A friend introduced me to this process. It's the perfect marriage of omni-present environmental botanical natural and 2-D communication. You'll need: watercolor or cotton paper, extra-fine pulverized coffee beans or instant crystalline boiled and dried coffee (instant coffee, Starbucks via), brush, and water. Work as you would with a watercolor or gouache.
Allow for drying time between layers and pay close attention to value. You might want to choose leaf fronds and flora or animal forms. The coffee paste will dry green. Use simple, stylized geometric shape and line to depict emotive expression like the curve of a smile or wide attentive eye.