In addition to learning about pigments and other additives, I've been experimenting with beating cotton rag- specifically denim found in the "free box" (where students donate/ recycle old clothing here at the Appalachian Center for Craft).
I was warned by Claudia that we have so much soap in our clothes that I didn't need to "wash" the denim, I could simply rinse it a lot before beating it. I was lucky and the suds didn't get too out-of-control. The color is BEAUTIFUL. I still have a ways to go in beating it, so i had to put it on hold for a while.
[Cotton rag shredded on the left and halfway beaten on the right.]