Color and Light
The color of a pigment comes from the effect light has on the eye. Many conditions can effect this color, and two examples of the same pigment may not match exactly unless they are viewed under the same conditions. When a dry pigment is mixed with a liquid its color is changed to a darker tone. The materials used as pigments differ wildly in certain properties from the liquid used as a medium. One of these properties is the amount of light a substance reflects and absorbs. As all solids and liquids differ from one another in this manner so they have been tagged with a number as its refractive index. A sheet of glass is transparent, when a ray of light strikes it there is a varying amount of surface or mirror like reflections. Depending on conditions the greater part of the light passes through and emerges refracted or bent, at an angle different from which it entered. The refractive index is computed from this change in angle, which can change depending on each case of the substances power to impede light rays.
When two substances of varying refractive indices meet there will be a proportion of light reflected at the point where they meet, the greater the difference the more of this effect you will see. When a pigment with a refractive index of 2.00 is dry, each particular being surrounded by air the index of which is 1.00, a certain amount of white light is reflected. When the pigment is moistened with linseed oil much less light is reflected as more is absorbed, and the hue will appear darker or more intense in color. Substances such as glass or ice appear transparent, but if you pulverize glass or shave ice it becomes an opaque white. This happens because light has much easier time passing through the uniform substance. When it strikes the powdered form the light is diffused in all directions and has a harder time passing through the tiny particles. When a piece of glass has been rubbed with an abrasive to created a frosted appearance the light is broken up, but as the glass has only been altered in a thin layer on the surface the light is not entirely impeded and can continue through the glass. This causes a translucent appearance instead of transparent.
A flat or mat effect on a paint or varnish film is due to these irregular construction. When such a surface is moistened its opacity is temporarily diminished. In the same way, alumina hydrate, a white, opaque powder when dry, will become colorless and transparent when wet with benzol because the particles are then surrounded by a medium which has a refractive index very close to its own. The effect of liquids upon the color and opacity of pigments varies greatly in each case, depending on these differences in their refractive indices.
It will be seen that when light impinges upon an object it is either transmitted, reflected, or absorbed, depending on the nature of the object. In the case of most paints it preforms all three of these actions, in varying degrees. The practical lesson from this is the ground and underpainting always have some kind of effect on the final piece, even when its not apparent, and that pictures must be built up carefully with this point in mind. Correct painting procedures calls for keeping the ground and underpainting as white or as pale as possible. Even going to the extent of scraping off or removing any substantially thick or dark areas when corrections are needed to be made. If two pictures where painted in the exact same manner except one was done on a white ground and the other on a black ground these differences would become apparent. Not to say painting on black canvas is a bad thing, but it must be stated that where you start is going to have an effect on the appearance of where you end.
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Your continued support is much appreciated. I'm glad you guys are enjoying this journey through education of the arts as much as I am. In arts recent past "education" has been a very low priority for many artists, limited to only learning the application and completely ignoring the technical. My goal with these posts are to change that idea as its clearly having an affect on the art community.
