I have been experimenting with mixing various techniques to create tone for MakerBot Unicorn pen plotting, taking advantage of schmarty's "Unicorn G-Code Extension for Inkscape?" (http://www.thingiverse.com/thing:5986) and dnewman's "Inkscape hatch fill extension." This pigeon will be part of a bookart project I'm working on -- and I will continue to experiment with forms of hatching and crosshatching to give this little drawing tone and dynamics.
The SVG files are Inkscape SVG files and can be opened to manipulate layers -- or simply to print through Marty's script to adjust some of his settings. Or simply take advantage of the Gcode (starts in the very center of the build platform).