Intro to Modeling

Modeling in painting refers to the process of making things look three-dimensional.  It's a place where intellectual understanding, observational ability, and paint handling skills come together.  As such, a large portion of modeling comes down to careful observation and years of experience handling paint.  The intellectual side is largely about understanding how light interacts with and reflects from surfaces, and how the eye processes those.  However, there are a few generalized concepts that can be helpful.

The Poster

The poster is a simplification of the value structure of your image into flat colors instead of smooth gradations. Each form is built up of myriad gradations, which can be difficult to comprehend. The poster simplifies these gradations made up of hundreds or thousands of steps of value into a much smaller and more manageable number of steps. How many steps is up to the artist, and can be quite flexible depending on subject matter and the technique being used.

The idea is to ignore the gradations at first and instead focus on the patterns that the gradations are making. Is it a smooth transition from light to dark? Does it get gradually darker most of the way and then suddenly shift more quickly at the end? Does it shift from dark to light and back to dark? How do all these shifts correspond to the contour?

Thinking of what the gradations are doing and putting them down in steps allows us to analyze the progression of values without worrying about the technique of making the smooth gradations. There are all sorts of ways to make the gradations later, but it's important to understand what's happening in them first.

 Example of digital Poster Study by Jason Rainville

Modeling Factors

The concept of modeling factors builds on the idea of the poster. Within an individual form, the artist decides on a certain number of steps to use in the poster, and these steps correspond to the progression of values one sees in chiaroscuro. The exact number of steps depends on the artist on the technique being used. For example, in more naturalistic techniques the artist might use 14 or more modeling factors, but in a more impressionist technique five or six modeling factors might be sufficient.

These six modeling factors are quite efficient at representing forms, and are a good base for realistic paintings:

• Shadow - This is the area that is blocked from the light source by other parts of the same form or other forms.  It includes cast shadows.
• Light - The area of the form generally facing the light.
• Halftone - Between the shadow and light. While the light and shadow together establish the overall mass of the object, the halftone is critical for defining the more precise shape of the object.  The dividing line between the halftone and shadow is sometimes difficult to discern.  Casting a shadow across the halftone with a paintbrush or pencil can help distinguish the border- anything that is lighter than the shadow cast by the brush is still in halftone.
• Highlight - A specular reflection of the light source. This differs from the light in that it usually will not appear where the form is facing the light, but rather in the spot where the light source would reflect if the form were a mirror.
• Reflected Light - Despite its name this area occurs within the shadow.  The areas in shadow may receive small amounts of light reflected off other surfaces.  In a normal situation with one primary light, the reflected light will almost always be darker than the darkest part of the light on the same material, though it often appears lighter than it is due to simultaneous contrast. 
• Depth (or Accent) - These are shadow areas where very little reflected light is reaching.  Depths will more frequently be found in the shadow or cast shadow, but also occur in the light where two forms or subforms overlap each other dramatically.  They're often found where two forms overlap, such as where the feet touch the ground, the neckline and cuffs where clothing is close to the form of the figure, and in crevices like the armpit and the crotch. Depths are quite valuable for showing one form sitting on top of another.

As few as two modeling factors can be used and still be quite effective. For very realistic renderings the artist might choose to divide each of the factors into 2 or more parts.

Note that for certain surface materials and certain situations some of these factors might not appear, or you might choose to leave them out. For example, matte materials may or may not exhibit a highlight. On fuzzy objects such as a tennis ball there will be no highlight. On very shiny or reflective objects some or all of the modeling factors may obscured by reflections. You might choose to leave out a highlight in situations where the technique you are using doesn't allow you to provide enough information to clearly identify the mark as a highlight.