IRFANA P K
Dyes

Dyes , colouring materials that are applied as a solution and cling to whatever they are applied to can be used for decorative, aesthetic, and artistic purposes. It is a coloured substance that chemically bonds to the subtsrate to which it is being applied. Dyes are intensely coloured or fluorescent organic substances only, which impart colour to a subtsrate by selective absorption of light.
Pigments
Pigments are used in paints, inks, plastics, fabrics, cosmetics, and food. It's insoluble materials that have to be mixed with binders or vehicles to attach them to a subtsrate. Inks are liquids or pastes that contain dyes or pigments.

Colour and Colour vi-sion

Colour an attribute of things that results from the light they reflect,t ransmit, or emit in so far as this light causes a visual sensation that depends on its wavelengths.
Colour attributes were first understood by 19th century physiologist Ewald Herring. The primary colours are red, yellow and blue. The three secondary colours are green, orange and purple .created by mixing two primary colours. Magenta, cyan and yellow colours are secondary colours. Another six tertiary colours are formed by mixing primary and secondary colours .such as red-orange, red-purple, Yellow-orange, yellow-green, blue-purple & blue-green. Colour vision is an abiltiy of animals to perceive differences between light composed of different wavelengths. Photoreceptors in the retina are called rods and cones. Rods are more plentiful there are approximately 100 million rods in the human retina .Colour vision is possible due to photoreceptors in the retina of the eye known as cones. Achromatopsia is a condition characterized by a partial or total absence of colour vision.

Dyes
and
Pigments
Dyes are Soluble Lower as compared to pigments during application process there is a temporary alteration in the structure of the dyes. Dyes can only impart colour by selective absorption of the dyes usually the dyes are organic compounds pigments are normally inorganic compounds, often involving heavy toxic metals. In case of ink based printing prints made with pigments lasts longer. Traditionally pigments have been found to be more lightfast than dyes.