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- Images in transformation: The color and its change in a group of Portuguese paintings from the second half of the 16th centuryPublication . Melo, Helena Pinheiro de; Cruz, António João; Sanyova, Jana; Valadas, Sara; Cardoso, Ana Margarida; Candeias, AntónioFour panel paintings depicting episodes related to the birth of Christ and attributed to the Portuguese mannerist painter Francisco João (doc. 1558–1585) were found to exhibit a muted palette that had no correspondence with the traditionally vivid colors used in the sixteenth century to represent joyful biblical events. Complementing previous research on the disruption and loss of the red glazes in these paintings, the investigation focused on the analysis of materials, painting technique and degradation issues that further affected the original paintings, changing the viewer's perception and understanding of these artworks. The investigation combined the visual examination of the painting surface with microscopic and spectroscopic analysis of the binder and pigments. A conventional palette made of lead white, lead-tin yellow, ochres, vermilion, verdigris, smalt, azurite, carbon black and a red lake made of brazilwood and cochineal was identified. The pigments were bound in an oil-based medium. Chemical and physical alterations detected in paints rich in smalt and verdigris were found to be responsible for color changes affecting significant areas of the compositions. The presence of moisture and the reaction between pigment and binder leading, among other products, to soap and oxalate formation, played a central role in the long-term behavior of the paint film. Understanding the main degradation processes involved and their consequences is crucial when interpreting an artists' color palette and designing the best approach to preserve these paintings.
- The Matter from Which an Orange Colour Is Made: On the Arsenic Pigment Used in a Portuguese Mannerist PaintingPublication . Cruz, António João; Melo, Helena P.; Valadas, Sara; Miguel, Catarina; Candeias, AntónioThe painting The Descent from the Cross, painted in 1620 by Pedro Nunes (1586–1637), presents two large figures with orange-coloured fabrics with conservation problems. Through the analysis of two samples with several analytical techniques, especially scanning electron microscopy combined with X-ray spectroscopy and Raman microscopy, it was possible to conclude that the orange colour is due to a complex artificial pigment made of amorphous arsenic sulphide. It essentially consists of spherical particles obtained by sublimation and condensation, possibly from orpiment, which ended up being joined with irregularly shaped particles resulting from crushing of the residual fraction obtained by solidification and fusion. This is a rare documented case of the extensive use of artificial arsenic sulphides in European easel painting, especially outside Italy. The conservation problems can be explained by the great sensitivity of the arsenic sulphides to photodegradation and the formation of powdery compounds.
- Caracterização através de análise química da escultura portuguesa sobre madeira de produção erudita e de produção popular da época barrocaPublication . Barata, Carolina; Carballo, Jorgelina; Cruz, António João; Coroado, João; Araújo, Maria Eduarda; Mendonça, Maria HelenaMaking use of several analytical techniques, four erudite and four popular Portuguese baroque wooden sculptures were studied. The materials and techniques employed were identified and the relationship between their artistic quality and the materials used was investigated. In general, the pigments were common at the time, but one pigment discovered in the beginning of the 18th century and two rare arsenic pigments were also identified. In popular sculptures cost-saving was detected, particularly concerning the gold leaf. Regarding some technical procedures identified, recommendations found in historical documents did not seem to have been entirely followed, neither in erudite nor in popular sculptures.