I have started etching again after a year long break. I am using the pool acid and hydrogen peroxide etchant, but did the same with the bottle of pre-diluted Ferric Chloride I used a little while back. ANd what I did was to put the board and enough etchant to cover nearly an inch into a disposable plastic food storage bin (Glad or Tupperware). Then I placed the combination in the microwave and ran for 2-3 minutes, until a cooking thermometer registered 120F. By the way, the etchant attacks the thermometer probe, so don't leave it in and rinse it as soon as you are done. I had no trouble with arcing or other common problems of having sheets of conductive metal in the microwave, perhaps because the starter batch had changed to cuperic chloride so that there was lots of copper in the water to diffuse the microwave beams. YMMV.
Even with the hot etchant, I still seem to be seeing 30-45 minutes etch times on 1 oz double sided copper. But much slower if I do not preheat etchant and pcb.
Mike
> need diluting. But heating it does make a big difference. Also, it does not
> seem to work as well as it used to, from my recollection, I used some a
> couple months ago and it took 30 minutes to etch a small board with
> an etchant temp of 100F.