Homebrew PCBs

Hi guys,

I use Ferric Chloride for my etchant, I know there is "neater" stuff 
out there, but this works okay for me - plus I have a couple more 
bags of the stuff to use up.

I have a couple questions regarding useage of it...

1) I don't know why I started doing this, but, before etching a 
board, I stir up all the muck at the bottom of the tank. Then I drop 
in my bubble rock and etch my boards.  Is the mucky stuff at the 
bottom the Ferric Chloride crystals or is it just useless muck?  If 
I don't have to stir it up before use - that would save me a bit of 
messy work.

2) I have lost count of how many boards I have etched with the batch 
I am using right now.  If I were to guess, I would have to say 
probably in the area of 20-25 8" x 10" boards.  Most of those board 
were single sided and all copper removed except for the traces and 
pads.  It currently takes about 20~25 minutes to etch a board with 
the chemicals at around 68 degrees F.  To be honest, I have no idea 
how long it took when I first mixed up the batch :-)  So, I am just 
trying to get a feel for the "Status" of this batch as to whether 
it's time to dump it or keep using it?

3) I know that for some chemical etchants, you use heaters to speed 
up the process.  I recall someone telling me not to use a heater 
with Ferric Chloride so I never did.  However, I did buy a fish tank 
heater, but never used it.  I don't mind waiting 20 minutes to etch 
a board if it is safer than doing it faster with the heater.  If a 
heater is okay to use with this stuff, at what temperature should I 
shoot for? (SAFELY!)

Thanks guys!

Chris