In five or ten minutes, a nice free and loose feel should be apparent in a well executed short sketch. With twenty-minute poses (and longer), the aim is to retain the fluidity of the shorter sketches and use that as an excellent foundation for adding more description.
With this little bit of extra time, you can refine the lines – looking more closely at where the subtle bulges or indentations occur and placing them more carefully.
After a short time focussing on the lines I like to then move onto steady articulation of the quickly mapped-out shadow shapes. Just a bit more care is taken over shading more evenly, especially with longer poses of between 30 minutes and 2 hours. Once the pose is finished (i.e. the model is down) I sometimes spend a few of minutes rubbing (in small circular motions) the shadows and lines with a small (size 4) flat synthetic brush which will add some shine and blending to the drawing.
When I spend 20 minutes or longer on a picture, I like to clean up the outskirts of the sketch with a putty rubber. I do this so that at a later date, when I delve into my archive of sketches and drawings I can clearly see them without too much ‘mud’ fogging them up. Also it is simply good practice to keep your drawings as clean as possible – especially if you are looking to eventually exhibit and sell your artwork.
Here are some other articles on short poses: five minute poses — ten minute poses
