One witness advised they also compare the ink on the suspect ballots; an easy test and would be very compelling in these regards.
A black felt-tip pen would sink at least somewhat, into paper.
I am not yet certain, re generations of laser printers -— there are by now, many, but I would think that only a special-purpose laser printer cartridge’s “ink” would penetrate - but to a lesser extent.
Meaning, I’m not sure how well you can forge depth, with a laser printer.
I meant to add, that we do have scanners that can discover both colors -and- depth -and- materials. Such as for detecting counterfeit print currency.