Edit: after burning through all 400 of my TOS's, I now understand why people don't bother with gemming. 200k in tomes (rough value of the tomes I had from farming) to make...300k in gold, in a couple of hours. I'd have done better to farm gold.
To be fair, it was like 5 total minutes of work but...oy.
Edit: Apparently I actually made a million gold (some gems hadn't sold). The cost of the tomes sinks the good ship gemcrafting though. If I hadn't have had tomes on hand, I wouldn't have made squat.
I'll now explain the math to anyone that has a boatload of tomes on hand and wants to replicate this (since I can't anymore):
THIS APPLIES ONLY TO EMERALDS!
3 flawless squares cost approximately 1500-2000 gold. This means roughly 18k (in mats) per perfect.
1 Perfect costs 30k to craft (plus the tomes, but since you have those, we're not adding in that cost)
3 perfects costs 90k to craft.
1 Radiant Costs 50k to craft.
So...
You put in 18+90+50 to create one Radiant. Radiants sell for 199. They cost you 158 to craft. That's 41k profit, minus 15% = 34,850 per radiant you sell. Sell ten at a time, that's 134,850 per haul.
Feel free to try to do the math for how much you're spending in Tomes of Secret that you could have sold off at like 700 (-15%) on the AH, if you dare.