My art friend Rhonda introduced me to these. A watercolor artist named David Castle makes what he calls "elementals", paintings composed of smaller elements. One of those elements are 'fossil' paintings that he makes using a flat stone as a resist. By looking at the photos and reading a few of his posts, we were able to (mostly) figure out how he does them and gave it a try a couple Sundays ago.
After reading a bit further today, I realize that he starts with a few layers of wet paint before he sets the rock down in it. I started mine with just setting the rock down, then dribbling paint and ink over it. In any case, I like the ones I made and plan to keep playing with this cause I love the effect.
The first four are all about 3" square and done with one rock on cheap 90lb watercolor paper. The last one had 3 rocks on it and is about 8" square. It was on 140lb watercolor paper which I sprayed with water before dropping the paint over the rock.
The first one was done with Moon Shadow Mist in Tawny Turquoise. It's gorgeous in person. I bought 4 colors of their spray inks a couple years ago and haven't used them much but will try the other three with more fossils.
The others are mostly Dyelusions inks and Distress Stains. I didn't do any with watercolors like David does them but will give that a try next.
This is an easy an interesting thing to try. All you need is some heavy paper, a few flat-bottomed rocks, and liquid color of some sort - watercolors, inks, fluid acrylics.
Think I'll cut some postcard sized paper and get some started...