Dani, In my experience, paint pen will always pit. You can strengthen
it a little by etching your silver for one minute before you add
any resist. This seems to open up the structure of the silver and
give any resist more durability. Clean the silver and pat dry, don't
touch or abrade the etched surface.
If you do a dry toner transfer method, either ironing on an image
that has been laser-printed or photocopied onto acetate, or PnP
Blue, going over it with paint pen will give a strong resist. I iron
on, myself. (For details, check the archive). My very crispest
images are from ironing on an image, then very carefully aligning an
identicle one with the first, and ironing that on.