Modern scratchboard originated in the 19th century in Britain and France. As printing methods developed, scratchboard became a popular medium for reproduction because it replaced wood, metal and linoleum engraving.
It allowed for a fine line appearance that could be photographically reduced for reproduction without losing quality. It was most effective and expeditious for use in single-color book and newspaper printing. From the 1930′s to 1950′s, it was one of the preferred techniques for medical, scientific and product illustration.
In more recent years, it has made a comeback as an appealing medium for editorial illustrators of magazines, ads and graphic novels.
This next picture is not Ferrell, but Henry the VIIth.
Process...Process...Process! Start off with thumbnails.
Finish your tight line work.
Color study and Final.
Summer's is making Twain come to life...look at the balance between positive and negative space. Look how Summer is framing Twain with the background.
This is Leonardo Da Vinci. Look how the lines follow form of the figure and the clothes.
Also, when working on your projects make sure you do studies. Get to know your subject matter, and create studies that fit what you need to learn about your focus. What you need in order to be successful may not be what someone else does. In the action of creation it is about you and your relationships with your subject matter.
Summer did an illustration of how Lincoln could have survived Booth's assassination attempt. Notice there are color studies and value studies. He also researched to try to find reference as close his final concept.
Practice this in pen and ink...