Chemical and Physical Investigations of Egyptian and Chinese Blue and Purple

Abstract

The production of Egyptian Blue can be traced back from earlier than 3000 B. C. up until approximately 300 A. D. One of the earliest documentation of Egyptian Blue is found on the Tablets of an olive oil container, which certifies the quality of the oil blessed by the Godcss Iset (prc-dynastic). Another proof for the early use of Egyptian Blue is the Mastaba of the vesir of Mcrcruka (2300 B. C , Saqquara). This and other samples are shown in Table 1 and represent a selection of identified Egyptian Blue up to the Greek-Roman period. A contemporary artist, E. Arpagaus, has studied mineral colours and pigments of Egypt and surrounding areas (Arpagaus, 1996) showing the variety of different colours, which were prevalent in nature. The presented blue pigment has however been artificially produced in the manner of the Egyptians. In ancient times continents and countries were connected by famous trade routes; the link between the Western World and ancient China was established via the Silk Road. Aside from its economic function this adventurous and risky route played an outstanding role in the distribution and exchange of ideas and technologies between East and West. The relatively constant composition of Egyptian Blue over the period of the Old Kingdom up to the Ptolemaic and Greek-Roman time (Table 2) indicates that the information about the production of coloured pigments never got lost. For blue pigments this is attributed to the fact that they had a prominent role in religious rites and everyday life. States adjoining the Silk Road were challenged by the tradition of blue production and its use in manufactured Egyptian goods to either obtain it by trade or to produce it themselves. This background was apparently a major driving force for the expansion of artificial blue and even other pigments. The change in location and the need for further improvements of artificial pigments induced new technological developments, which generated similar advanced materials such as strontium and barium copper silicates as in the Iraqi and Iranian samples of Brick Nimrud (British Museum London) the Sistrum Hasanlu and the Goblet Hasanlu. Iran (both Metropolitan Museum New York) and barium in Chinese artefacts represented by the blue and purple octahedral sticks and samples of the Terracotta Army, all compiled in Table 1. The Chinese samples are attributed to the Warring States, Quin and Han period 600 B. C. till approximately 200 A. D.. As we will see in the later context they contain man-made blue and purple pigments called Chinese Blue and Purple, sometimes also denoted as Han Blue and Purple (Fitzhugh. 1992). They were used in colouring applications and they refer to destine!, but very related chemical compounds. Only Egyptian and Chinese Blue are found as minerals in nature (Cuprorivaite. F.ffenbcrgerite (Gicster, 1994)). They are, however, so rare that any utilization of these minerals by ancient civilizations can be excluded. It should be mentioned at this point that the only mineral pigment used by earlier civilizations, which naturally appeared blue and did not demand chemical t ransformation or processing, was lapis lazuli (Reincn, 1999). Its scarcity in nature caused it to become highly es teemed at least in the western hemisphere. Presumably as a consequence of the general scarceness, the blue has been attributed divine character in some civilizations, such as the Egyptian. In general colour has played a major role in the development of civilizations and has acquired important cultural functions as one of the essential ways of human self-expression and affectation. Colours produce aesthetic stimulation, which is reflected in art forms. All this emphasizes the outstanding role of colour in human development, and colouring substances in the form of pigments have thus always been used by mankind as they became available. Apparently motivated by the lack of natural blue minerals and mankind's intrinsic desire for colours, people were driven to invent blue pigments. It is may be worth mentioning that among those invented Blues there is also the Indigo based Maya Blue, which had wide-spread application within Indian cultures (JoseYacaman, 1996). Any of the mentioned man-made blue pigments but also Chinese Purple required sophisticated chemical and technological developments, which could only be mastered in a sound cultural and technological environment. In the following article we will see that the chemistry behind these manmade pigments is quite complicated. Ancient chemical achievements could not be based on atomic or molecular grounds. Therefore any progress was established by long and tedious processes of empirical probing.