A couple of notes about ferric chloride for etching metal.  It is
generally unpleasant to handle, will etch almost any metal including
stainless steel and will leave indelible brown marks on almost anything
else including skin.  About the only good thing is that is does not
give off unpleasant fumes.

It is not actually an acid but a very powerful oxidising agent.  As it
etches it is converted from ferric chloride (brown) to ferrous chloride
(green).  The etching process can be dramatically speeded by heating
and agitating the solution.

For an even more dramatic etching process try nitric acid at about
20% concentration.  This is also unpleasant (the smell is choking) but
it does not leave brown marks when you spill it.  Just holes.

Jeffrey Borinsky