The color of opaque objects depends not only on their ability to reflect light. Color perception is also influenced by:
For example, if the enamel layer is transparent and thin, light passes through it, reflects off the material underneath (the substrate), and returns. In this case, the color is determined by both the properties of the enamel and the properties of the substrate.
If the enamel layer is thick and opaque, light is reflected mainly from the paint layer itself. In this situation, the color of the surface depends only on the properties of the enamel.
The nature of light reflection also depends on the condition of the surface.
Rough surface
If the surface is rough and the lighting is diffuse, the reflected light is distributed in all directions. Therefore, regardless of the angle at which we look at the surface, part of the surface-reflected light always enters the eye.
In this case, the perceived color is formed as a mixture of:
Smooth surface
If the surface is smooth and the lighting is directed, the surface reflection has a clearly defined direction.
In a certain position of the observer, the surface-reflected ray may not enter the eye. Then the color is determined mainly by the light that has passed through the paint layer and reflected from the deeper layers of the material.
If the paint layer consists of optically heterogeneous materials, light passing through it is:
As a result, light flows reflected from different depths of the layer reach the observer. This also affects the final perception of color.
In the international measurement system, color is described by three basic colorimetric values:
Together, these three parameters allow any color to be described accurately.
Hue determines what color we see: red, yellow, green, blue, etc.
However, hue alone is not enough to fully describe a color. The same hue can have many shades.
Color purity characterizes the degree to which a color is diluted with white pigment.
For example, if white pigment is added to colored enamel:
Colors that do not contain white pigment are perceived as the most vivid and saturated.
Color purity is measured in percentages:
The combination of color tone and color purity is called colorfulness.
However, even these two parameters are not enough to fully describe a color.
The third important characteristic is lightness.
Lightness determines how light or dark a color appears.
For example, if part of a sheet of paper is shaded from direct sunlight, one part will appear darker and the other lighter, even though both are the same color.
A similar effect occurs when black pigment is added to paint:
Color is completely determined by three characteristics:
Even a slight change in any of these characteristics leads to a change in color.
That is why, when preparing and correcting color, the colorist must carefully control all three parameters.