Thanks for all the support, everyone! Here's a quick little test just to get a feel for this intaglio idea. Here's a block with a little two-inch "tree" incised into it:
And here's a print taken from the block with full-strength pigment and no wiping - just a scrubbing with the maru bake brush:
That was way too dark, so I tried one with lots of water, still no wiping:
Kind of neat, but awfully subtle. Here's full-strength pigment and just a little wiping. The lines are printing kind of white here:
Here I've wiped more thoroughly:
And here's the ghost (second time printing with no pigment added) from the previous print:
These are down and dirty experiments, but there are definitely some possibilities here, any of which would probably be difficult to get control over. And as Tom mentioned in a previous comment, it's also likely that different inks would behave in different ways. Hmmm. Now to decide if I want to try this on my "Playing With Fire" print.