Defining the Basic Forms with Value
Presented here are the rules that govern how value patterns define the basic forms in their ideal state. It is possible to find on these forms light and shadow shapes that do not fit the rules-shapes created when the light source is at an unusual angle, for example. It is not necessarily wrong to include these "other" shapes in your drawings, but they will not enhance, and may actually confuse, your viewer's recognition of a given form, as well as interfere with the illusion of three-dimensionality.
The Cube
A cube is made up of flat areas called planes. When a cube's plane is parallel to the picture plane, it is depicted as a single tone. A cube in one-point perspective will have its front surface, or plane, depicted as a single tone because the front is parallel to the picture plane. When a cube's plane is not parallel to the picture plane, it is depicted as a blend, a gradual transition from a lighter to a darker value.
Strong contrast between an object and its surroundings (including adjacent forms) makes the object appear to advance; weak contrast between these elements makes the object appear to recede, A cube's plane appears to recede in space when the contrast between its value and that of its surroundings is greatest in the foreground and least in the background. Thus, when drawing a cube's plane against a light background, you would make the blend darkest on the part of the plane that's closest to the foreground so it will seem to advance, and lighten the blend progressively as the plane recedes in space toward the light background.
A cube with no side parallel to the picture plane is made up of various blends. How these blends are arranged will determine whether we are looking at the outside or the inside of the cube. If the light portion of a blend on one plane meets the dark portion of a blend on an adjoining plane, a strong contrast results, creating the impression of an edge that comes forward. Conversely, a low contrast between the values of blends meeting at the Juncture of two planes creates the impression of an inside or receding corner. Imagine an open box. The corner nearest the picture plane is composed of two adjacent planes that contrast more with each other than do the two planes that meet to form the inside far comer of the same box.
Remember these points:
- All flat planes are treated the same as the sides of a cube.
- A clearly defined border between the values of two flat planes implies a sharp edge. As the border between these two values becomes more gradual, or blended, the edge appears rounded; the wider the blend the more rounded the edge. The rounded edge of a cube is actually a portion of a cylinder.
Cubes are made of flat areas called planes. A plane that is parallel to the picture plane is depicted as a single value. A plane that is not parallel to the picture plane is depicted with a blend, a gradual transition from one value to another.
The plane of this wall is parallel to the picture plane of the canvas. It is therefore depicted on the canvas as a single value.
The plane of the cheese is not parallel to the picture plane of the canvas in this illustration. It is therefore depicted on the canvas as a blend from one value to another.
The inside corner of the room appears to recede because where the planes (walls) meet, the blends that describe them are in low contrast. The near corner of the box advances because the blends of its planes meet in high contrast.
The Cylinder
A solid cylinder has a flat top and bottom, which are depicted as fiat planes, just as the sides of a cube are. The curved part of the cylinder is depicted with a blend of values rendered as parallel stripes. As long as values are in parallel stripes, the form described is cylindrical.
Cylindrical forms are described by blends of light to dark parallel stripes. The angle from which you view a cylinder determines the shape of its top; from overhead this shape is a circle, while at other angles it appears to be an ellipse (for more on this, see the chapter on elliptical perspective).
A roll of paper is a cylindrical shape; its light and shadow shapes are blends of parallel stripes. (The loose paper is a cone.)
The Cone
The flat bottom face of a solid cone is a plane and is therefore depicted with a blend, as on a cube. The top of the cone is created with adjacent triangular blends of different values radiating from the apex. There is more contrast between the light and dark areas on the narrow pan of the cone than on the wide pan.
A fir tree is cone-shaped. Look for triangular areas of light and dark.
Adjacent triangular blends radiating from a point describe cones.
The Sphere
A sphere is made of two shapes, a crescent and an oval. Depending on the angle of the light hitting it, the sphere is a combination of light crescent (its lit side) and dark oval, or dark crescent (its shadow side) and light oval. A sphere illuminated so its light and dark sides are evenly divided, and thus represented as two half-circles (one light, one dark), will look only somewhat three-dimensional. When l have to draw such spheres, I usually adjust the shadow and light to form subtle crescents and ovals, because I know that this will enhance the illusion of three-dimensional form.
On spheres, the light and shadow shapes are crescents and ovals (actually ovoids, or oval-like shapes).
An oak tree resembles a half-sphere. Look for a partial crescent or oval on its shadow side.
The Torus
The torus is a combination of the cylinder and the sphere. The middle portions of a torus are curved cylinders. Where the cylinder curves back on itself, the torus looks like portions of a sphere. As defined by value shapes, the middle of the torus is seen as curving parallel stripes and the returning curves are seen as portions of crescents or ovals.
The torus combines the light and shadow shapes of spheres and cylinders. The middle portions of a torus are usually defined by curving parallel stripes. The returning curves are portions of crescents or ovals.
This piece of rope is a torus. Look for the distinguishing light and shadow shapes of its form.
In observing forms, take note of the following:
- When we see a single value, we are seeing a plane that is parallel to the picture plane
- When we see values as an even blend, we are seeing a plane that is not parallel to the picture plane.
- When we see values as blends of parallel stripes, we are seeing cylindrical forms.
- When we see values as blends of adjacent triangles, we are seeing conical shapes. And we expect to see a little more contrast between darks and lights at the point than at the wide part.
- When we see values forming crescents and ovals, we are seeing spherical shapes.
This form combines a cylinder and a cube. Notice how with each change in plane there is a change in value.
The object on the right combines a cylinder and a cube. Notice the treatment of its corners and how they differ from those of the object at left.
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