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We have selected samples from C.I.G. 's comprehensive gem study collection which are difficult to identify. Most pictures were taken with an immersion-scope (methylene iodide); under a common "dry" microscope with dark-field illumination many features shown here may not be visible. A detailed booklet with computer diskette containing over 100 micro-photographs is available from Gemlab Book Services . © 1996 J. W. Kuehn

Description of inclusion features have been provided by Peter G. Read

501Chatham synthetic Ruby

Internal diagnostic features include various forms of flux residue (opaque white globules, mesh-like patterns and tightly arranged white fingerprints); platinum platelets (hexagonal, triangular, rectangular and spiky) which reflect light with a silvery lustre; thick angular platinum crystals; white cloud-like areas (composed of a dense concentration of minute particles); transparent crystals; hammock-shaped and net-like intertwined feathers; and colour zoning.

502Kashan synthetic Ruby.

The Kashan synthetic ruby has been back in the market after many years of absence.

In the early 1960s stones it was possible to identify traces of the seed crystal within the gem. Feather-like structures similar to those seen in synthetic flux-fusion emeralds, and a dot-dash pattern of droplet-like inclusions were often present. These stones sometimes contained inclusions that resembled the marks made when a loaded paint brush is slapped on a wall (the so-called "paint splash" inclusions).

The later 1970s Kashan rubies often contain solidfilled, coarse negative crystals (which contain a granular or sugary material and have a high degree of reflectivity); clusters of parallel, rod-like, solid-filled negative crystals; wispy patterns resembling rain drops ("rain" or "dust" inclusions); and rain-like structures resembling comets.

Silk is rarely present, and then only appears as single, isolated filaments or needles. The presence in a stone of significant quantities of silk is evidence that the ruby is not a Kashan.

Because Kashan rubies contain varying amounts of iron oxide, their S.W. U-V transmission factors overlap those of natural rubies. The colour of most Kashan rubies is reasonably close to that of many Thai rubies, and in comparing the two, it's worth noting that most Kashans show a stronger orange dichroism than Thai rubies.

503Ramaura synthetic Ruby.

These stones are manufactured by JO Crystal Company in California. Inclusions consist of various forms of flux, particularly coarse orange-yellow flux and white flux "fingerprints".

These features, together with colour zoning, "comet tail" inclusions and conically shaped feathers can provide conclusive proof of synthesis. Another identifying hallmark of the Ramaura ruby is the parallel graining or growth lines, also described as the "Scotch in water" or "heat wave" effect.

What may, however, prove to be the main identifying feature of the Ramaura ruby is its fluorescent zoning under L.W. U-V; the manufacturer claims to have introduced a rare-earth dopant to make the stone more easily identifiable when exposed to U-V.

This fluorescent zoning occurs in thin areas just below the surface. It varies from intense to very intense, and has a colour that ranges from distinct sulphur yellow through yellowish orange to a nearly pure orange. Although generally quite thin, these zoned areas also possess a dull; chalky translucent appearance. Unfortunately, some cut stones have been seen that don't possess this tell-tale fluorescence.

505Ruby doublet

506Ruby, natural, Thailand

In Thai rubies, one of the characteristic inclusions consists of a core with rings around it ("Saturn" inclusion) or a fingerprint pattern that either cuts through the core's centre or rests against it. If there are several Saturn inclusions, they all tend to be orientated parallel to each other.

507Ruby, natural, Thailand