Wonderful piece, and I admire your use of non-traditional materials. It reminds me of a close friend who did the same thing. He didn't use coffee, but he did use beef blood (which turns a wonderful sepia tone when it dries.) He also used blueberries, strawberries, goldenrod, turmeric, beets and a number of other natural materials to create his watercolour/ink washes (mixed in solution with gum arabic to make it stick). When I asked him why he didn't use regular materials he said he used to, but one day he was out of a particular colour and the art store was closed, and the grocery stores rarely closed. I thought it sounded good to me.