Pigments are very fine powder that have their own color, and they are color material for paint. Paints are mainly made of pigments and binders. Pigments must not dissolve into binders ( color materials whitch can be dissolve into medium are not pigment but "Dye". For exanple , in case of oil paint , pigments disperses as powder in paints and stays in their films on the canvas ( dose not ooze out of the film s) .
Each pigments have their own chemical and physical properties. As inportant characteristics of each pigments , we shold know about their properties of oil absorption , light resistance , weather resistance , Drying rate , poison , tinting strength , hiding power etc. See and check about each pigments by "the pigment table"
In case of oil paint , the drying rate of each paints depends on the amount of vihivle and the cemical properties of pigments. Genelary, As the amount of vehicles are large, the drying rate of the paint will be slow. The amount of vehicles that are required to make oil paints depends on the oil absorption of pigments. And pigments affect to the drying ability of paints by their cemical properties. E.g. the metal substance included in Silver white, Umber, etc. helps the dryness of drying oils like a siccative.
Some pigments can not be mixed with specific pigments. For example, White lead will be darkened or blackened when it's mixed with Ultramarine , Vermilion , Cadmium-red or the like , because of thier chemical reactions. Those darkening hardly happens between resent pigments manufacturers refined , but we should avoid bad combinations just in case.
As the size of particle of pigment is small , the area of surface become large. As a result , the paint need large amount of binder to wet each of pigment particles. The amount of oil that is required to make paint with a pigment is called oil absorption. The oil absorption of a pigment depend on not only the size of particle but various physical and chemical properties of the pigment and also binder. For example , Yellow orhcer and Raw sienna have similar colour , but the second needs greatly amount of oil compare with the first. The amount of oil affects the time of dryness. In general , large amount of oil causes yellowing and delay of dryness. Therefore , some technical books advice us to remove raw sienna from our palette.
Each pigments have their own properties of fastness against light , moisture , gases , acid , alkali , etc. E.g. the fastness of pigments against lights is called "lightfastness" or "light resistance". Pigments which have poor fastness against acid can not be used in oil vehivles. And pigments which have poor alkali resistance can not be used with fresco method or acrylic resins.
Chalk provides bright whiteness when it's used in tempera or watercolor medium. But in drying oils it becomes colorless and nearly transparent. Pigments which become colorless in the vehicle, such as chalk are called "Inert" or "Inert pigment". Chalk(calcium carbonate) , Gypsum , Barium white , Almina White and the like in oil paints are known as Inert pigment. Inert pigments are used as basis for lake pigments , extender or adulterant for colored pigments.
As for oil paint, dyes doesn't stay in own drying films on the canvas and stay away to other piants or layers. It can not be used in vehicles by itselves. Therefore manufacturers precipitate dyes upon inert pigments to make oil paints. And then they mix them with vehicles. Those color materials are called "Lake".
Carmain , Crimson lake, etc. are known as typical lake pigments. Precipitating dye on inert isn't perfect in present technology. You shouldn't use lake pigments for grounds or under paintings. Sometimes dyes r ed on inert to upper films and dyes them. E.g. when you paint a white over a film of crimson lake, the upper white will be dyed into pink color. This penomenon is called "Bleeding"
Manufacturers add Inerts into their paints to control the tinting strength or hiding power of the paints. Some pigments have very strong tinting strength and poor hiding power. It's difficult to use or mix those pigments for beginners. Inerts put down the tinting strength. And they also save the hiding power of high hiding powered pigments and put up the hiding power of low hiding popered pigments. Inerts for those use are called "Extender".
Though the proper amount of inerts are good for paints, some manufacturers add too much inerts into their paints to increase amount of the paints, because most inerts are cheaper than colored pigments. Sometimes inerts are more than colored pigments in the paint. Inerts for this use are called "Adulterant".
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