*3.2. Color and Color Stability*

Microfaedometry indicated that no color is alarmingly light-sensitive, or in any case more sensitive than the paper support (Figure 8). It is important to note that although the tonality of two colors might be similar, like for example Blue 1 and 2, their light sensitivity can be different as a result of their different composition. This highlights the importance of confirming the composition of all the gouaches across this work and other cut-outs by Matisse.

**Figure 8.** The light sensitivity of all colors represented in *Jazz* on a range from BW1 (most sensitive) to BW3 (moderate sensitivity).

The most sensitive colors appeared to be Blue 1, 4, and 5, Pink 2, and Orange 1. The light blue and pink colors in this group are more transparent. Consequently, the microfaedometry testing also reflects the light sensitivity of the paper support. Fading of Matisse's blue gouaches was reported in the past [11] for *The Swimming Pool* (1952) and linked to the acidic environment created by the burlap support [45]. Despite being a lightfast pigment [53], studies have shown that fading of this pigment can be promoted by the paint medium [55]. It appears, however, that the presence of white pigments and fillers in B2 and B3 increases the lightfastness of the gouaches. Orange 6 and the slightly less light-sensitive Orange 1 are the only gouaches that contain PR4, and their sensitivity was unexpectedly high considering the good lightfastness reported for PR4 in the literature (though they are reported to darken overexposure) [41]. Conversely, the sensitivity of Green 1 and to a lesser extent of Green 3, both richer in PG7 than the more light-stable Green 2, was also unexpected [41]. In contrast, although aniline (CV/MV) and xanthene dyes (rhodamines) have reputedly poor lightfastness [41,56], neither the magenta nor the violet gouaches were exceedingly light-sensitive.

The results of the microfaedometry testing led to new recommendations for the exhibition of the *Jazz* plates at MoMA. The prints have been grouped based on their vulnerability to color change and prioritized for upcoming displays depending on their exhibition history. Prints P14, P15, P16, and P20 are considered the most susceptible to fading as they contain at least two of the most vulnerable colors (BWeq = 2), while prints P6, P7, P10, P11, and P18 are slightly more stable but still contain three or more moderately sensitive colors (BWeq = 2.5).

#### **4. Conclusions**

The identification of the pigments present in the gouaches used by Henri Matisse was important to understand the current condition of the *Jazz* prints and support preventive conservation strategies. Based on the analysis carried out at MoMA and at the MNAM, a total of 39 distinct colored gouaches were used to reproduce the *Jazz* prints. Some of the colors, though similar in tonality, have a different composition which has implications for their light stability and display recommendations. The composition of the gouaches was consistent across the three copies of *Jazz* investigated and it is reasonable to assume that this applies to the rest of the existing copies since they were printed at the same time [6].

This study also illustrates the value and limitations and challenges of using a noninvasive approach that combines p-XRF, r-FTIR, and p-Raman to characterize the Linel gouaches used by Matisse in his cut-outs. More than twenty different pigments and extenders were detected and characterized across the twenty *Jazz* plates. All the pigments were identified using a non-invasive approach that combines p-XRF, r-FTIR, and p-Raman analysis with the exception of the methyl violet and/or crystal violet (MV/CV) and the Rhodamine 3B and 6G pigments that could only be identified by confocal Raman or SERS. The organic pigments PR3, PR4, PR49:2, PY3, PY5, PY6, and PY10 were identified by r-FTIR and p-Raman when present as major constituents, while PG7 was better identified by Raman. p-XRF was particularly suited to detect the presence of mineral pigments, especially when in low concentration, as it was the case of lead chromate and vermilion. It also hinted at the presence of the triarylcarbonium pigments (R3B and R6G) precipitated with complex ions (copper ferrocyanide or phosphotungstic acid). It was also helpful to confirm the presence of inorganic pigments and extenders identified by r-FTIR and/or p-Raman namely Prussian Blue, synthetic ultramarine, bone black, iron oxides, titanium white, barium sulfate and/or lithopone, calcium sulfate, and carbonate. While most of the colors were at least as light-stable as the paper background, adhering to lighting and exhibition guidelines for sensitive works on paper is important to sustain the vibrancy of the most sensitive colors and preserve the harmony and energy of the compositions so vital to Matisse.

Matisse was known to have used gouaches straight out of the tube and unmixed for his cut-outs [11], but the gouaches used in *Jazz* might have been made-to-order as Linel colorists worked closely with Matisse, Tériade, and Vairel to reproduce this large number of prints. Some of the gouaches have very similar tonalities but slightly different compositions, like the reds, some of the yellows and blues, as well as the blacks. This might have been deliberate to produce slight nuances across the plates or stemmed from the need to prepare multiple batches of gouaches. Although the gouaches identified in *Jazz* might have a unique composition, the analytical findings should still be relevant for the study of Matisse's cut-outs, including for dating and authentication purposes.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/heritage4040231/s1, Figure S1: p-XRF spectra for the Black 1 (Bk1) and Black 2 (Bk2), Figure S2: r- and μ-FTIR spectra of Black 1 (Bk1) and Black 2 (Bk2), Figure S3: Confocal and p-Raman spectra of Black 1 (Bk1) and Black 2 (Bk2), Figure S4: SERS spectra of Violet (V), Figure S5: p-XRF spectra for the Violet (V), Figure S6: Normal (confocal) Raman and SERS spectra of Magenta (M), Figure S7: p-XRF spectra for the Magenta (M), Figure S8: p-XRF spectra for the Pink 1 (Pk1) and Pink 2(Pk2), Figure S9: Confocal Raman spectrum of Pink 2 (Pk2), Figure S10: p-XRF spectra for the Blue 1 (B1), Blue 2 (B2) and Blue 3 (B3), Figure S11: r- and μ-FTIR spectra of Blue 2 (B2), Figure S12: Confocal and p-Raman spectra of Blue 2 (B2), Figure S13: Confocal and p-Raman spectra of Green 2 (G2), Figure S14: p-XRF spectra for the Green 1 (G1) and Green 3 (G3), Figure S15: r- and μ-FTIR spectra of Green 2 (G2), Figure S16: r- and μ-FTIR spectra of Yellow 5 (Y5), Figure S17: r- FTIR spectrum of Yellow 3 (Y3), Figure S18: Confocal and p-Raman spectra of Yellow 4 (Y4), Figure S19: Confocal and p-Raman spectra of Yellow 1 (Y1) and Yellow 2 (Y2), Figure S20: p-XRF spectra for the Yellow 1 (Y1), Yellow 4 (Y4) and Yellow 5 (Y5), Figure S21: Confocal Raman spectrum of Yellow 5 (Y5), Figure S22: p-XRF spectra for the Orange 4 (O4) and Orange 5 (O5), Figure S23: (a) Confocal Raman spectrum of Orange 5 (O5); confocal Raman spectrum of Orange 6 (O6); confocal and p-Raman spectrum of Gray 2 (Gy2), Figure S24: r- and μ-FTIR spectra of Orange 6 (O6), Figure S25: r- and μ-FTIR spectra of Orange 6 (O6), Figure S26: Confocal Raman spectrum of Orange 6 (O6), Figure S27: r- and μ-FTIR spectra of Red 4 (R4), Figure S28: Confocal Raman spectrum of Red 1 (R1), Figure S29: p-XRF spectra for the Red 1 (R1) and Red 2 (R2), Figure S30: p-XRF spectra for White 1 (W1) and White 2 (W2), Figure S31: p-XRF spectra for the Gray 1 (Gy1), Gray 2 (Gy2) and Gray 3 (Gy3), Table S1: All pigments and auxiliary compounds detected and identified across three copies of Jazz using a multi-analytical approach, Table S2: Gouaches identified in each Jazz plate.

**Author Contributions:** Conceptualization, A.M. and M.D.; Data curation, A.M.; Formal analysis, A.M., M.D., A.H., C.D., A.G.-L.B. and T.T.; Investigation, A.M. and A.C.P.; Methodology, A.M., A.C.P. and M.D.; Project administration, A.M. and M.D.; Resources, A.C.P.; Writing—original draft, A.M.; Writing—review & editing, A.C.P., M.D., A.H., C.D., A.G.-L.B. and T.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Fondation des Sciences du Patrimoine and the Cooperation and International Mobility 2018 program; National Science Foundation (CHE-1402750) and HRD-1547830 (IDEALS CREST); City University of New York PSC-CUNY Faculty Research Award Program, Grant No. 69079.

**Data Availability Statement:** Data available upon request to authors.

**Acknowledgments:** Martins, Prud'hom, Duranton, Daher, and Geanatche acknowledge the financial support of the Fondation des Sciences du Patrimoine and the Cooperation and International Mobility 2018 program, as well as the support from Veronique Serano-Stedman and Jonas Strove at the Musée National D'Art Moderne de Paris. Haddad is indebted to the National Science Foundation and the City University of New York. Tang acknowledges the MoMA Summer Internship Program. Martins is grateful for the support of MoMA colleagues Karl Buchberg, Laura Neufeld, and Jodi Hauptman. Martins would also like to thank Georges Matisse and the Matisse family for their generous support. The authors acknowledge the support of Federica Pozzi, Anna Cesaratto, Marco Leona, and The Network Initiative for Conservation Science (NICS) for lending the Bruker Bravo p-Raman instrument. The authors would like to thank Xavier Gallet, Matthieu Lebon and Olivier Tombret (UMR 7194 CNRS–Histoire Naturelle de l'Homme Préhistorique) for providing access their Elio portable XRF.

**Conflicts of Interest:** The authors declare no conflict of interest.
