Determining the Thickness of Gold Leaf in Post-Byzantine Religious Panel Paintings Using Imaging μ-XRF

Thin gold leaves were frequently used to embellish post-Byzantine religious panel paintings. Measuring their thickness using non-destructive methods is essential for understanding the technology behind their creation and developing effective preservation strategies. This study describes a method for non-invasively measuring the thickness of these gildings using large-scale imaging micro-X-ray fluorescence (µ-XRF) spectroscopy. The method relates the intensity of the Au Lα X-ray characteristic transition to the thickness of the gold layer. The method offers precise measurements of gold layer thickness in the submicrometer range on gilded surfaces, while traditional methods based on the intensity ratio of the same element prove ineffective. The method was initially validated on a mock-up sample created using traditional gilding techniques. Subsequently, the gilding was examined on two case studies of Greek religious icons. The analysis accurately measured the thickness of individual gold leaves, approximately one hundred nanometers, and identified regions with multiple overlapping layers, corresponding to structures with up to four leaves. The findings confirm that this technique offers valuable quantitative insights into the materiality and artistic techniques of these cultural heritage artifacts.