source was being used, but it is believed to have been copper ores. During the New Kingdom, evidence has been found 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. The presence of tin oxide could have come from copper ores that contained tin oxide and not from the use of bronze. However, no copper ores have been found with these amounts of tin oxide. Why a switch from the use of copper ores in earlier periods, to the use of bronze scrap during the Late Bronze Age is unclear as yet. The total alkali content in analyzed samples of Egyptian blue is greater than 1%, suggesting the alkali was introduced deliberately into the mixture and not as an impurity from other components. Sources of alkali either could have been natron from areas such as Wadi Natroun and El-Kab, or plant ash. 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 plant ash 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. The alkali source likely was natron, although the reasons for this assumption are unclear. However, analysis by Jaksch et al. of various samples of Egyptian blue identified variable amounts of phosphorus (up to 2 wt %), suggesting the alkali source used was in actuality plant ash and not natron. Since the glass industry during the Late Bronze Age used plant ash as its source of alkali, a link in terms of the alkali used for Egyptian blue before and after the introduction of the glass industry might have been possible. Archaeological evidence Amarna In the excavations at Amarna, Lisht, and Malkata at the beginning of the twentieth century, Petrie uncovered two types of vessels that he suggested were used in antiquity to make Egyptian blue: bowl-shaped pans and cylindrical vessels or saggers. In recent excavations at Amarna by Barry Kemp (1989), very small numbers of these "fritting" pans were uncovered, although various remaining pieces of Egyptian blue 'cake' were found, which allowed the identification of