Homebrew PCBs

Note that H2O2 is photo-sensitive, and should be stored in a light-proof
container.  It will break down over time all by itself.

You don't need a *lot* of H2O2 to etch, so a 3% solution is enough if
you use the 2:1 ratio.  The stronger H2O2 can be used a little at a time
to "freshen" the etchant just before you use it.

When I made my etchant, after I used it for circuit boards, I put about
half a pound of solid copper in it (3-4 liters of etchant) and let it
slowly dissolve, which gave me enough CuCl for the next etch.  It took a
while but eventually worked.  Once it's converted to a CuCl etchant, you
can refresh it with plain old air.