An imaging and spectroscopic methodology for in situ analysis of ceiling and wall decorations in Colonial missions in Northern Mexico from XVII to XVIII centuries

• Published in: Heritage science 2020-09, Vol.8 (1), p.1-14, Article 91
• Main Authors: Casanova-González, Edgar, Maynez-Rojas, Miguel Ángel, Mitrani, Alejandro, Rangel-Chávez, Isaac, García-Bucio, María Angélica, Ruvalcaba-Sil, José Luis, Muñoz-Alcócer, Karla
• Format: Article
• Language: English
• Subjects: Ceilings; Chemical composition; Chemistry and Materials Science; colors in Latin american archaeometric investigations; Conservation; Decoration; dyes; False color infrared imaging; Fiber optics; FORS; Historical structures; Homogeneity; Indigo; Infrared imaging; Materials Science; Methodology; Mexican colonial missions; Missions; Non-destructive analysis; Optical fibers; Organic materials; Pigments; Research Article; Restoration; X ray fluorescence analysis; XRF
• ISSN: 2050-7445; 2050-7445
• DOI: 10.1186/s40494-020-00434-8

Almost three hundred Spanish colonial missions—or their remains—are scattered over the vast state of Chihuahua in northern Mexico. A few of them still display painted decorations on the wood ceilings and walls. The decorated areas vary greatly, from the whole ceiling of the main aisle to just a few square meters in a lateral chapel, and so does the conservation state of the paintings. In this context, the information regarding the paintings’ composition plays a key role in the restoration and conservation processes. For the gathering of such information, we propose a combined methodology for a fast, non-destructive and non-invasive characterization of such paintings with a minimum of techniques. This methodology includes false color infrared imaging as a first approach to determine the composition of large areas of the paintings and the homogeneity of the materials used in the painted areas, followed by small area analysis by X-ray fluorescence and fiber-optics reflectance spectroscopy. This methodology was applied to characterize the elemental and molecular composition of the decorations for four missions in Chihuahua in a fast and specific manner, revealing the use of a mix of mineral and organic materials including indigo and cochineal, and detecting differences between the missions. The methodology presented here can be easily applied for the study of a wider number of missions in Chihuahua and other regions to provide outstanding information of materials, pictorial techniques and deterioration conditions.