A Note on the Examination of Silverpoint Drawings by Near-Infrared Reflectography

Abstract

A group of 17 Italian fifteenth-century metalpoint drawings were examined using near-infrared reflectography and analysed non-invasively by X-ray fluorescence and Raman spectrometry. Metals, including silver and lead, reflect infrared (IR) radiation specularly and selectively. As expected, all of the lead-based metalpoint in this group of drawings proved to be entirely opaque when examined by IR reflectography. However, the silver-based metalpoint found on these drawings was observed to be wholly or partially transparent to infrared radiation in the 800–1700 nm range. The results obtained on drawings were compared with those from reference material of known composition. The response of silver-based metalpoint to infrared radiation is here attributed to the presence of silver corrosion products, particularly silver sulphide (Ag₂S), a commonly encountered degradation product of silver. This compound shows high transmission in the spectral range under investigation.