I remember as a kid being fascinated by “invisible”writing techniques, in part because they involved exotic things like lemon juice and candle soot.
I was amazed to find circles and lines drawn on the dunes where the “pen” was invisible. When I looked more closely the “pen,” a small stem of grass or other plant, was, in fact, there but was so insubstantial as to be almost invisible.
To think with the wind they could create such magic! This one was a delightful combination of circular and linear lines.
Still Learning To See 