I was looking through the items by Cymon, a friend of mine, and saw that someone had requested the source of the cleaned up briliant cut diamond. I thought it would be a fun exercise to re-create it from scratch and try to make the inside cleaner. I think I have succeeded.

I used information from http://www.jewellerycatalogue.co.uk/diamonds/round-brilliant.htm
to get relevant dimensions and angles. I did my best to get it to look like the images on that page.

I basically started with each section, and cut parts out a little at a time by varying the diameters and heights of the cutouts slightly, in much the manner I imagine someone uses to cut an actual diamond. The bonus being if I cut too much, I could back up and try again.