Bob's scratchboard piece titled "Perennial Asters" is featured in the scratchboard section of book titled "Compendium of Drawing Techniques" by Donna Krizek. The book published in August 2012 is a collection of tips and techniques for many 2-D art mediums. The book is available from Amazon at this link:

http://www.amazon.com/Compendium-Drawing-Techniques-Donna-Krizek/dp/1844488039