I've been experimenting with natural materials-berry juice and feathers. I carved out a feather quill and crushed some poke berries and went at it . This is just on scrap cardboard, and the design is whatever you want it to be (I call it the fiber of life since everything seems to be made of it). The juice shall fade and become brown.
Pokeberries are somewhat toxic... so keep that in mind if ever you decide to experiment with them.
Have you tried experimenting with any other berries? I love the idea of using a natural source for painting, but natural sources can be somewhat hard to work with because the colors fade or change. Would be great to see some more pieces like this.