Homebrew PCBs

Volkan wrote: 
> 
> Which etcher can be used for tin or nickel etch resist? Is there any
> practical formula for homebrewers?

Maybe its better to use dip coating of LPI resists filling the holes.
You referred an homebrew resist off PVA and dichromate, other is acrylic
resin and benzophenone (same thing used in dry films) an US based ebay
seller had 50 Lb of this chemical to sell recently. 
If you are using real tin electroplating, you may look to Adam Seychell
work with Ammonium Chloride etchant.
Not ammonium based, the only things i know off as tin resist compatible
etchants are us patents  4144119/4378270  and 4632727.