Shading or with other word, rendering is a fundamental drawing skill. When light interacts with objects, it creates shadows on their surfaces. Light and shadow parts together create forms. This is what the viewer perceives through his/her eyes. As an artist it’s important to understand what is happening on the surface of an object in order to be able to reproduce it properly.
Let’s discover how light behaves on the surface of a sphere illuminated by the sun in 45-degree angle from the top left. Also let’s observe what shadows are created on the object and around the object.
The sphere has a curved surface. Curved surfaces behave differently than flat ones. In case of an object bounded by flat surfaces and sharp edges, the shadow side can be easily defined by the edges of that surface. But in case of a sphere, the situation is a bit more complex.
When you render a curved surface, you need to understand where the shadow side of that object starts. Our brain processes three major graphic elements when it understands a form:
- the light side
- the shadow side
- and the cast shadow
When light (sunlight or local light) hits the surface of an object, it creates value changes on the form. Some area will be lighter, some area will be darker. This will help our brain to understand the object. In drawing we just need to place the light and dark areas at the right places. Of course this is not as easy as it sounds. It requires full understanding on how light behaves on different surfaces. And you also need to do plenty of practice.
The light side of an object is the area that is in direct light. The active highlight is the brightest part of the light side. This small part of the surface is in the position which reflects the most light into the viewer’s eyes. The remaining part of the light side is called passive highlight.
The shadow side consists of that side of the object which is not exposed to direct light, plus the surrounding areas that are covered by the object from direct light. The terminator is the line where the light and shadow side meet. The dark surface of the object is called core shadow. Some parts that are still in the shadow side, but closer to the ground are brighter, because of reflected light coming from the ground. The darkest part of the object surface where it meets the ground on the shadow side is called the occlusion shadow. Finally the terminator line is projected to the ground plane and it forms the border of the cast shadow.
More than one light source
Now if you have more than one light source, and you usually do, because smooth surfaces behave like a mirror becoming light sources themselves, the situation is getting more complex. Lights from different directions interact with each other, so the sphere above might look totally different. This can be a challenging topic even for experienced artists, but it’s not impossible to master your shading or rendering skills to this level. You need to observe many different compositions. Don’t just copy them to the paper, try to analyse and understand why they look the way they look.