Why does etching take so long?

[Falcon15]

I'm an electronic hobbiest and I like to etch my own circuit boards. I don't usually heat the Ferric Chloride, but it still doesn't take that long. But for some reason, the other day I was etching a circuit board and nothing happened to it. after about 2 hours, I decided to get some fresh FeCl3 (Ferric Chloride) and heat it, to speed up the process. But it didn't work. so now I have a half-etched circuit board in my garage. Anyone have any tips no how to speed up the etching process?

[nos_slived]

Use a small air pump(from small fish tank) and blow bubbles into the iron(III) chloride, rather than heating it. Same general idea, but the heat can cause chemical changes which blowing bubbles doesn't.