My opinion, don't waste your time with Barnbaum's book (on any topic actually). It gives no detail or methodology on masking. If you want to learn about masking without necessarily taking a workshop, Lynn Radeka's kits (which also include information compiled from others such as Mark Jilg and Dennis McNutt) have good explanations and step by step techniques. Howard Bond's articles are also a good source. For selective masking (pencil shading etc) Alan Ross is a great source. There are of course master printers such as John Sexton who teach masking but it's part of their workshops.