Egyptian Blue - Sources

Sources

The main component of Egyptian blue was the silica, and it has been suggested that quartz sand found adjacent to the sites where Egyptian blue was being manufactured was its source, although there is no concrete evidence to support this hypothesis. The only evidence cited is by Jakcsh et al. who found crystals of titanomagnetite, a mineral found in desert sand, in samples collected from the tomb of Sabni (6th dynasty). Its presence in Egyptian blue indicates that quartz sand, rather than flint or chert, was used as the silica source. This contrasts with the source of silica used for glass making at Qantir (New Kingdom Ramesside site), which is quartz pebbles and not sand.

It is believed that calcium oxide was not added on its own in the manufacture of Egyptian blue, but introduced as an impurity in the quartz sand and alkali. It is not clear from this then as to whether the craftsmen involved in the manufacture realized the importance of adding lime to the Egyptian blue mixture.

The source of copper could have either been a copper ore (such as malachite), filings from copper ingots or bronze scrap and other alloys. Prior to the New Kingdom there is scarce evidence as to which copper source was being used, but it is believed to have been copper ores. During the New Kingdom, there is evidence for the use of copper alloys, such as bronze, due to the presence of varying amounts of tin, arsenic, or lead found in the Egyptian blue material. Some have argued that the presence of tin oxide could have come from copper ores that itself contained tin oxide and not from the use of bronze. However, no copper ores have been found with these amounts of tin oxide. It is unclear as yet, why there would have been a switch from the use of copper ores in earlier periods, to the use of bronze scrap during the Late Bronze Age. It is possible that reserves had run out.

The total alkali content in analyzed samples of Egyptian blue is greater than 1%, suggesting that the alkali was introduced deliberately into the mixture and not as an impurity from other components. Sources of alkali could either have been natron from areas such as Wadi Natroun and El-Kab, or plantash. By measuring the amounts of potash and magnesia in the samples of Egyptian blue, it is generally possible to identify which source of alkali had been used, since the plantash contains higher amounts of potash and magnesia than the natron. However, due to the low concentration of alkali in Egyptian blue, which is a mere 4% or less, compared to glass, for example, which is at 10–20%, identifying the source is not always easy. It has been suggested, nonetheless, that the alkali source was natron, although the reasons for this assumption are unclear. On the other hand, analysis by Jaksch et al. of various samples of Egyptian blue identified variable amounts of phosphorus (up to 2 wt %), suggesting that the alkali source used was in actuality plantash and not natron. Since the glass industry during the Late Bronze Age used plantash as its source of alkali, there might have possibly been a link in terms of the alkali used for Egyptian blue before and after the introduction of the glass industry.