The beginner student is often overwhelmed by the wealth and complexity of information they are confronted with when working from life. As far as it concerns values, or tones, we can tackle this problem simply by understanding how light travels across a form. Because light always travels in straight lines, we can learn to recognise distinct groups of values which we can expect to find on every form lit from a single light source. This is called the classical order of light, a categorisation of value groups which helps us to begin to understand what we see in nature. As we can see in the diagram above, our first priority when attempting to represent a 3D object on a 2D surface is to separate our lights from our shadows. From there we break these groups down further, each successive step adding greater complexity until we have a fully rendered object.
A solid understanding of these categories of light (as it travels across a form) not only ensures the artists work will look 3D but it also gives the artist greater expressive capability, allowing them to be decisive in their choices when creating an artwork. This is demonstrated in this excellent preparatory drawing by Rubens. In it each category is clearly understood, separated and designed. This understanding of what communicates form to our eye allowed Rubens to gain a strong sense of form in even his quickest of studies.
The artist can also use their understanding to make design choices which economise or emphasise different aspects of the subject. Economy of information in an artwork can serve to heighten the information which the artist does choose to include. In other words, what is left out raises the importance of what is kept in. In this academic study by Thomas Eakins we can see how he edits out almost all the information in the lights of the subject, and equally how he minimises the value shifts between many of the subcategories of the darks. Much of the value range of his materials then is preserved to express the dark halftones, which therefore become the subcategory of light in the drawing which is most expressive of the form. This study is an excellent example of the power an understanding of the classical order of light gives you to design your image when working from life, confident that you will not lose three-dimensionality in your drawing or painting.
by Charlie Pickard