About sketches...

A sketch (ultimately from Greekσχέδιος –schedios, "done extempore" is a rapidly executed freehanddrawingthat isnot usually intended as a finished work.[4]A sketch may serve a number of purposes: it might record something that the artist sees, it might record or develop an idea for later use or it might be used as a quick way of graphically demonstrating an image, idea or principle.Sketches can be made in any drawing medium. The term is most often applied tographic work executed in a dry media suchassilverpoint,graphite,pencil,charcoalorpastel. But it may also apply to drawings executed in pen and ink, ballpoint pen,water colourandoil paint. The latter two are generally referred to as "water colour sketches" and "oil sketches". A sculptor might model three-dimensional sketches inclay,plasticineor wax.