Female nude - back. The Grand Masters Technique Project

After much reading and scouring through various sources, I've decided to try and do it for at least one painting. If the first attempt will be encouraging, I will use this technique in my real painting.
So this one here is a picture I found on the internet (in a dubiously "arty" site...) given I wanted specific details: nude female, but with no complex details like limbs, head, face, etc.