crystals, also producing lighter shades. The earliest appearance of blue frit is as a pigment on a tomb painting at Saqqara dated to 2900 BC, though its use became more popular in Egypt around 2600 BC. Blue frit has also been uncovered in the royal tombs at Ur from the Early Dynastic III period. Its use in the Mediterranean dates to the Thera frescoes from the Late Middle Bronze Age. While the glass phase is present in blue frits from Egypt, scientists have not detected it in blue frits from the Near East, Europe, and the Aegean. Natural weathering, which is also responsible for the corrosion of glasses and glazes from these three regions, is the likely reason for this absence. At Amarna, archaeologists have found blue frit in the form of circular cakes, powder residues, and vessel fragments. Analysis of the microstructures and crystal sizes of these frits has allowed Hatton, Shortland, and Tite to deduce the connection among the three materials. The cakes were produced by heating the raw materials for frit, then they were ground to make powders, and finally, the powders were molded and refired to create vessels. In On Architecture, the first century BC writer Vitruvius reports the production of 'caeruleum' (a blue pigment) at Pozzuoli, made by a method used in Alexandria, Egypt. Vitruvius lists the raw materials for caeruleum as sand, copper filings, and 'nitrum' (soda). In fact, analysis of some frits that date to the time of Thutmose III and later show the use of bronze filings instead of copper ore. Stocks suggests that waste powders from the drilling of limestone, combined with a minor concentration of alkali, may have been used to produce blue frits. The powders owe their copper content to the erosion of the copper tubular drills used in the drilling process. However, the archaeological record has not yet confirmed such a relationship between these two technologies. Green frit Evidence of the use of green frit is so far confined to Egypt. Alongside malachite, green frit was usually employed as a green pigment. Its earliest occurrence is in tomb paintings of the 18th dynasty, but its use extends at least to the Roman period. The manufacture of green and blue frit relies on the same raw materials, but in different proportions. To produce green frit, the lime concentration must outweigh the copper concentration. The firing temperature required for green