Patch 2.4.2 just threw the gem market in for a loop. Because Brilliant Glass now has a chance of giving an epic gem, the reagents required for the Jewelcrafting ability became scarce and prices shot through the roof. Uncommon gems which used to rot in players' banks or languish on the Auction Houses started disappearing into the hands of Jewelcrafters and cunning businessmen (sometimes both). Blood Garnets, as nice as they are, never sold for more than 1 Gold apiece, even after Brilliant Glass was introduced. Nowadays, on our server, they're about 10 Gold a pop.
And why not? It's almost impossible to catch it on the Auction Houses now since it's pretty much an instant sale. Even prospecting has gotten some love because even destroying Fel Iron Ore has become useful for a chance to get some uncommon (and sometimes rare) gems. The chain reaction of profit continues as Jewelcrafters prospect, get uncommon gems, create Brilliant Glass, and sometimes luck out on an epic gem. The irony is, with most servers now having the alchemy lab on the Isle of Quel'danas now open for business, epic gems are starting to find their way into the market, driving prices down.
Crimson Spinels, which many guilds rarely put on sale, used to run as high as 800 to 1,000 Gold on our server. Now they have become among the most commonly bought (for badges) and sold (on the AH) gems, averaging about 300 to 400 Gold. Uncommon gems are now bought as a reagent for Brilliant Glass and almost never cut, driving prices up; while epic gems are becoming more and more available, driving prices down. If you're a Jewelcrafter, don't pass up on the chance to Brilliant Glass every 20 hours! It's a crazy time for Jewelcrafting, but it's never been more fun... or profitable.