Blue and green in the decoration of a Kushite chapel in Karnak, Egypt: Technical evaluation using low-tech, non-invasive procedures

•The Kushite chapel of Osiris Neb-ankh/Pa-wesheb-iad in Karnak.•Non-invasive, low-tech methods for the investigation of scant paint remains.•Visible-Induced Luminescence (VIL) for topographical distribution of Egyptian blue.•Green as an integral colour of ancient Egyptian painting.•Egyptian blue admixtures with yellow and white to enhance the symbolic meaning. Visible-Induced Luminescence (VIL) has become a widely accessible investigation tool to identify and image the presence of Egyptian blue on in situ wall paintings. Portable microscopy has similarly entered mainstream usage to examine painted surfaces in archaeological settings. A project to investigate the extremely scant remains of decoration of the 7th c. BC Kushite chapel of Osiris Neb-ankh/Pa-wesheb-iad on the north side of Karnak temple demonstrated the effective use of these low-tech, non-invasive procedures. In order to better understand the nature of the highly deteriorated painting, an interdisciplinary approach was adopted that combined these intensely practical in-situ investigations with a process of comparative evaluation and deduction, drawing on expertise from the fields of painting technology and Egyptology. Beyond expected confirmation of the widespread use of Egyptian blue as a pure color, the skilful and selective admixture of this pigment with yellow and white pigments was detected. This appears to have been used to enhance painted subject matter of particular symbolic importance. The study was the basis for recognising a conspicuous absence of green in the decoration, determining where green was once present, and – by evaluating factors of pigment impermanence versus durability – helping to define the likely nature of the missing pigment. Definitive pigment identification was not always possible, nor was it a primary aim, although the evaluative process employed is also the most efficient way of identifying analytical procedures that might still be required. Even without identification, the findings made in relation to the missing green were highly significant, providing important evidence of a technological shift in the use of greens in Late Period wall paintings, which parallels similar developments found on other Egyptian artefacts. A low-tech, iterative approach to painting investigation therefore has great validity.