Kashan 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.