2.1.2. Color Palette

Table 1 summarizes the main findings by FORS and XRF spectroscopic techniques of the materials composing the color palette. A detailed description of each pigment is also provided further in this section.

**Table 1.** Description of the palette by FORS and XRF spectroscopic techniques. <sup>a</sup> = absorption maximum, <sup>b</sup> = inflection point, <sup>c</sup> = reflectance maximum. A correspondence between FORS and XRF measurements as well as a detailed description of XRF results can be found in Appendix B Tables A1–A6.


*The gilding strategies:* In the *Purísima Concepción*, golden regions are present in Mary's apparel, her jewelry, in the *stellarium*, radiance, and in the *painting's frame*, with different shades and finishes. The interpretation of the XRF spectra (Figure 3) of the golden regions indicate the presence of Pb, Au, Cu, Fe, Ca, Sn, and As. These elements are, in turn, associated with the presence of various pictorial materials. For the gilding, a gold alloy, mainly composed of Au and Cu with a significant presence of Pb, commonly associated with lead white (2PbCO<sup>3</sup> Pb (OH)2), e.g., in the trimming, *stellarium*, crown, and frame. The presence of Fe is due to the use of brown layers for shadows. These two elements (Fe and Pb) are present in a higher proportion in the broad golden lights on the upper part of the painting. The spectra also present an associated signal of Sn, probably related to the tin lead yellow present in the jewelry highlights. The As signal and a noticeably intense

enhancement in the region where the S signal is expected provide evidence that orpiment (As2S3) could be present in the earrings and radiance of the Virgin Mary. ably intense enhancement in the region where the S signal is expected provide evidence that orpiment (As2S3) could be present in the earrings and radiance of the Virgin Mary. ably intense enhancement in the region where the S signal is expected provide evidence that orpiment (As2S3) could be present in the earrings and radiance of the Virgin Mary.

frame. The presence of Fe is due to the use of brown layers for shadows. These two elements (Fe and Pb) are present in a higher proportion in the broad golden lights on the upper part of the painting. The spectra also present an associated signal of Sn, probably related to the tin lead yellow present in the jewelry highlights. The As signal and a notice-

frame. The presence of Fe is due to the use of brown layers for shadows. These two elements (Fe and Pb) are present in a higher proportion in the broad golden lights on the upper part of the painting. The spectra also present an associated signal of Sn, probably related to the tin lead yellow present in the jewelry highlights. The As signal and a notice-

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**Figure 3.** Representative XRF spectrum of a golden region around the crown (XRF.30). See the Appendix A general diagram for details on the acquisition location. **Figure 3.** Representative XRF spectrum of a golden region around the crown (XRF.30). See the Appendix A general diagram for details on the acquisition location. **Figure 3.** Representative XRF spectrum of a golden region around the crown (XRF.30). See the Appendix A general diagram for details on the acquisition location.

Likewise, representative FORS spectra of the golden regions are presented in Figure 4, where their main characteristics correspond to inflection points between 535 nm and 590 nm. In metals such as gold, radiation absorption in the visible region is mainly due to processes that involve free electrons. Likewise, representative FORS spectra of the golden regions are presented in Figure 4, where their main characteristics correspond to inflection points between 535 nm and 590 nm. In metals such as gold, radiation absorption in the visible region is mainly due to processes that involve free electrons. Likewise, representative FORS spectra of the golden regions are presented in Figure 4, where their main characteristics correspond to inflection points between 535 nm and 590 nm. In metals such as gold, radiation absorption in the visible region is mainly due to processes that involve free electrons.

agram.

agram.

**Figure 4.** FORS representative spectra from golden regions. Inflection points between 535 nm and 590 nm are indicated. Spectra corresponding numbers are indicated in the Appendix A general di-**Figure 4.** FORS representative spectra from golden regions. Inflection points between 535 nm and 590 nm are indicated. Spectra corresponding numbers are indicated in the Appendix A general di-**Figure 4.** FORS representative spectra from golden regions. Inflection points between 535 nm and 590 nm are indicated. Spectra corresponding numbers are indicated in the Appendix A general diagram.

The gilding technique in this painting consisted of flakes ground to a powder, then mixed in oil. Lead white was used to increase the covering power and density of the pictorial layer. The earrings and radiance were made with orpiment, and due to its characteristic tone, saturation, and brightness which makes it look like a precious metal, as well as its ease of handling, plasticity and economy, it replaced the use of gold in certain areas. The gilding technique in this painting consisted of flakes ground to a powder, then mixed in oil. Lead white was used to increase the covering power and density of the pictorial layer. The earrings and radiance were made with orpiment, and due to its characteristic tone, saturation, and brightness which makes it look like a precious metal, as well as its ease of handling, plasticity and economy, it replaced the use of gold in certain areas. The gilding technique in this painting consisted of flakes ground to a powder, then mixed in oil. Lead white was used to increase the covering power and density of the pictorial layer. The earrings and radiance were made with orpiment, and due to its characteristic tone, saturation, and brightness which makes it look like a precious metal, as well as its ease of handling, plasticity and economy, it replaced the use of gold in certain areas.

In contrast, the simulated frame was created with a golden and matte surface applied with a flat brush, whereas organic figures such as shells and tendrils are highlighted by a brownish shade applied with a round brush. In Novo-Hispanic works from the second half of the 17th century, simulated frames were recurring resources used by artists [19] due to an economic limitation, as it was necessary to provide a frame for the works, and bespoke frameworks may have been out of budget, or perhaps the painting of a frame was used to dignify the artistic content. In contrast, the simulated frame was created with a golden and matte surface applied with a flat brush, whereas organic figures such as shells and tendrils are highlighted by a

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Gold, an incorruptible and shiny-looking material, has been related to the solar, the igneous, and the divine over time, in addition to its aesthetic and theological metaphors that have added to the notions of prestige and wealth of the precious metal with economic value [20]. The difference between the materials identified to produce the golden effect of the jewels and the Virgin's crown, radiance, and the frame accounts for the knowledge about their properties, their cost, and possibly their existence in the market. The *decorum*, ornament, and splendor as an object for the liturgy, shows in the gold dust applied in the frame and trimmings, a consideration of distinction of power, luxury, and the elite, entrusted to the master workshop. brownish shade applied with a round brush. In Novo-Hispanic works from the second half of the 17th century, simulated frames were recurring resources used by artists [19] due to an economic limitation, as it was necessary to provide a frame for the works, and bespoke frameworks may have been out of budget, or perhaps the painting of a frame was used to dignify the artistic content. Gold, an incorruptible and shiny-looking material, has been related to the solar, the igneous, and the divine over time, in addition to its aesthetic and theological metaphors that have added to the notions of prestige and wealth of the precious metal with economic value [20]. The difference between the materials identified to produce the golden effect of

*Shades of blue:* Blue tones are in the second hierarchy of this painting. Even though different shades are registered for the mantle of the Virgin, the cloth of the right angel, the celestial background of the Holy Spirit, and the insular sea in the background, our results by imaging techniques, and by XRF and FORS spectroscopic techniques, indicate the use of only two pigments (see Figure 5 for XRF results), and also provide their distribution throughout the painting. Spectroscopic elemental analysis revealed the use of a Cu rich pigment in the blue regions of the Virgin's mantle and the clothing of the right angel, which was identified as azurite-Cu3(CO3)2(OH)2-from its characteristic bands (646 nm, 1496 nm, 2289 nm and 2352 nm, see references [18,21]) in the FORS spectra (see Figure 6). In the region of the Holy Spirit, the absorption peaks in these spectra are between 645 nm and 707 nm, and the shift in absorption peaks could be related to bathochromic effect caused by the mixing of pigments. With precision, the 660 nm peak is reported as the main characteristic of indigo [21]. Regarding the blue hues, the material distinction between a mineral and lake-pigment was researched in paintings of Virgin Mary from the 16th and 17th centuries [22]. The predominant color in the mantles is azurite, and indigo for the backgrounds. In this case, the anonymous painter continues with this knowledge and significance, proposing not only a common solution, but also the knowledge of treatise, and the cost of these materials. the jewels and the Virgin's crown, radiance, and the frame accounts for the knowledge about their properties, their cost, and possibly their existence in the market. The *decorum*, ornament, and splendor as an object for the liturgy, shows in the gold dust applied in the frame and trimmings, a consideration of distinction of power, luxury, and the elite, entrusted to the master workshop. *Shades of blue:* Blue tones are in the second hierarchy of this painting. Even though different shades are registered for the mantle of the Virgin, the cloth of the right angel, the celestial background of the Holy Spirit, and the insular sea in the background, our results by imaging techniques, and by XRF and FORS spectroscopic techniques, indicate the use of only two pigments (see Figure 5 for XRF results), and also provide their distribution throughout the painting. Spectroscopic elemental analysis revealed the use of a Cu rich pigment in the blue regions of the Virgin's mantle and the clothing of the right angel, which was identified as azurite-Cu3(CO3)2(OH)2-from its characteristic bands (646 nm, 1496 nm, 2289 nm and 2352 nm, see references [18,21]) in the FORS spectra (see Figure 6). In the region of the Holy Spirit, the absorption peaks in these spectra are between 645 nm and 707 nm, and the shift in absorption peaks could be related to bathochromic effect caused by the mixing of pigments. With precision, the 660 nm peak is reported as the main characteristic of indigo [21]. Regarding the blue hues, the material distinction between a

*Traces of mercury for red areas:* XRF spectra from the red areas revealed the use of a Hg rich pigment (Figure 7). Likewise, FORS reflectance spectra from these red areas show an inflection point around 594 nm as the main characteristic (Figure 8), confirming the presence of vermillion (HgS) as the main pigment to give this hue. Additionally, absorption characteristics were identified at 1198 nm and 1447 nm, associated with the first overtone of the hydroxyl group [2νOH] in the lead white pigment, as reported in Picollo et al. [23]. mineral and lake-pigment was researched in paintings of Virgin Mary from the 16th and 17th centuries [22]. The predominant color in the mantles is azurite, and indigo for the backgrounds. In this case, the anonymous painter continues with this knowledge and significance, proposing not only a common solution, but also the knowledge of treatise, and the cost of these materials.

**Figure 5.** (**a**) representative spectrum (XRF.24) from Holy Spirit region, (**b**) representative spectrum (XRF.55) from Virgin's mantle region. Their corresponding locations are detailed in Appendix A general diagram. **Figure 5.** (**a**) representative spectrum (XRF.24) from Holy Spirit region, (**b**) representative spectrum (XRF.55) from Virgin's mantle region. Their corresponding locations are detailed in Appendix A general diagram.

*Green tones:* A single pigment was identified in all the green areas from this painting, found in the representation of emeralds in the imperial crown, and the stems and leaves of the palm and the lily in the lower area. FORS spectra for this pigment have a reflectance maximum between 554 nm and 584 nm, and absorption bands between 696 nm and 717 nm (Figure 9), which together with the IR signature (Figure 10) allowed to identify the pigment as copper resinate [7]. XRF spectra (Figure 11) confirm the presence of Cu in the green areas, but also presents Pb, Hg and Fe, and vermilion or iron earth to change the saturation of the jewel and the volume from the shadows. Finally, the presence of Au in the green emeralds from the crown may indicate that these were painted over the golden region. *Heritage* **2021**, *4* FOR PEER REVIEW 9 Reflectance (norm)660 nm 483 nm 645 nm 1003 nm 514 nm 687 nm 917 nm

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660 nm

562 nm

508 nm

465 nm

722 nm

715 nm

1000 nm

1445 nm

1496 nm

1725 nm

1751 nm

1939 nm

2304 nm 2346 nm

Azurite

2289 nm

2352 nm

Holy Spirit

Indigo

Cu resinate

Virgin's Mantle

Angel

**Figure 6.** FORS spectra from blue regions: Virgin's mantle, angel's mantle, and Holy Spirit blue background. Vis-NIR reflectance features are indicated. Reference materials (indigo, Cu resinate, and azurite) are included for comparison. **Figure 6.** FORS spectra from blue regions: Virgin's mantle, angel's mantle, and Holy Spirit blue background. Vis-NIR reflectance features are indicated. Reference materials (indigo, Cu resinate, and azurite) are included for comparison. tone of the hydroxyl group [2νOH] in the lead white pigment, as reported in Picollo et al. [23].

[23].

Intensity

2 4 6 8 10 12 14 16 18 20 22 24 10 K Ar K Al K Mo (scatter) Lγ Pb **Figure 7.** Representative spectrum (XRF.73) from red regions. Features related with Hg are indicated. Spectra detailed location can be seen in Appendix A general diagram.

**Figure 7.** Representative spectrum (XRF.73) from red regions. Features related with Hg

are indicated. Spectra detailed location can be seen in Appendix A general diagram.

are indicated. Spectra detailed location can be seen in Appendix A general diagram.

Energy (keV)

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594 nm

 007 010

017

1198 nm

1447 nm

**Figure 8. (TOP)** FORS representative spectra from red regions (FORS.007 and FORS.010), inflection point near 594 nm related with vermilion (HgS) is indicated. **(BOTTOM)** (FORS representative spectra from incarnation regions (FORS.017 and FORS.021). Features near 1198 nm and 1447 nm, related with lead white are indicated. Spectra corresponding locations are indicated in Appendix A general diagram. **Figure 8. (TOP)** FORS representative spectra from red regions (FORS.007 and FORS.010), inflection point near 594 nm related with vermilion (HgS) is indicated. **(BOTTOM)** (FORS representative spectra from incarnation regions (FORS.017 and FORS.021). Features near 1198 nm and 1447 nm, related with lead white are indicated. Spectra corresponding locations are indicated in Appendix A general diagram. pigment as copper resinate [7]. XRF spectra (Figure 11) confirm the presence of Cu in the green areas, but also presents Pb, Hg and Fe, and vermilion or iron earth to change the saturation of the jewel and the volume from the shadows. Finally, the presence of Au in the green emeralds from the crown may indicate that these were painted over the golden region.

0.3

0.2 Reflectance (norm)**Figure 9.** FORS representative spectra from green regions. Reflectance maxima were observed between 554 nm and 584 nm, and absorption bands between 696 nm and 717 nm. Copper resinate reflectance spectrum was included for comparison. Numbers corresponding to spectra are shown in Appendix A general diagram.

400 600 800 1000 1200 0.0 0.1 Wavelength (nm) 562 nm 717 nm *Brown:* Brown areas in the painting were associated with the presence of Fe, as determined by XRF, possibly related with the use of burnt earth for the shadows, and are of a uniform hue. Its use in the hair and pupils of Mary and the angels were defined by brushstrokes at the tip of a round and fine brush, whereas for the volume of the cloths, the jewelry, or the crown, a flat brush was applied. From the interpretation by XRF spectroscopy, the abundant presence of Pb indicates the incorporation of white lead in this color layer, probably to provide a greater covering power.

*Flesh tones:* To generate the flesh tones of *Mary* and the angels, XRF identified the incorporation in a higher proportion of white lead (Pb), vermilion (Hg), azurite (Cu), and calcine natural iron oxide (Fe) (Figure 12). This mixture was made on a palette and applied with a fine brush tip. Vermilion was used for the touches of blush on the cheeks, whereas the volume of the face from lights used an abundance of lead white, and the shadows used natural sienna. **Figure 9.** FORS representative spectra from green regions. Reflectance maxima were observed between 554 nm and 584 nm, and absorption bands between 696 nm and 717 nm. Copper resinate reflectance spectrum was included for comparison. Numbers corresponding to spectra are shown in Appendix A general diagram. *Heritage* **2021**, *4* FOR PEER REVIEW 11 **Figure 9.** FORS representative spectra from green regions. Reflectance maxima were observed between 554 nm and 584 nm, and absorption bands between 696 nm and 717 nm. Copper resinate reflectance spectrum was included for comparison. Numbers corresponding to spectra are shown in Appendix A general diagram.

Wavelength (nm)

Lα Pb

Kα Cu

Kα Fe

Kα Ca

Intensity

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**Figure 10.** FORS spectra from green regions. Spectral features are indicated and compared with copper resinate reference. Spectra numbers of corresponding regions are shown in Appendix A general diagram. **Figure 10.** FORS spectra from green regions. Spectral features are indicated and compared with copper resinate reference. Spectra numbers of corresponding regions are shown in Appendix A general diagram. **Figure 10.** FORS spectra from green regions. Spectral features are indicated and compared with copper resinate reference. Spectra numbers of corresponding regions are shown in Appendix A general diagram.

### *Brown:* Brown areas in the painting were associated with the presence of Fe, as determined by XRF, possibly related with the use of burnt earth for the shadows, and are of *Brown:* Brown areas in the painting were associated with the presence of Fe, as de-*2.2. The Virgin Mary: Changes of View and Composition by Imaging Techniques*

**Figure 11.** Representative spectrum (XRF.029) from green regions, features related with Ca, Fe, and

calcine natural iron oxide (Fe) (Figure 12). This mixture was made on a palette and applied

calcine natural iron oxide (Fe) (Figure 12). This mixture was made on a palette and applied

a uniform hue. Its use in the hair and pupils of Mary and the angels were defined by brushstrokes at the tip of a round and fine brush, whereas for the volume of the cloths, the jewelry, or the crown, a flat brush was applied. From the interpretation by XRF spectroscopy, the abundant presence of Pb indicates the incorporation of white lead in this color layer, probably to provide a greater covering power. *Flesh tones:* To generate the flesh tones of *Mary* and the angels, XRF identified the incorporation in a higher proportion of white lead (Pb), vermilion (Hg), azurite (Cu), and termined by XRF, possibly related with the use of burnt earth for the shadows, and are of a uniform hue. Its use in the hair and pupils of Mary and the angels were defined by brushstrokes at the tip of a round and fine brush, whereas for the volume of the cloths, the jewelry, or the crown, a flat brush was applied. From the interpretation by XRF spectroscopy, the abundant presence of Pb indicates the incorporation of white lead in this color layer, probably to provide a greater covering power. *Flesh tones:* To generate the flesh tones of *Mary* and the angels, XRF identified the incorporation in a higher proportion of white lead (Pb), vermilion (Hg), azurite (Cu), and The comparison of the resulting images from the different techniques allowed the identification of changes in the Virgin Mary, the angels, and the iconographic elements that accompany them, and made it possible to identify restoration areas more easily in the artwork, which were not noticeable due to the yellowish varnish and the absence of documentation on the restoration carried out in the painting. Table 2 gathers the characteristics observed from the different imaging techniques for the three areas analyzed (Figures 13–16), where visible image, IRPC, UV image, and PC stand out.

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natural sienna.

**Figure 12.** Representative spectrum (XRF.041) from flesh tones, features related with Ca, Fe, Cu, and Hg are indicated, associated with the use of vermilion. Spectrum corresponding location is indicated in Appendix A general diagram. **Figure 12.** Representative spectrum (XRF.041) from flesh tones, features related with Ca, Fe, Cu, and Hg are indicated, associated with the use of vermilion. Spectrum corresponding location is indicated in Appendix A general diagram. *Heritage* **2021**, *4* FOR PEER REVIEW 13

with a fine brush tip. Vermilion was used for the touches of blush on the cheeks, whereas the volume of the face from lights used an abundance of lead white, and the shadows used

**Figure 13.** Virgin Mary face region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC9. **Figure 13.** Virgin Mary face region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC9.


**Table 2.** Results from imaging analysis for the three studied regions in the *Purísima Concepción*.

**Figure 14.** Virgin Mary's hands region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC8. **Figure 14.** Virgin Mary's hands region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC8.

**Figure 15.** Imperial crown and Holy Spirit region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM

image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC4.

**Figure 15.** *Cont.*

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**Figure 15.** Imperial crown and Holy Spirit region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC4. **Figure 15.** Imperial crown and Holy Spirit region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC4.

**Figure 16.** *Cont.*

**3. Conclusions** 

of the painting).

fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC8.

**Figure 16.** Right-side angel region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV

This work provided detailed information on the material composition of the color palette, by means of a combined imaging and spectroscopy method. HSI analysis has proven to be a powerful tool, and it allowed us to describe details on the distribution of the pigments, as well as a description on the manufacture of the painting. It also provided information on the presence of later repairs (consistent with UV imaging analysis), as well as insights on the existence of a previous painting (as was demonstrated by radiography

In this artwork, the selection of materials by the artist considered the importance of the represented objects. Golden regions are present with different shades and finishes, and a gold alloy was used for the trimming, stellarium, crown, and frame. Fe was used for brown layers in the shadows. Tin lead yellow is present in jewelry highlights, orpiment in the earrings, and in radiance of the Virgin Mary. Blue tones characterization indicates the use of only two pigments: azurite for the Virgin's mantle and the clothing of the right angel; and indigo for the Holy Spirit region. A single green pigment was found in the painting, located in the representation of emeralds, and the stems and leaves in the palm

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**Figure 16.** Right-side angel region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC8. **Figure 16.** Right-side angel region: (**a**) visible image; (**b**) pseudo color image; (**c**) SAM image; (**d**) UV fluorescence image; (**e**) RGB–PCA; (**f**) PC1; (**g**) PC2; (**h**) PC3; and (**i**) PC8.
