The Xehakis Technique Book by Athanosios David Xenakis is such a wonderful reference tool for the constructions of 4-shaft weaving on a rigid heddle loom.
Use three heddles on your rigid heddle loom to create four harness textiles. You can produce twill, overshot, and more!
This is a PDF Download only. The Xehakis Technique Book is out of print.