In the years when home computing was just getting started, Mark experimented with the making of his own shading screens -- usually provided by Letratone and Zip-A-Tone. (For you younger folks, these were plastic sheets with dots printed on them, for the application of mechanical grays. You cut them to the shape you needed, peeled off the back to reveal the adhesive coating, and place them on the drawing.) One of Mark's specialties was the Chain-Mail zip, which you can see in use on the three polar bear ladies above.