There are four main stages to an oil painting.  (1)  The first job is to sketch it in pencil (charcoal used in this example so you can see it).  (2)  Then I rough in the main colours using a thin turps wash.  (3)  Stage three is when I paint over the wash using thicker oil paint – this takes the longest as sometimes I need several sessions and I wait for the paint to dry between times.  (4) lastly, I add the final details when the third stage has dried.  I work on several paintings at a time, with the result that it usually takes about six weeks to finish an average size oil painting.