Historical grisailles characterisation: A literature review

This work presents the first review on the characterisation of grisaille stained-glass paint, in order to follow the evolution of the production materials and methods throughout time and provenance. From the literature review, 38 scientific studies regarding the grisaille paint were found, dated between 1984 and 2020. In these works, various samples from the 13^th to the 20^th centuries belonging to 11 different European countries were characterised. In general, iron oxide was the main colouring agent identified throughout the centuries and countries, except in the Central and South-Central European countries where copper oxide was preferably used. Different metal oxides, such as cobalt, chromium and manganese were also identified in modern samples (19^th and 20^th centuries), used together with iron oxides. The base glasses generally presented a lower ratio PbO:SiO₂ (~0.5 to 1) than the expected from the historical recipes, and the addition of borax is suggested for grisailles from the 17^th century onwards. The proportion between the base glass and colouring agents showed ratios between 1 and 1.5, related to well-balanced grisailles. The present overview, critical analysis and comparison of published studies regarding this glass-based paint allow to draw a spatio-temporal map of the grisaille composition evolution, which reflects the changes in composition regarding the country of provenance and century.