*3.3. Paper*

If documented in watermark databases, watermarks can provide information about the date and location of the paper production. Computed watermark images show that Plates 9 and 55 share a watermark in the shape of a bishop or abbot, wearing a mitre and a cross, bearing a staff and banner (Figure 12). The dark shadow around vertical chain lines indicates that the paper is antique laid paper, rather than laid or wove, suggesting that it was produced before the end of the eighteenth century [48].

**Figure 12.** Computed images of watermarks found in plate 55 (**top left**), plate 9 (**top middle**) and plate 54 (**bottom**). The outline of a bishop watermark can be observed when manually reinforced in plate 9 (**top right**).

Dating of the watermarks themselves was inconclusive. This particular bishop watermark has not been documented in any of the common databases of eighteenth century watermarks, and does not match with watermarks in other editions of *Metamorphosis*, given in Figure 13.

**Figure 13.** Transmitted light images showing watermarks in different editions of *Metamorphosis*. 1705 (not shown) and 1726 (**left**) editions both share the Strasbourg Lily watermark. The 1705 countermark is "PVL" (not shown) the 1726 countermark is "Honig" (**middle**). The 1771 edition has an unidentified watermark (**right**) and unintelligible countermark with text.

Watermarks are helpful, however, in addressing whether sheets were produced and procured from the same maker or edition. Plates 9 and 55 have the same watermark; however, the prints were impressed on the opposite side of the sheet with the watermarks vertically inverted with respect to one another. This suggests that these two sheets come

from the same batch of paper and are likely mold-mates. This supports the hypothesis that plates 9 and 55 came from the same original source.

#### **4. Conclusions**

This paper has presented the technical analysis of three prints from *Metamorphosis Insectorum Surinamensium* by Maria Sibylla Merian in Northwestern University Library's Special Collections. The analysis was undertaken in order to determine a date, printer, and colorist for the prints, which were difficult to ascertain due to the complexities of the timeline of publication of Merian's works and the common practice of later coloring of early modern prints. This study employed a holistic analysis that would facilitate the non-invasive characterization of the artworks in three layers: pigment, print, and paper. Because of similarities in pigments—brown umber, barium-rich red, cadmium red, and lithopone—used in multiple plates, similar characteristic spectra for green pigments in all three plates, and the matching watermarks in plates 9 and 55 we conclude that the prints belonged to the same edition and were colored together. The use of two different red pigments, one barium-rich and the other cadmium red, and two different white pigments, titanium white and lithopone, alludes to the possibility of multiple campaigns of coloring, but this remains an open question. We date the coloring to post-1920, based on the use of cadmium red and titanium white, which were not commercially available to artists before 1919 and 1920, respectively. Based on the presence of features that are only present in posthumous editions of Merian's plates as they were reprinted in later editions, namely a Roman numeral plate number and French caption, we date the prints themselves to a French translation published in Paris in 1771. A more specific dating of the printed elements or the painted components would require further analysis of the organic components of the drawing and further research into the provenance of the watermarks.

The relative chronology of the different components of the prints in Northwestern Special Collections confirms that the prints are the product of a twentieth century art dealer or collector adding coloration to earlier prints. The dating of the coloring as well as the care with which it was undertaken suggest that this may have been an attempt to add value to relatively low-value later editions of Merian's works. As a result of this study the prints will be re-cataloged in the Northwestern Library catalog and the use of these prints by students and researchers will therefore be better contextualized in terms of this more complicated provenance.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/heritage4030088/s1, Figure S1: Elemental maps resulting from MA-XRF scan of plate 9, Table S2: Results of XRF point analysis for plate 9, Figure S2: Sample locations for XRF point analysis of plate 9, Figure S3: Endmember maps resulting from hyperspsectral imaging for plate 9 and associated reflectance spectra, Figure S4: Elemental maps resulting from MA-XRF scan of plate 54, Table S3: Results of XRF point analysis for plate 54, Figure S5: Sample locations for XRF point analysis of plate 54, Figure S6: Endmember maps resulting from hyperspectral imaging for plate 54 and associated reflectance spectra, Figure S7: Elemental maps resulting from MA-XRF scan of plate 55, Table S4: Results of XRF point analysis for plate 55, Figure S8: Sample locations for XRF point analysis of plate 55, Figure S9: Endmember maps resulting from hyperspsectral imaging for plate 55 and associated reflectance spectra.

**Author Contributions:** Conceptualization, O.D., M.V., A.M., M.W.; methodology, O.D., M.V., A.M., M.W.; investigation, O.D., M.V., A.M.; data curation, O.D., M.V., A.M.; writing—original draft preparation, O.D.; writing—review and editing, O.D., M.V., AM., M.W.; visualization, O.D., M.V.; supervision, M.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This collaborative initiative is part of NU-ACCESS's broad portfolio of activities, made possible by generous support of the Andrew W. Mellon Foundation.

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Data Availability Statement:** Data supporting this study are available in the associated supplementary information file.

**Acknowledgments:** The authors gratefully acknowledge support from and collaboration with Northwestern University Libraries Charles Deering McCormick Library of Special Collections Curator Scott Krafft and Northwestern University Libraries Book and Paper Conservator Roger Shaw. The authors wish to thank Katie Lattal, Special Collections Librarian at Galter Health Sciences Library and Learning Center, for facilitating access to Galter Library holdings.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

## **Appendix A. Proposed Pigment Identifications and Corresponding Elements**

**Table A1.** Summary of elements present in XRF analysis for plate 9.


**Table A2.** Summary of elements present in XRF analysis for plate 54.


**Table A3.** Summary of elements present in XRF analysis for plate 55.

