Pigment

Background:  

When it comes to coloured artworks, the artists require some material for colouring the artworks. There are various types of material available for colouring. One of the common materials is pigment.  

Pigments

Preparation of pigment - grinding pigment with muller on granite slab

What is Pigment?  

A pigment is mostly a dry colouring matter which is ground into a fine powder. This material can change the colour of reflected or transmitted light is called a pigment. This is due to the wavelength-selective absorption property of the pigment. This powder is then mixed with water, oil, or any other binder, which is relatively a colourless material to produce paints and similar products.  

Difference between Dyes and Pigments:  

Though both dyes and pigments are used for colouring, there are some differences between the two. While dyes are usually soluble in water, pigments are completely or nearly insoluble in water. Dyes are generally organic compounds, while pigments are generally inorganic compounds.  

History of Pigments:  

Mankind has been using minerals for colouring since prehistoric times. The primitive man started using paints for decorating the body. Pieces of evidence have been found in caves regarding use of pigments and paint grinding equipment. These items are believed to be between 350,000 and 400,000 years old.  

The pigments are usually named after the city or region where they were originally mined. For example, Raw Sienna and Burnt Sienna were originally mined in Siena, Italy. Similarly, Raw Umber and Burnt Umber were mined for the first time in Umbria. These pigments were among the easiest to synthesize and became the basis for creating modern colours   

Apart from these naturally available pigments, synthetic pigments were also available. These earliest synthetic pigments were chemical compounds, which had colouring property. Some of the examples of synthetic pigments are White lead (basic lead carbonate, (PbCO3)2Pb(OH)2) is one example, Blue frit (calcium copper silicate). Later some more pre-modern synthetic pigments were also used by artists, which included vermilion, verdigris, and lead-tin-yellow. Indian Yellow was once produced by collecting the urine of cattle that had been fed only mango leaves.  

These days most organic pigments are synthesized from aromatic hydrocarbons. These are compounds benzene as the main compound where 6 carbon atoms are attached to 6 hydrogen atoms in the form of a closed ring. Organic pigments include azo, which contain a nitrogen group; and is mostly used as organic red, orange, and yellow pigments. Copper phthalocyanines provide brilliant, strong blues and greens that are unusually colourfast for organic colours. Some pigments, such as fluorescent ones, are simply dyes that have been rendered insoluble by chemical reactions.   

How do pigments work?  

When the white light falls on any object, then the object absorbs some colours and reflects one or more particular colours(s). This determines the colour of that object. A black object absorbs all colours and reflects nothing. Similarly, a white object reflects all colours and absorbs nothing.  

The same principle is valid for pigments as well. The colour of a pigment is also determined by the wavelength of the visible spectrum that it absorbs and reflects. Like all materials, the colour of pigments arises because they absorb only certain wavelengths of the visible light (VIBGYOR). The bonding properties of the material determine the wavelength and efficiency of light absorption. Light of other wavelengths is reflected or scattered. The reflected light spectrum defines the colour of that pigment.   

The colour of pigments is sensitive to the source of light. For example, the solar light is fairly uniform in the spectrum and also has a high colour temperature. So, the pigment shows its true colour. All other artificial light sources have less uniformity. Hence, the pigment dies not to show its true colour.  

Other properties of a colour, such as its saturation or lightness, may be determined by the other substances that accompany pigments. Binders and fillers can affect the colour.  

Colour coding of pigments:  

The colour of pigments is given certain numerical codes to specify its light source. Unless specifically noted and mentioned, the lac colour numerical code is mentioned as D65 light source, or "Daylight 6500 K", which is roughly the colour temperature of sunlight.