While I wanted you to first understand the makeup of a shadow in broad terms, a friend reminded me that the actual construction of a specific shadow varies depending upon the angle of the light source and of course the horizon and vanishing points of your painting's composition.
Again, I really don't want to get too technical, forcing the member to dust off your old solid geometry book. However, for those inclined to be accurate in all shadow respects, I urge you to try to read this treatise:
http://www.handprint.com/HP/WCL/perspect6.html which is one of the most accurate and detailed instruction I have found to date. And while you might be overwhelmed by terms like "(1) the shadow vanishing point svp and (2) the light vanishing point lvp. Both points lie in the light plane vanishing line (lpvl)." or "The surface plane is horizontal; the spvl is the horizon line. The vertical shadow vanishing point (svp vertical) is at the intersection of the horizon line with a vertical line through lvp."
Yet, to be totally frank, had I not learned these terms as a youngster, and that through years uncounted I constructed my shadows geometrically, I undoubtedly would be challenged to have the patience or to actually remember them while approaching my seventieth year. But, that said, the article has enough visual aids to get each and every point across, and I highly recommend this article as a starting point for those of you who have trouble creating shadows, even while painting or drawing portraits, landscapes and especially a still life.
Let me know what you think.
