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The Chemistry of Pigments

At the heart of every drop of paint, every thread of cloth, every bit of your brightly coloured phone case is a pigment. Pigments are the compounds added to materials to give them colour. Pigments are used in paints, inks, plastics, fabrics, cosmetics, and food.

Chemgrit-coatings-blog-pigments

At the heart of every drop of paint, every thread of cloth, every bit of your brightly coloured phone case is a pigment. Pigments are the compounds added to materials to give them colour. Pigments are used in paints, inks, plastics, fabrics, cosmetics, and food.


Get to know pigments

Pigments are brightly coloured, insoluble powders (brightly coloured liquids are called dyes). In most cases, the bright colour is a result of the material absorbing light in the visible spectrum.


Pigments are mixed with binders to attach them to a substrate. The resulting suspension—a paint—is used to coat materials and impart colour onto them. In industry, there are three pigment classes: absorption pigments (used in watercolour paints), metal effect pigments (used to create surface lustre), and pearlescent pigments.

Pigments are found in nature, such as ochre (a blend of iron oxides and hydroxides) and indigo (C16H10N2O2). They can also be synthetic pigments such as mauve (an aniline derivative) or white lead. White lead, one of the earliest synthetic pigments, is made by treating sheets of lead with vinegar. They are often more robust than dyes, which dissolve in the material they are colouring. Pigments can keep their colour for many centuries and withstand high heat, intense light, and exposure to weather or chemical agents.


The importance of paint pigments

Pigments form an important part of paint and coatings. The pigments used in paints generally consists of organic and inorganic materials and provides various benefits including:

· Solid base for binder reactions

· Resistance to ultraviolet light

· Powerful coating for surfaces

· Added colour, texture, and physical properties.


Organic pigments include carbon compounds and are responsible for a broad number of colours across commercial products. Organic pigments often come from from animal and vegetable origins such as Alizarin: Yellow (orange, and red shades), Phthalocyanine: (blue and green shades) and Quinacridone (violet shades).


Inorganic pigments derive from mineral origins and are considered metal compounds. These include siennas, umbers, and ochres that form within clays in the Earth. They can be synthetically created to produce signature colours such as "cobalt blue" and "titanium white."


Natural pigments are generally less expensive and originate from silica, mica, calcium carbonate, zinc oxide, and clays, whilst synthetic pigments include synthetic molecules such as calcined clay, pyrogenic silica, and blanc fixe for tougher products.

No matter which pigments you use for paint, the concentration of the pigment will alter the appearance of the paint.


Colours of the future

Scientists continue to find ways to make new and more extreme colours, pushing the limits of what is possible. Researchers and scientists have created a black paint made of vertically aligned carbon nanotubes arrays. This substance is able to absorb 99.995% of light making it the darkest substance on Earth.


For more information on pigments for the paint industry contact Chemgrit Coatings on www.chemgrit.co.za or athol@chemgritsa.co.za.


[Information sourced: https://inchemistry.acs.org]

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