This kind of stone would have actually been better if cut cabachon because it's actually a star ruby . By faceting it you can't see the asterism that you would get if it was cut Cabachon. Which would produce a 6 rayed star
You have to use Diamond because sapphire and Ruby are 9 on the Mohs hardness . Anyhow you can get diamond paste through lots of different lapidary shops in various different grit sizes
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