I have used both Ferric Chloride and Sodium Persulfate for etching. The Ferric is very quick, but the Persulfate is gentle and tends to undercut the traces less. My best results have come from Eagle(The best!) with a Laser printer and photo etching using Injectorall boards. I will routinely print .010" width lines with less than .007" spacing. I could never achieve this with iron on personally. As far as the etchant, I will heat Ferric up to 125F in the microwave, in a pyrex dish. I drop the board in, and gently wipe it with a foam paint brush of the desired width. Etching time is around 2-3 minutes for 1 oz copper. Other than fumes and my better half yelling at me for the occasional stain on the microwave handle, I have had no problems. I never heat the solution more than 5 seconds at a time before swirling. I'll put in enough to cover the board + 3/8".

Ron