Properties of Pigments
- Paints contain pigments of different colours mixed with a liquid which carries the pigment (the medium).
- In water colours, the finely ground pigment is suspended in water; when the water evaporates it leaves behind the pigment on the page.
- In spray paints, the medium is a volatile organic substance that quickly evaporates.
- It takes a long time for oil paints to dry. The oil does not evaporate, but hardens and reacts with air to form a flexible film; the oil protects the pigment and helps bind it to the surface being covered.
- Many of the pigments used in the past were hazardous in some way; the artists were oblivious to the risks they were taking to produce their masterpieces.
- Modern paints are much less toxic; house paints no longer contain lead compounds and toxic inorganic pigments are now being replaced by less toxic organic ones.
- When old art work is restored, many of the older pigments are replaced by modern ones; this is due to them being less toxic and also related to the fact that many of the older pigments may not be available.
- Modern pigments usually tend to be much more stable than their traditional counterparts.
During the 1980’s, Vincent Van Gogh’s "A Cornfield with Cypresses” was cleaned and remounted, giving scientists at the National Gallery the opportunity to examine the materials and techniques used by Van Gogh.
- The picture was photographed in daylight, ultraviolet and infrared light; this gave scientists information about the pigments used in different areas, for example, white zinc oxide fluoresces in ultraviolet light and emerald greed (copper and arsenic) absorbs infrared light, making areas appear black in infrared light.
- They also took small samples of different coloured paint from the painting and analysed them to find out which elements were present using atomic emission spectrometry; they also used a scanning electron microscope to analyse the miniscule crystals from which the paint is made.
- These investigations showed that Van Gogh used Chrome Yellow mixed with Zinc White and other pigments to create the different shades of the yellow in his cornfield.
Useful books for revision
Revise A2 Chemistry for Salters (OCR A Level Chemistry B)
Salters (OCR) Revise A2 Chemistry