Using a very long piece of black gessoed canvas board (not sure how I ended up with that, but it was in the pile of boards I keep in the corner).
First, I put down the gesso juice mixture (white gesso, acrylic medium, water) over the black and pressed a stencil over it, creating the stones. Then I used a small plastic "brush" tool and wiped across the top. So it's looking like sea and stones to me right now.
I am letting it sit and dry.
I like this start - now what? Perhaps a little glazing of color?