* Tone and Shape – are two of the 4 elements of drawing. The other two are line and texture.
In this commentary we will discuss the idea of plasticity and how it relates to the concepts of tone and form.
* Elasticity – is the visual push and pull of lights and darks which, when presented in a harmonious entirety, defines the three- dimensional forms of a portrait.
The human eye can discriminate between many more values than the 12 we generally use in a drawing. That means that the artist must “trick” the eye into believing that it is seeing more than is actually on the drawing paper. To this end we must grasphow light behaves and values are perceived.
The trick is to manipulate the eye’s natural tendency towards finality, i.e., towards finishing a drawing even if parts are not actually there. But the eye only does that without protest if the plasticity is harmonious. Only then will the viewer emotionally connect.
The subject of creating harmonious plasticity is broad. In this commentary we limit ourselves to realistic portraiture.
* Tones – are just degrees of darkness and lightness. We generally limit ourselves to twelve discrete values.
To grasp how a form is rendered we need to grasp how light operates and how values enter into this. There are 2 properties of light relevant to drawing:
(1) Light travels in a straight line and bounces off surfaces.
(2) The intensity of light diminishes quickly with distance.
From these properties it follows that:
* As a form turns away from the light source it dims.
* When two planes face the light they will have different values if their distances from the light source are different. For instance, the cheek closest to the light source will have a lighter tone than the one which is farther away.
* The lightest light on a form is the “highlight”. The highlight is always on a plane that is directly facing the light source.
* Most of a portrait’s tone is so-called halftone. That is, anything in-between pure white and pure black. Halftone rendering is at the same time the most enjoyable and the most difficult part of drawing.
* As a form turns completely away from the light source it slowly descends into shadow, towards totally black (i.e., the absence of light). However, there is more to it.
* There is also reflected light from one plane onto another. Remember, light bounces off surfaces but with diminished intensity. So be cautious not to overdo your reflected light.
* There is also the crest of the shadow which is the darkest value on the form. This band of darkness lies between the darkest halftones and the reflected light. This band of darkness is called the Line of Appelle. It is critical to capture its form correctly because it determines the form’s volume.
* As a form turns away from the light, the half-tone plane changes have a soft edge. The quality of this edge is determined by several factors the most critical of which are the amount of plane change, the intensity of light, and the texture of the surface.
* In portrait drawing there are also cast shadows which are hard-edged and very dark and are cast by one form upon another. An example is the shadow that is cast by the nose onto the cheek.
A superb exercise for comprehending the idea of plasticity is to sketch a white Bowling pin. For a more controlled situation you can build yourself a black box with one side open that fully controls the light of one source and blocks out the light of other sources that could disturb the situation.
In closing, the use of the twelve-value scale together with the above tips allows you to create the necessary plasticity for your subjects.
Remi Engels, Ph.D.
http://www.articlesbase.com/visual-art-articles/guidelines-for-pencil-portrait-drawing-tone-and-form-in-relation-to-plasticity-736444.html
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