In Thai rubies, one of the characteristic inclusions consists of acore with rings around it ("Saturn" inclusion) or a fingerprintpattern that either cuts through the core's centre or rests againstit. If there are several Saturn inclusions, they all tend to beorientated parallel to each other.
Internal diagnostic features include various forms of flux residue(opaque white globules, mesh-like patterns and tightly arranged whitefingerprints); platinum platelets (hexagonal, triangular, rectangularand spiky) which reflect light with a silvery lustre; thick angularplatinum crystals; white cloud-like areas (composed of a denseconcentration of minute particles); transparent crystals;hammock-shaped and net-like intertwined feathers; and colourzoning.
Similar inclusions appear in Chatham synthetic rubies, with theaddition of thin white-appearing needles of platinum (both straightand curved), transparent clusters of colourless hexagonal tabularcrystals, white wispy veils of fine textured flux and white fluxfingerprints.
Some blue Chatham synthetic sapphires luminesce pale green in L.W.U-V and dull green in S.W. U-V (natural blue sapphires are generallyinert).
The Kashan synthetic ruby has been back in the market after manyyears of absence. In the early 1960s stones it was possible toidentify traces of the seed crystal within the gem. Feather-likestructures 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 marksmade when a loaded paint brush is slapped on a wall (the so-called"paint splash" inclusions).
The later 1970s Kashan rubies often contain solidfilled, coarsenegative crystals (which contain a granular or sugary material andhave 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 resemblingcomets. Silk is rarely present, and then only appears as single,isolated filaments or needles. The presence in a stone of significantquantities of silk is evidence that the ruby is not a Kashan. BecauseKashan rubies contain varying amounts of iron oxide, their S.W. U-Vtransmission factors overlap those of natural rubies.
The colour of most Kashan rubies is reasonably close to that ofmany Thai rubies, and in comparing the two, it's worth noting thatmost Kashans show a stronger orange dichroism than Thai rubies.
These stones are manufactured by JO Crystal Company in California.Inclusions consist of various forms of flux, particularly coarseorange yellow flux and white flux "fingerprints". These features,together with colour zoning, "comet tail" inclusions and conicallyshaped feathers can provide conclusive proof of synthesis.
Another identifying hallmark of the Ramaura ruby is the parallelgraining or growth lines, also described as the "Scotch in water" or"heat wave" effect. What may, however, prove to be the mainidentifying feature of the Ramaura ruby is its fluorescent zoningunder L.W. U-V; the manufacturer claims to have introduced a rareearth dopant to make the stone more easily identifiable when exposedto U-V. This fluorescent zoning occurs in thin areas just below thesurface. It varies from intense to very intense, and has a colourthat ranges from distinct sulphur yellow through yellowish orange toa nearly pure orange. Although generally quite thin, these zonedareas also possess a dull; chalky translucent appearance.
Unfortunately, some cut stones have been seen that don't possessthis tell-tale fluorescence.
Developed by Prof. P.O. Knischka, this synthetic ruby isrecognizable in the rough crystal by its spindleshaped,multi-facetted shape. Facetted stones (these aren't yet widelydistributed) may contain phantom-like clouds of dust particles(similar to those seen in Burma rubies).
Other more diagnostic internal features include swirls of colour;irregularly shaped, net-like liquid feathers; parallel negativecrystals having- the same bipyramidal habit as the host crystal andappearing at the end of long crystal tubes; black, distortedhexagonal platelets of platinum and silver; and two-phase inclusions(with ill-defined void boundaries and conspicuous bubbles), this lastfeature being regarded as an identifying characteristic of Knischkarubies. When visible on a spectroscope, an absorption band between250 and 400 nm is a clear indication that the ruby is a synthetic(this band is more easily detectable on a spectrophotometer).
The Knischka rubies that have been inspected so far show littleiron content, and therefore have a high S.W. U-V transmissionfactor.
This synthetic emerald is grown using the original Linde techniqueand Union Carbide patents. Constants are generally close to those ofthe natural stone, although the S.G. is slightly lower, at 2.68.There's very little iron content, with the result that the stoneshave a high S.W. U-V transmission factor and a strong redfluorescence (even under a beam of high-intensity white light).
Typical inclusions are wedge-shaped, dagger like growth tubes,two-phase features stemming from phenakite crystals, and theoccasional healed-crack type of feature.
Characteristic inclusions include two-phase feathers, nail-likemicroscopic crystals, and elongated flowing growth features. Thestones may also contain small lengths of tubular two-phase inclusions(probably growth tubes).
Developed by M. Lens of France, these synthetic emeralds are grownas rectangular rather than hexagonal crystals and have a tabularhabit. Their constants are slightly lower than those of the naturalstone (R.1.=1.562, 1.566; D.R.= 0.004;
As there's a significant difference between the chemicalcomposition of Gilson opals and natural opals, it's more correct toregard them as simulants rather than synthetic opals. Under U-V(particularly L.W.), the Gilson opals show a distinctive chalkybluish-white body glow and a much stronger surface fluorescence ofthe same colour.
When viewed under highintensity fibre-optic illumination, a"chicken wire" structural effect can be seen. Under normalillumination, the typical "lizard skin" structure present in bothblack and white Gilson opals is also visible. S.G.=2.62-2.65).
Synthetic alexandrite (fluxfusion): First manufactured in theearly 1970s by Creative Crystals Inc. of Danville, Calif., thissynthetic alexandrite has a colour change and characteristicsresembling those of natural stones from Siberia. Typical inclusionsconsist of a layer of dust-like particles parallel to the seedplate,and strong banding or growth lines. Some stones contain groups ofparallel negative crystals. Unlike their natural counterparts, thesestones have a high S.W. U-V transparency factor.
Seiko synthetic alexandrites have a swirled internal structurewhich is characteristic of the floating zone method of synthesis.These alexandrites have Verneuil-type tadpole inclusions (with longtails) and spherical bubbles. The colour change of these stones isreasonable, but not suspiciously good.
Description of inclusion features have been provided by PeterG. Read