Hi Michael,

I think it's pretty obvious that he meant etch-resist, but I am making an assumption there.

Bartosz, any ink will act as an etch-resist. The more opaque it is, the more resistant it will be. You can make an Etch Resist Pen by writing "Etch Resist Pen" on a label and applying it to a "Sharpie" by Marks-A-Lot. Nonetheless, you're idea of printing the pattern directly onto the Cu-clad board can be done with an appropriate printer, but only for single sided boards.