The authenticity of a double-sided painted processional crucifix acquired as Spanish 13th century from a private collection in Barcelona was questioned shortly after the piece entered The Cloisters (Metropolitan Museum of Art) collection in 1955. At the time, a combination of connoisseurship and limited technical analysis was employed to conclude that the crucifix was a forgery. In this work, a re-examination was carried out in order to support or deny earlier conclusions. Pigments and ground layers were analyzed in paint samples by Raman microscopy, complemented by scanning electron microscopy-energy-dispersive x-ray spectroscopic elemental analysis. The results showed that the piece is a re-fabrication of a Spanish medieval cross, perhaps dating from the 14th century. Significant alterations were made in order to present the work as a rare example of its type.

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Among the thirty-six paintings ascribed to the Dutch seventeenth century artist Johannes Vermeer (1632-1675), Mistress and Maid, in The Frick Collection, stands out for the large-scale figures set against a rather plain background depicting a barely discernible curtain. Although generally accepted as among the late works of the artist and dated to 1667-1668, for decades scholars have continued to puzzle over aspects of this portrayal. When the painting was cleaned and restored in 1952, attempts to understand the seeming lack of finish and simplified composition were hampered by the limited technical means available at that time. In 1968, Hermann Kühn included Mistress and Maid in his groundbreaking technical investigation 'A Study of the Pigments and the Grounds Used by Jan Vermeer. ' In the present study, imaging by infrared reflectography and macro-X-ray fluorescence (MA-XRF) revealed significant compositional changes and drew focus to areas of suspected color change. Three of the samples taken by Hermann Kühn, and now in the archive of the Doerner Institut in Munich, were re-analyzed, along with a few paint samples taken from areas not examined in the 1968 study, using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and Raman spectroscopy. These analyses made it possible to further visualize detailed compositional elements in the background of the painting that were later painted out, and to characterize darkening and color changes in different paint passages.

The nature of ground preparations is of critical interest to those engaging in the study of historical painting techniques, as certain materials can be identified with specific regions and school of painting. This is the case of a particular ash-based, calcite-rich material obtained as a byproduct of lye production, recently identified for the first time in ground preparations by means of chemical analysis, and which is considered specific to Baroque artists of Spanish school. Because of limitations in the size of the samples that can be removed from works of art, and because of the intrinsic variability of ash composition, chemical analysis alone may not be representative of the whole ash-containing layer, thus limiting the identification of this material. By comparing the morphology, texture and composition of calcite pseudomorphs in laboratory ash to the ground preparations in three Baroque paintings, we provide additional, unequivocal tools to identify calcite particles from ashes in paint cross sections. The results demonstrate that the chemical composition of the ash can vary, but that the morphology and size of the calcite pseudomorph crystals abundantly present in the recycled ash applied to the canvas supports are consistent and extremely characteristic. The unique polygonal shapes and skeletal morphology of the pseudomorphs and their abundance make them ideal markers to recognize ash in paintings' ground layers, even when very limited amounts of sample are available. The study shows also that the practice of using recycled ash in the preparation of ground layers occurred outside Spain, by artists with direct or indirect Spanish lineage.