*Article* **Multi-Modal, Non-Invasive Investigation of Modern Colorants on Three Early Modern Prints by Maria Sibylla Merian**

**Olivia Dill, Marc Vermeulen, Alicia McGeachy and Marc Walton \***

The Center for Scientific Studies in the Arts (NU-ACCESS), Northwestern University, Evanston, IL 60208, USA; oliviadill2024@u.northwestern.edu (O.D.); marc.vermeulen@northwestern.edu (M.V.); alicia-mcgeachy@northwestern.edu (A.M.)

**\*** Correspondence: marc.walton@northwestern.edu

**Abstract:** Northwestern University's Charles Deering McCormick Library of Special Collections owns three hand-colored copperplate engravings that once belonged to an edition of *Matamorphosis Insectorum Surinamensium* by artist-naturalist Maria Sibylla Merian (1647–1717). Because early modern prints are often colored by early modern readers, or modern collectors, it was initially unclear whether the coloring on these prints should be attributed to the print maker, to subsequent owners or collectors, or to an art dealer. Such ambiguities posed challenges for the interpretation of these prints by art historians. Therefore, the prints underwent multi-modal, non-invasive technical analysis to assess the date and material composition of the prints' coloring. The work combined several different non-invasive analytical techniques: hyperspectral imaging (HSI), macro X-ray fluorescence (MA-XRF) mapping, surface normal mapping with photometric stereo, visible light photography, and visual comparative art historical analysis. As a result, the prints and paper were attributed to a late eighteenth-century posthumous edition of Merian's work while the colorants were dated to the early twentieth century. This information enables more thorough contextualization of these prints in their use as teaching and research tools in the University collection.

**Keywords:** Maria Sibylla Merian; colored prints; hyperspectral imaging; X-ray fluorescence spectroscopy; photometric stereo; Prussian blue; non-invasive pigment characterization
