Cheers Andrew.
I've got a dark one on the dop now and I don't want to count my chickens yet because it's not finished - but things look good so far. This stone as a piece of rough would have completely failed a white paper test - being black unless strongly backlit - but appears otherwise flawless.
It was long and flattish so I cut an extremely simple baguette with only four big facets on the pavilion as reflectors, cut in at 38 degress. Not sure of the exact L/W ratio but it's a pretty long rectangle. I was pleasantly surprised after polishing when I inspected it - even though where the crown will go was still completely covered in dark grey epoxy blocking any light, the stone lit up quite nicely without being backlit, glowing like a red hot coal.
As near as I can discern, the effect seems to be coming from the long keel - the light appears to be easily entering the lower part of the long blade-shaped pavilion from the side (since it can't possibly be coming in through the top yet) and actually reflecting upward into the crown area. I'm going to cut a simple, low-angled step crown and see what happens.
If you see a dark garnet that has a thin wedge, you'll see how easily visible it is to see through that part even if the rest of the stone is practically black.
I remembered ktmman posting an image of faceted garnets he had found at Proston and in the photo they glowed quite nicely. I couldn't see the side profile but they were cut in an emerald fashion.
Anyway, here's hoping this might actually turn out ok.
