Wednesday, October 10, 2012

Artist Tip #4 - Understanding Cast Shadows (Part 1)

Shadows can make or break a painting of any representational subject - landscape, still life, or portrait.  Some artists don't hold clearly in their mind the basics of how shadows look and how they best "work" in a painting.  There are two different types of shadows: form shadows and cast shadows.  Form shadows are the lightness or darkness on a 3-dimensional form caused by the uneven lighting received by various areas on that form.  Cast shadows are basically different - they are shadows on one form caused by another form blocking the light.

In this tip, I'll discuss how to handle the value (darkness) of shadows.  In the next tip, I'll explain more, including the direction and style of shadows that I've found work best in my paintings.

Most artists understand that the most important element in any painting is not color or texture, but value.  So if we want our cast shadows to look convincing, we need to understand the value difference on a form between the lit part and the part in shadow.  On an overcast day with weak and diffused lighting, any cast shadow (if there is any at all) will be only slightly darker than the weakly-lit form it is cast upon.  But to give an impression of strong sunlight, there is a rule-of-thumb that I learned from artist Jan Kunz on how dark to make a cast shadow:  the shadow area should be at least 4 values darker than the sunlit surface.  This assumes a value scale of 10 values, grading evenly from white to black.  If you are not familiar with the value scale, you may want to make your own, or purchase one from an art supplier.  I've shown a few value scales above.  Then, by holding the scale next to your painting and squinting, you'll be able to tell the actual value of a particular shape.  Dark shadows can really cause a painting to "pop".

Another important point to keep in mind is that objects already in shadow don't cast an additional shadow.  Since the light on the object has already been blocked, there is no significant light left for the object to block further.  So if you place a figure in shadow, it won't cast an additional shadow, as you can see in the attached painting example.  Painting a shadow-in-shadow is an error that can make a representational painting look rather odd.

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