I have been provided with some sapphires from the Frome/Weld River area (NE Tasmania) to cut for an avid prospector. The two I will begin with are quite different in nature. A smaller stone with good clarity and light colour, and a larger, quite dark blue stone, with distinct growth bands visible.
Gee, Tasmanian sapphires when well-coloured can match it with the very best.
This large stone, dopped above, would benefit from being cut as shallow as possible to help lighten it, whilst still considering the critical angle of 34.45°. I think the Jeff Graham Quickie 2 may be a good choice @ 91.2% light return.
Ok – update, having started the pavilion, some cracks that were not visible before cutting, due to the darkness of the stone, are clearly apparent now. This is a typical example of the sorts of challenges that often present themselves during the cutting process.
This has lead to a rethink as to the best cut. The roundish Quickie would now yield unacceptably low, a more rectangular stone would be better so that I can cut the defects off without losing too much stone carat weight.
Changing to a rectangular cushion cut, the Tsunami-311 in fact.
Above are some largish well-formed examples of Tasmanian stones sent to me for cutting a while back. The 4.9 ct sapphire pictured above is a nice example of the dogs-tooth shaped crystal habit.
I examined the sapphire above and tried to determine the best orientation, taking into account inclusions/cracks etc.
I decided that the orientation above would give the cleanest stone with the highest yield – so many factors involved in creating the best final product. A rectangular cushion cut, the Tsunami 311, as per this post was the selection.
Final polish on pavilion (I know I’m really slow, lol)
On to the crown..
Final polish ahead.
Yield was a little lower than I would have hoped at the start, however this is a really clean stone as a result, great colour (and great cut too I must say!)