Heinz Berke, professor of inorganic chemistry at the University of Zürich, Switzerland, looks at the use of manmade blue and purple pigments by ancient civilizations

 

Colours are an intrinsic part of human life. They produce aesthetic stimulation and they fascinate. They are the means of expression in art and they form part of human culture. 

In prehistoric times, only the so-called earth colours, colours provided by the surface soil, could be used as pigments. Blue is not an earth colour and so was not available to prehistoric humans as a pigment, nor is it provided by nature as a stable dye. 

Necessity, as the mother of invention, stimulated several ancient civilizations to develop artificial blue and purple materials by chemical synthesis. Egyptian Blue (CaCuSi₄O₁₀), the first synthetic pigment, was used in ancient Egypt in the Mediterranean area, Mesopotamia and Persia from around 3000 BC until the end of the Roman Empire. Han Blue (BaCuSi₄O₁₀) and Han Purple (BaCuSi₂O₆) appeared in a relatively small area of northwestern China from around 800 BC until the end of the Han Period in 220 AD. Maya Blue, a chemical intercalation compound of indigo (C₁₆H₁₀N₂O₂) and the white clay palygorskite (a magnesium aluminosilcate mineral), was used in Central America to paint houses and decorate artifacts from around 400 BC. 

 

Han Blue was developed in northwest China in 800 BC

Advances in ancient pottery techniques, for making compact blue objects, and glazing techniques, such as polychromic tile glazing, were closely related to the development of blue pigments. Blue and purple had thus made man's life more pleasant and had become highly esteemed in ancient times. 

In recent years, archaeology has profited greatly from progress in science. Advances in microanalytical techniques have allowed historical assignments to be made on the basis of hard scientific facts. The application of scientific techniques and methods to archaeology is called archaeometry. 

The archaeometry of ancient pigments has gained support from x-ray analytical methods, Raman spectroscopy and electron microscopy. Many questions about how ancient pigments were made can now be answered. For instance, the mysterious finding of significant amounts of lead in all the samples of Han Blue and Han Purple that have so far been analysed - it is now known that lead additives were used to accelerate the decomposition of the barium mineral starting materials. Such detailed conclusions could only be reached on the basis of laborious scientific analyses applying modern scientific methodologies. 

A possible technology transfer from Egypt to China is suggested by the chemical relationship of the Egyptian and Chinese pigments. For any transfer of knowledge and techniques, the areas of distribution of these pigments must have overlapped, but knowledge about the use of Egyptian Blue in Central Asia is still limited, so this question remains open. 

All the pigments described have one thing in common: they were all created by human inventive talent, which is strongest when there are situations of deficiency - even if the invention does not serve vital needs. In the case of blue pigments, chemistry was used as an opportunity. Chemistry was not only an opportunity for the people in ancient times and at the age of industrialisation, but still is an opportunity for the people of today. Seizing opportunities with chemistry means, according to the notable German chemist Justus von Liebig, to use 'silent force' and reach 'copious abundance'. 

 

Read Heinz Berke's review on 'The invention of blue and purple pigments in ancient times' in issue 1, 2007 of Chem. Soc. Rev.