Do you struggle with cast shadows in your art? I am often asked where and how big cast shadows should be. I use the scientific method of lighting my subjects with the light coming from 11 o’clock at 45 degrees from the picture plane. I use cast shadows when an object is on top of a surface. Botanical and scientific illustration typically has the subject floating in space. If you are depicting your subject on a surface, a cast shadow will eliminate the appearance of floating. Cast shadows may also appear when one subject is in front of another. A simple example of this is one leaf in front of another leaf. The leaf in the foreground will cast a shadow onto the leaf in the background.
Here is simple diagram of a cube. Notice the grey back wall is casting the shadow onto the surface to produce the shadow. The length of the shadow is determined by the height of the cube and the 45-degree angle from the back left corner.
I recommend placing a piece of tracing paper over your drawings to figure out the angles and lengths of shadows. It can be very frustrating to add a shadow only to change your mind if it doesn’t look right. Erasing mistakes on your final paintings or drawings can often end up ruining hours of hard work. Doing this one intermediate step can help you avoid this pitfall.
If you are interested in learning more about light on form and drawing skills you might consider taking my online distance Foundation Drawing class.