tbh, i wanted to start with...if you need to ask how to make money with JC, you should pick other proffesion
blue gems are pretty much a waste of time now, unless they are red cuz those still can be sold for decent price. atm best money is in meta gems, but you need a alc transmuter for that (but i recommend that anyway, tons of gold i made with it). So pretty much just buy or mine obsidian/elementium. More low quality gems with obsidium which you need more for meta gems. In Hyjal is pretty easy to mine obsidum today cuz most bots are in Highlands.
anyway, JC alone is not that good money at this moment. In combo with Transmute its a winner.