Images in transformation: The color and its change in a group of Portuguese paintings from the second half of the 16th century

Abstract

Four panel paintings depicting episodes related to the birth of Christ andattributed to the Portuguese mannerist painter Francisco Jo ̃ao (doc. 1558–1585) were found to exhibit a muted palette that had no correspondence withthe traditionally vivid colors used in the sixteenth century to represent joyfulbiblical events. Complementing previous research on the disruption and lossof the red glazes in these paintings, the investigation focused on the analysis ofmaterials, painting technique and degradation issues that further affected theoriginal paintings, changing the viewer's perception and understanding ofthese artworks. The investigation combined the visual examination of thepainting surface with microscopic and spectroscopic analysis of the binder andpigments. A conventional palette made of lead white, lead-tin yellow, ochres,vermilion, verdigris, smalt, azurite, carbon black and a red lake made of brazil-wood and cochineal was identified. The pigments were bound in an oil-basedmedium. Chemical and physical alterations detected in paints rich in smaltand verdigris were found to be responsible for color changes affecting signifi-cant areas of the compositions. The presence of moisture and the reactionbetween pigment and binder leading, among other products, to soap and oxa-late formation, played a central role in the long-term behavior of the paintfilm. Understanding the main degradation processes involved and their conse-quences is crucial when interpreting an artists' color palette and designing thebest approach to preserve these paintings.