1. ^{{cite book|first=Gerry A.|last= Turner|title=Design Technics: A Handbook of Forty Art Procedures|url=https://books.google.com/books?id=8WlTAAAAMAAJ|year=1951|publisher=Design Publishing Co.|page=10}}
2. ^{{cite book|last=Hodges|first=Elaine R. S. |contribution=Pencil on Coquille Board|title=The Guild Handbook of Scientific Illustration|contribution-url=https://books.google.com/books?id=gD8pWkA6TcwC&pg=PA143|year=2003|publisher=John Wiley & Sons|isbn=978-0-471-36011-7|pages=143–145}}
3. ^{{cite book|author1=Phyllis Wood|author2=Patrick McDonnell|title=Scientific Illustration: A Guide to Biological, Zoological, and Medical Rendering Techniques, Design, Printing, and Display|url=https://books.google.com/books?id=tHzjM4GmPdQC&pg=PA45|year=1994|publisher=John Wiley & Sons|isbn=978-0-471-28525-0|pages=45–46}}