Detecting traces of invisible Egyptian Blue on a limestone stela fragment with reflection, luminescence and spectroscopic techniques

Abstract

Many stone artefacts from antiquity—including stelae and statues—were frequently decorated with vivid colours. Today, these have mostly faded or entirely disappeared, being no longer visible to the human eye. This case study explores several non-invasive methods to monitor, detect, and identify the traces of ancient Egyptian pigments on a limestone medium, particularly focusing on Egyptian Blue. The selected object is a fragment of a limestone stela decorated with an incised and coloured offering scene, dating to the early New Kingdom (ca. 1550–1292 BCE). The applied methods are reflection photography, visible-induced infrared luminescence (VIL), white light multi-light reflectance (WL MLR), and mobile X-ray fluorescence spectroscopy, both point (pXRF) and mapping (p-µXRF). The applied techniques, which vary in user complexity and user accessibility, substantiate the presence of the Egyptian Blue pigment and others on the relief when used all together, but equally indicate how the methods can be used separately for the same purpose.