[mighty_atomic_c]

I've had some success converting an old printer to do pen plotting, but I haven't tried PCB manufacture yet because Sharpie marker does not do a sufficient, reliable job at working as a mask. I haven't been able to even use it to touch up my own projects!

My experience is mostly with warmed Ferric Chloride as the etchant, so perhaps ymmv with other etchants. However, in my case, glossy photo paper + laserjet transferred with clothes or hair iron (a tedious and awful process) works well, but Sharpie has not been able to help me touching up any areas damaged by the transfer.

If anyone else has a better mask suggestion than Sharpie, I could try out that sort of thing instead.

[StavrosK]

I used an edding marker (I mention the model in another comment) that worked excellently.