Here is a wonderful cast drawing done by a student here at the studio. Created from direct observation, it’s an impressive study of a complex set of three dimensional relationships.
Starting such a work is quite a daunting task, yet once one has dealt with the block-in to get correct proportions and they begin to render the volumes the task does become simpler as they progress. At the base of understanding how to render (shade) such a complex set of relationships is the necessity to rationalise the task as an interaction between two givens: the direction of the light and the geometry of the surface in question.
To help with this, students are asked to break down the geometry of what they are seeing into one of the five simple forms: a sphere, cylinder, cone, cuboid/rectangular cuboid, and ovoid (egg) shape. By understanding which of the five simple forms the surface of the object is, we can grasp how to model the light and dark of our medium to create an illusion of a 3D form.
If you are ever having trouble rendering an object, first try to define the surface of the object as an instance of one of the five simple forms. After, follow this simple and never-changing rule: Surfaces that are more perpendicular to the light source are lighter. Those surfaces that turn away from the direction of the light source must be darker in value. Value changes are how we create the eye-tricking appearance of something that has roundness and volume. Simple right? In theory yes, in practice of course, this can be quite challenging for someone that is learning. So often value changes on surfaces are so subtle, that there appears to be hardly and difference from one part to the next.
If you feel at a loss for how to capture the fullness of volume of a surface, it can be quite helpful to see the object up close. Look at it at different angles. Run your finger over the surface to better understand the change in surface orientation. Think sculpturally. Imagine carving away at a form to round it by making it darker on the surface less oriented to the light source.
Of the utmost importance is to think of the big picture. Don’t get lost in details (even when there are lots). There needs to be a strict hierarchy of light and dark which governs the appearance of the object as a whole. Make sure that lights and darks aren’t haphazardly placed (values too light in the shadows and darks too light in the light mass of the form). Good luck!