The background for Brocatello is made from mixing ochre and white, or you can just paint on white and brush the yellow ocher color into it… leaving it darker in patches than other areas.
Then when the background color is dry… put on a thin glaze over it made of raw and burnt sienna with enough glaze to make it rather transparent.
When the color has set sprinkle it over with turpentine by striking a small brush over a stick it will cause it to spread the color and to show the yellow ground through.
Then shade the larger blotches with a light yellow ochre to show the angular fragments and give it depth.
Then vein with color made of vermillion and Prussian blue, being careful not to put in the dark lines through the blotches.