controlled by testing of firing materials, the size, shape, and material of the kiln, and the control of the environment. Technology for achieving and maintaining high temperatures would have been known from metal and ceramic production e.g. the potential use of twin bellows as used in metal production. Comparison History Hypothesis on origin Han blue and Egyptian blue have the same basic structure and have very similar properties. The main difference is that Egyptian blue (CaCuSi4O10) has calcium in the position of Han blue's barium (BaCuSi4O10). The similarity lead some to suggest that Han blue was based on Egyptian blue knowledge, which had traveled east along the Silk Road. Independent innovation in China would still have been needed to replace calcium with barium (the Han pigments start to form at 100 – 200°C higher than the Egyptian blue). The two hypotheses underlying the speculations about the exact chronology of the invention of these blue pigments can be summarized as follows: That earlier alkali metal glazing techniques were based on knowledge from Egypt, but that the copper silicate pigments (Egyptian blue and Han blue) developed from these glazes in two independent areas: Egypt and China. Alternatively, that examples of Han blue predate the official Silk Road and therefore that development was completely independent. Chinese invention The case against links with Egyptian blue includes the absence of lead in Egyptian blue and the lack of examples of Egyptian blue in China. The use of quartz, barium, and lead components in ancient Chinese glass and Han purple and Han blue has been used to suggest a connection between glassmaking and the manufacture of pigments, and to argue for independent Chinese invention. Taoist alchemists may have developed Han purple from their knowledge of glassmaking. The lead is used by pigment maker to lower the melting point of the barium in Han Purple. The increase and decrease of barium glasses, and Han purple and Han blue, follow similar patterns. Both peaked in the Han dynasty, declining afterwards. Pre-Han to Tang dynasties see a shift from lead-barium-silicate type glass to lead-soda-lime glass. The reason for decline is debatable. Liu et al. attribute the decline to the decline of Taoism when Confucianism was introduced, since they link pigment manufacture to the ideology of Taoism. Berke (2007) believes that political changes stopped the distribution of the pigments as the Chinese Empire was split at the end of the