Star sapphire cabbing orientation

Just cabbed my first star. I was very happy with the result, however, on closer inspection, the star was not centered. The error, after some research now seems obvious, I did not cab perfectly perpendicular to the c-axis. Having selected the rough based on an iridescent sheen just as a "try and see"and having seen the cabbed result, I then eagerly checked my low grade rough (what I threw to one side as worthless bombs some time ago) for a similar sheen. I found a number of stones with a sheen, however, unlike the star that I cabbed, none of them had a visually recognisable crystal structure that would indicate the plane perpendicular to the c-axis. I am considering orienting the stones by "sheen optimisation". What I mean by this is to close one eye, shine a light from behind my head onto the stone and rotate it until the reflected/refracted light shows the strongest sheen. My theory is, when the maximum sheen occurs (even if the surface is not perpendicular to the incident light, the incident light rays will be parrallel to the c axis.In other words, I will be looking pretty close to straight through the c-axis. If there is anyone out there who could "shed some light" on this issue/theory for me before I start churning through my rough in search of stars and proofs and truths that already exist, I would be very appreciative.

You can buy a product called "star refractol" or failing that, coating the stone in pale honey or glucose syrup will often cause the star to appear on the surface and the orientation to be given away.

Thanks Lefty, I'll give it a go and see if it paints a clearer picture for me. I'll see if I can get my hands on some refractol.

Star refractol that is. I see there is a difference and it has a higher RI than the standard stuff. Cheers again Lefty.

Update: Had a crack at the sheen optimisation method on a black star. The rough was highly irregular, and somewhat translucent under strong back-lighting. Had I oriented the stone by the crystal growth outlines, I would have got it wrong by a long way by looking at the finished product. Sheen optimisation worked well for centering, so, I will try the method again to make sure it wasn't a fluke. However, I cabbed with a high dome and ended up with a dot under normal indoor lighting conditions and a faint star under sunlight. Lesson learned, my next black star will be shallow (re-cut for proof will be in order). Making a lot of errors, but learning from each one. I'm starting to chew through the rough, but good use of the lower grade material in my opinion. One other point of interest, I am starting to see that a good cut star will stand out in the rough. I have thousands of piecces of rough and the first one I cabbed had a good star. The next five....not so much or at all. What are the odds of that. Little fellow stood out like a
sore thumb.

Yeah, the stronger the sheen in the rough, the better usually.