Conveying Tonal Value in Visual Art
When using styli that, on contact with a surface, produce definite lines, tonal value can be expressed by use of two factors (Garcia 2003, 56):
- Varying pressure on the stylus tip varies the concentration or density of the pigment at a given point such that it varies how light or dark it is at that point on the surface
- Use of fine movements and other scribbling similar to crayoning with our styli allows the gradual filling up and adjustment of light and dark across a patch of surface, producing gradation
It is important to note that the curvature or lack thereof of the marks you are building up into a blotch of a tonal value via scribbling, and the variability of their degrees of rotation, describe the texture or curvature of the surface of the object being rendered (refer back to Observing Tonal Values) (Garcia 2003, 58). The surface on which the object is being rendered itself contributes to this texture as well.
A minimum of three tonal values contribute to an art piece’s perceived three-dimensionality (Garcia 2003, 58-59):
- Local tonal value, which is the “dominant, overall value of an object, unaffected by shadow or reflections¨ that “[…] relates to an object’s position on the value scale, from light to dark¨ (Garcia 2003, 58). Because this is the value of the object unaffected by reflections other than those it itself requires for its given hue, let alone shadows cast on it by any objects including itself, it concerns how much of the given hue of the object is event present to us to begin with (refer to Defining Tonal Values). We can also as it result call it the intrinsic tonal value or pigmental tonal value.
- Transitional/middle tonal value, which “provide transition between light and dark value shapes¨ that is typically “softly blended¨ (Garcia 2003, 59).
- Shadow tonal value “are the darkest,¨ as they are a result of the relative obscuring or occlusion of light in the rest of the environment or even for itself as affected by the object of the art, or the direction relative to light for the object of the art (i.e., the availability of light for the surface of the object) (Garcia 2003, 58).
Shadow tonal values themselves come in three categories (Ibid):
- Shadow on an object (which I will personally call directional shadow), “caused by the play of light across it, creating shadows on the side further from the light¨ (Ibid). This is the “shadow¨ on the object produced by a relative deprivation of light for its surface to make use of.
- Cast shadows, or shadows that are due to the relative deprivation of light due to an occlusion or obscuring of light by the object to some part or parts of its environment (Ibid). It is shadow from the blocking of light by the object from reaching other surfaces or objects. The cast shadow “[…] may become long and distorted,¨ nonetheless uniquely reflecting the shape of the occluding or obscuring object (Garcia 2003, 59).
- Balance-point shadows comprise of the “small, very dark area just under an object, where it touches […] surface¨ (Garcia 2003, 59).
Finally, there is reflected light which is additional sources of light that lead to more complex gradients for some if not all shadows, allowing for lighter tonal values within blotches of shadow (Ibid). They can also contribute to phenomena such as highlights.
visual_art spectroscopy spectrum_of_light tonal_value directional_shadow cast_shadow balance-point_shadow vectorial_shadow directional_shadow shadow_tonal_value local_tonal_value pigmental_tonal_value intrinsic_tonal_value transitional_tonal_value middle_tonal_value movement motion textures highlight highlights
bibliography
- Capp, Robbie, ed. “Pencil Values.” In Drawing for the Absolute and Utter Beginner, 55–74. New York: Watson-Guptill Publications, 2003.