I painted a bird shape with varnish, and then etched the block. The solid black in the middle is where the varnish held on, and resisted the caustic soda; the soft gray around the outside is where the block was etched. The white bits within the bird shape are where the varnish didn't resist the caustic soda.
Then I printed the block with a mask over the background.
And then on coloured backgrounds.
