2 RESEARCH BACKGROUND

For several years the restoration workshop of the Fundaci�n Tarea, Buenos Aires, has been involved in the preservation, chemical analysis, and historical and iconographic study of paintings from the Spanish colonial period now found in the churches, chapels, and museums of Argentina. The paintings vary in quality of execution, chronology and—of greatest interest here—origin. Among them are canvases that undoubtedly come from 18th-century Cuzco workshops, works produced by the P�rez Holgu�n circle in Potos�, and paintings done on the Puna plateau of northwestern Argentina or in the province of C�rdoba. The present study centers on a group of 106 works (see appendix), painted between 1610 and 1780, which are now found in the following locations: churches and chapels of the Argentine northwest, province of Jujuy; the Marqu�s de Sobremonte Provincial Historical Museum, C�rdoba; the Julio Marc Provincial Historical Museum, Rosario, province of Santa Fe; the Isaac Fern�ndez Blanco Municipal Art Museum, Buenos Aires; and the Casa de la Cultura E. y F. Burgos, Mendoza. This article describes the methods and results of the analysis of the blue pigments present in each painting selected.

The Fundaci�n Tarea's study is the first of its kind for South American colonial painting. Both qualitative and quantitative methods were used. First, chemical microscopy was carried out on cross sections or on unmounted samples. The specific microchemical tests used for each pigment are described in the section corresponding to the pigment. Scanning electron microscopy energy dispersive x-ray spectrometry (SEM-EDS) was also used to confirm the presence or absence of the suspected elements of each pigment. Polarized light microscopy was used only for the analysis of the azurite and smalt mixture. There have been several complete scientific studies of pigments and binders used in Mexican painting, especially during the pre-Columbian period (Carrillo y Gariel 1946). Since 1995, the Fundaci�n Tarea's effort has been augmented by a team of professors and researchers—chemists and art historians—from the University of Buenos Aires, which has made two important grants for scientific advances in the restoration and identification of artworks in the Argentine national patrimony.

The study of blue pigments quickly proved to be a suitable field for systematic analysis, promising substantial findings, because the identification of these pigments' origin and manner of production has always presented complex problems that have conditioned aesthetic judgment and historical assessment. In the canvases studied, the blues show obvious disparities in brilliance and saturation from one work to another, suggesting the presence of different pigments. The limited bibliography in existence until a few years ago indicated, without much basis in known chemical testing, the South American artists had used indigo (a blue of vegetable origin), azurite (a copper mineral), and, occasionally, ultramarine. Querejazu (1986) mentions Castilian blue (presumably ultramarine), a�il or indigo from Central America, polvos azules (blue powders), and azurite. This article considers the last two to be the same pigment. Recently, C. Tomkiewicz (1995) presented a technical study of colonial paintings that included Mexican, Peruvian, and Bolivian works. Her results corroborated several of our own findings about blue pigments used in South America during the 17th and 18th centuries (Tomkiewicz 1995).