Here's a monochromatic sketch I did last night. It is oil on linen, about 13x16. It used some good ole' Winsor and Newton burnt sienna with a small amount of winsor green (or veridian) to tone down the background underpainting. I really enjoy doing these kind of monochrome studies. It really helps me free up my brushwork and allows me to focus on pure drawing with a brush. They tend to be pretty quick as well, which is an added bonus.