For the base canvas, I decided to use 22 count evenweave cotton cross stitch fabric. This allowed me to make the same size stitches as for the Heraldic Pouch, but it provided enough stiffness that I didn't need to worry about putting the fabric on a frame.
I ordered every color of plant-dyed embroidery silk available from Pallia, the website of Dr. Katrin Kania, a textile archeologist. This resulted in 19 colors of mulberry silk and 8 colors of French mulberry silk, which is a bit thicker and less twisted (and a bigger pain to work with).
Dr. Kania is an experimental archeologist, so she was intrigued by my idea of artificially aging the silk to see how it fades. She included a little note of encouragement.