Homebrew PCBs

I made my cucl like you with copper and hcl . adding some drug store
hydrogen peroxide 3% on the bottle will help get it strarted .  the data
on some graphs i was looking at said etch is best at 35c about 2,5 molar
cucl  and  a saturated with sodium cloride also in that same bath of
etchant. allows you to use less hcl.    wonder if you can heat the air
you bubble to warm the solution  rather that cool it .  good luck with
your etcher project.