABSTRACT
Vulcanite and gutta-percha are two dark coloured materials that were moulded to produce various items of relatively inexpensive jewellery during the late 19th and early 20th centuries. Much confusion exists in the gemmological literature, and within various levels of the antiques trade, with respect to how, these two quite different materials should be discriminated from each other. In an attempt at simplifying discrimination between these materials, this paper will present brief histories of man's discovery and use of vulcanite and gutta-percha, their chemistry, their properties, and their identifying features. A simple three step testing sequence then will be offered for consideration by fellow gemmologists.

My other collection

Bob Sneyd
Carina, Brisbane, Queensland

ABSTRACT
The collection of postcards, illustrating gemstones and various aspects of gemmology, is a hobby that has been used by this gemmologist both for his own enjoyment and to promote gemmology. The variety of cards that can be collected illustrated from around the world show how this medium once was and still is a very effective way of promoting gemstones and gemmology.

Re-surfacing a refractometer prism

Trevor Linton
Wellington Point Queensland

ABSTRACT
 In this paper, the potential problems associated with repolishing the degraded soft glass surface of refractometer prisms are described. Explanations and remedies are offered for the errors that are induced in refractometer scale readings as a direct consequence of this commonly used repolishing step.