Nucl. Tracks Radiat. Meas., Vol. 14, Nos 1/2, pp. 321-327, 1988 Int. J. Radiat. AppL Instrum., Part D Printed in Great Britain 0191-278X/88 $3.00+ 0.00 Pergamon Press plc THE THERMOLUMINESCENCE (TL) OF EGYPTIAN BLUE M. SCHVOERm~, M.-C. DELAVERGNE and R. CHAPOULIE Centre de Recherche Interdisciplineaire d'Arch6ologie Analytique, Laboratoire de Physique appliqu6e l'Arch6ologie, M.S.H.A., Universit6 de Bordeaux 111-CNRS, Domaine Universitaire, F-33405 Talence Cedex, France (Telephone 56.80.84.43) (Received 9 October 1987; in finalform I I December 1987) Abstract--Egyptian Blue is a synthesized crystalline pictorial pigment with formula CaCuSi40~0. It has been used in Egypt and Mesopotamia from the 3rd millenium B.C. A preliminary experiment on a recently synthesized sample showed that this pigment is thermoluminescent after fl irradiation (9°Sr). As the signal intensity grows linearly with the administered dose within the temperature range commonly used in TL dating, we have been looking for this phenomenon from archaeological pigments. It was encountered with two samples found in excavation. From its intensity and stability we concluded that Egyptian Blue can be dated using TL. This first and positive result encouraged us to extend the method to other types of mineral pigments synthesized by early man, and to suggest that it may be used for direct dating of ancient murals. 1. THE PICTORIAL PIGMENT "EGYPTIAN BLUE" 1.1. Crystallographic and optical characteristics and crystallogenesis The crystal, CaCuSi40]0, described in mineralogy under the term of "Cuprorivaite" is better known in archaeology under the term of "Egyptian Blue" (Pabst, 1959). Its optical transmission area is situated between 3800 and 5300 A, with a maximum in the blue, around 4600 /~ (Ullrich, 1979). Its synthesis can be summarized as follows: a mixture of quartz, calcium salt, copper salt and flux such as soda or potash, heated at 900-950°C under normal atmospheric conditions for 24 h. 1.2. Archaeological and historical data An important bibliography covers the following points. (a) Egyptian Blue is one of the oldest pigments synthesized by man (Tite et aL, 1984). (b) Chemists from the 14th Century succeeded in their first attempt to characterize ancient material using this pigment (Fouque, 1889). (c) It is one of the very first ancient materials that was recreated in the laboratory (Lauri et al., 1914). Also known as Blue Frit it is mentioned under this name in the 14th dynasty (2720, 2560 yr BC) (Iversen, 1955); it was used to make small objects such as pearls, statuettes, amulets (Farag and Iskander, 1971). It does not appear to be known after the fall of Rome (Gettens and Stoul, 1966). Finally, it should be remembered that Theophraste mentions it in "Le trait6 des pierres" (Theophraste, from M. Hill, 1754) and Pliny in "Histoire naturelle" (Collection Bud~, de Saint Denis, 1972; Zehnacker, 1983). 2. TL OF EGYPTIAN BLUE, QUALITATIVE STUDY 2.1. TL emission from a mineral pigment A first experiment was carried out in Bordeaux in October 1980 on a recent sample of Egyptian Blue that was synthesized by Dr D. Ullrich from Berlin University (Ullrich, 1979); it was revealed that after fl irradiation (9°Sr) of known doses, an induced TL emission arises whose intensity at higher tem- peratures within the dating range grows linearly with the administrated dose. This observation was funda- mental since mineral pictorial pigments---metallic salts being electrical conductors and generally opaque--were said to show no luminescence; thus a research programme was initiated to investigate the datability of ancient paintings and supplementary disciplines such as characterization and the study of alteration-ageing process in pictorial coats and their supports. This programme began in 1984, following mettings with members from the "Ecole frangaise d'Arch6oiogie d'Ath6nes" from the "Mission Permanente du CNRS" in Karnak and from the British Museum of London. 2.2. Nature and origin of the samples Two pigments were studied, BDX 575, a recent pigment synthesised at Berlin University by Dr D. Ullrich (1979), and BDX932, an archaeological pigment. BDX 932 was discovered in Karnak (Luxor, Egypt) in the southwest angle of the Middle-Empire courtyard facing the "Akmenou", jubilee temple of Thoutmosis III. It was found in August 1984, 50 cm deep into the soil by the researchers of the "Mission Permanente du CNRS" in Karnak (J. C. Golvin and D. Le Fur). Some other coloured pigments (green, 321