This is how I started this painting. I draw on a piece of tracing paper and when I'm happy with the drawing I transfer it to my gessoed board or canvas. I then refine the drawing further and spray it with a fixative. Next, blocked in the background colorsand started building up the grays in the cow photo. I let that dry. Day 2 I added more to the background colors. Because my drawing was dark, I was able to add my first layer of paint on the object in my still life and still see the details underneath. I did a gray underpainting on the cows and an umber painting on the blocks. I painted the marbles white while I redefined their shape.
I'll add more as the painting progresses.