Hold your finger up and look at it. The side away from the light is darker. That is a FORM shadow. Now put your finger on a piece of white paper. The paper is darker next to the dark side of your finger. That is a CAST shadow. They are handled differently in painting.
For example, it is great to see a form shadow on a person’s nose, but if you’ve ever looked at photos or paintings with harsh shadows cast by that nose on a cheek, you’ll know that the cast shadow, in this case, breaks up the form of the face.
Trust me, it’s rarely necessary to plot out a cast shadow. While you don’t need to calculate a shadow when painting, understanding some of the basic principles can help you to make better shadow shapes.
In linear perspective part I we learned to draw a box in perspective. Lets get jazzy and cast a shadow from that perspective box. If you haven’t mastered linear perspective part I, go back to that or this lesson will be too confusing.
The principles for casting shadows are different depending on where the light is coming from. Side lighting from the sun, for example, must be conceived as parallel lines meaning the rays don’t converge as they do when the light is behind the object being painted.
Of course, with more complex objects, the plotting gets much more complicated . The idea is to learn HOW TO THINK about the basics when casting shadows.
Assignment: To really get the gist of this, use an object to represent the light source, and a straight edge to represent a ray of light. Put a box on a table and bring the straight edge from the light to the box. You will note that where the straight edge can reach the table, there will be light. Where it can’t, there will be shadow. Where it touches the corners of the box (as shown with a line in the video) and then touches the table is where the shadow and light meet.
I was making diagrams for you when I found this video. Thanks to Bunnygrunts’s great explanation, I can get back to painting now and let you listen to her!
Watch the video.