Caravaggio's copper

St. John the Baptist in the Wilderness, commissioned for the private chapel of Genoese banker. Ottavio Costa in 1602/3 and now in the collection of the Nelson‐Atkins Museum of Art (#52‐25), provides an important opportunity to understand Caravaggio's use of materials from one of his best‐preserved paintings. macro‐X‐ray fluorescence (MA‐XRF) elemental mapping has now been used to build upon a 2016 stratigraphic study of the palette employing optical and UV fluorescence microscopies, scanning electron microscopy‐energy dispersive X‐ray spectrometry (SEM‐EDS), Raman spectroscopy, and polarized light microscopy. The combined results of these methods clarify aspects of the iconography that have previously been obscure and expand our understanding of the roles of the various pigments. The roles for copper‐based pigments are surprisingly diverse for a painting with few obvious green and blue passages, in which many greens are based on terraverte. Darkening of the foliage adjacent to the figure of St. John has long posed interpretive difficulties, due to poor legibility of the plants depicted there. The foliage has been clarified by the results of MA‐XRF mapping, which distinguish the plant species by the palette choices involved in their depiction. Copper pigments play a fundamental role in Caravaggio's work, shading and modulating complementary colors with the additional practical benefit of playing a siccative role in paints that would otherwise dry poorly. MA‐XRF mapping has also revealed a role for copper pigment used to lay out the composition that was not apparent through radiography or infrared imaging methods.