A study of the origin and gilding technique of a Hispano-Philippine ivory from the XVIIth century

Journal of Archaeological Science: Reports 4 (2015) 1–7

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Journal of Archaeological Science: Reports

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A study of the origin and gilding technique of a Hispano-Philippine ivoryfrom the XVIIth century

M. Rozalen a,⁎, A. Ruiz Gutierrez b

a Instituto Andaluz de Ciencias de la Tierra, IACT (CSIC-UGR) Avda. de las Palmeras 4, 18100 Armilla, Granada, Spainb Departamento de Historia del Arte, University of Granada, Campus Universitario de Cartuja, s/n, 18071 Granada, Spain

⁎ Corresponding author.E-mail address: [email protected] (M. Rozalen).

http://dx.doi.org/10.1016/j.jasrep.2015.08.0342352-409X/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

Article history:Received 25 April 2015Received in revised form 23 July 2015Accepted 22 August 2015Available online xxxx

Keywords:Hispano-PhilippineIvoryMicrostructureFTIRSEMPolychromeHydroxyapatite

This paper reports on the multidisciplinary (historic-scientific) study of a Hispano-Philippine image of theImmaculate Conception from the XVIIth century, whose remains are preserved in the local parish of Íllora(Spain). FTIR spectroscopy was used to determine the origin of the sculpture's primary material, which helpsus to know the circulation and commercial routes of ivory during themodern age. Comparative resultswith a cer-tified African ivory reference sample indicate the Asian origin of our image. Historically, our results support theidea that Asian tusk ivory from India and South-East Asia were commonly carved by artisans in the area ofZhanzhou Port (Fujian province), and consequently by the same artisans when they settled in Manila.Scanning electron microscopy was used to determine the materials and gilding techniques used in this type ofsculpture. This is a new aspect for Hispano-Philippine ivories, but a recurrent one formedieval ivories. The resultsobtained in this study allow us to present the gilding technique used to decorate the Immaculate Conceptionimage as a water gilding (“guazzo”) over an oil/mordant gilding. Water gilding uses a layer of gesso and alayer of bole to make the gold leaf adhere, and was traditionally used for wood surfaces, but has also been doc-umented in the cases of some medieval ivory sculptures.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Art research for sculpted ivory is generally done through the obser-vation of the piece by an expert. Dating is not always possible if there isno documentation for the image.

Chemical and structural analyses of these pieces through analyt-ical studies could provide valuable information regarding the authentic-ity, alteration, and identification of the pigments used in the case ofpolychromed images. Moreover, some of these techniques, such asFourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy,or Scanning Electronic Microscopy (SEM) require minimum sampling,and are suitable for any well-equipped analytical or conservation labo-ratory. Multidisciplinary work between environmentalists, geochem-ists, archaeologists, and art historians is the key to resolving hot topicson ivory research.

The use of spectroscopic methods in the analysis of hard animaltissues is not new. FTIR, Raman, and Ultraviolet Fluorescence Spectrom-etry have all been used to investigate elephant ivories in the past(Edwards and Farwell, 1995, Edwards et al., 1998, Banergee, 2008a,Banerjee, 2008b). The distinction between African and Asian elephant

tusk is possible thanks to the studies of Banerjee et al. (2008a, 2008b),which used quantitative measurements of the phosphate bands. Re-cently, a study by Turner-Walker and Xu (2014) has developed a newmethod consisting of quantitative measurements made onmultiple ad-sorptions in order to distinguish different species of ivory.

There are some studies in the literature that use techniques suchScanning Electron Microscopy (SEM) to analyse the damage to somemuseum images and fossil ivories (e.g. Roger et al., 2005; Singh et al.,2006).

Most of these ivory images are sculpted out of elephant teeth, whosephysical structure is composed of the pulp cavity, dentine, cement, andenamel. The inner part consists of the pulp cavity, and an empty spaceinside the tooth. Odontoblasts are aligned in the pulp cavity, and are re-sponsible for the production of dentine. Dentine is the mayor compo-nent of ivory images, and forms a layer with a consistent thicknessaround the pulp cavity.

Dentine is a mineralized connective tissue with an organicmatrix of collagen proteins. The inorganic compound of dentineis called carbonate-hydroxyapatite, whose chemical formula isCa10(PO4)6(CO3)H2O. Dentine contains microscopic structures calleddentine tubules, which are small channels radiating outward fromthe pulp cavity to the outer border where the cement is. These chan-nels have different configurations, and depending on the type ofivory, their diameter is between 0.8 and 2.2 μm (Yin et al., 2013).

Fig. 1. Immaculate Conception image located at “Nuestra Señora de la Encarnación” parishin Íllora (Granada, Spain).

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1.1. Aim of the study

The main objectives of this study are:

1. To determine the origin of the primary material of the sculpture,African or Asian ivory.

2. To observe this sculpture's microstructure and degree of alterationusing SEM. Moreover, we propose to identify and determine thecomposition of different substances used in the gilding of the imagewith the aim of extrapolating these results to other images, helpingart historians to clarify key points that could not be determineddue to the lack of documentation.

2. Material

2.1. The historical context of the studied image

Ivory has been carved to produce luxury artistic objects since an-cient times, but to analyse the image in this study, we have to focuson the South of China, specifically on Zhanzhou Port, province of Fujian(Mcarthur, 2005).

The presence of the Spanish in the Philippine archipelago from 1565to 1895 started with the process of evangelisation. They foundedparishes, and brought liturgical ornaments from Spain. Chinese artisansfrom Zhanzhou saw that the demand generated a business opportunity,and settled in Manila in 1590. They started to carve images in theEuropean style using ivory as raw material, because it was easy tocarve, and it had been an integral part of their artistic culture since pre-historic times. Called “Sangleyes,” these Chinese artisans started toteach Filipino artisans starting at the end of the XVIIth century, and con-tinued until the XIX century, which is clearly visible in the progressiveoriental facial features of these images (Ruiz Gutiérrez, 2013).

The image analysed in this study represents this Hispano-Philippineivory school, existing between the XVIIth and XIXth centuries, whichwas related to the Spanish presence in the archipelago, andwas encour-aged by the presence of Chinese artisans in Manila. These images wentback to Spain thanks to the establishment of the Manila Galleons(1565–1815) though the Viceroyalty of New Spain. The leading ivorycollections are currently preserved in the countries involved in thistrans-Pacific route (the Philippines, Mexico, and Spain), which beganthe process of artistic globalisation.

The discovery of this fragmented image of the Immaculate Concep-tion, located at “Nuestra Señora de la Encarnación” church in Íllora(Granada, Spain, Fig. 1), has been fundamental to starting an, as yet,unique scientific–historical study.

The image is dressed in a tunic that reaches her feet, tied at thewaist,and in a robe that is gathered over her left arm. It is raised upon a base oforiental clouds. Curly hair, separated in sections, is insinuated. Althoughno facial fragments have been found, sculptures that are similar in chro-nology and iconography (Fig. 2) show images with oriental features,such as rippled eyelids, long earlobes, and a double chin. Moreover,the hair layout and shoes are typical of these oriental sculptures.Both images are also of a similar size (Fig. 2 is 47 cm high, and Fig. 1 is42 cm high without the head).

Lush vegetable decoration, formed by small symmetrical bouquets,is of significant relevance, since this was commonplace during theXVIIIth century. Consequently, this image probably dates from aroundthe endof the XVIIth century. Thiswas confirmedby the documentationfound at the church of “Nuestra Señora de la Encarnación,” and iden-tifies the benefactor as D. Juan de Osorio Crespo, secretary of the HolyOffice of the Inquisition in Mexico around 1700 (Verdejo Martín,2006). Unfortunately, this piece has suffered throughout its history, be-cause it was buried during the Spanish CivilWar to avoid spoliation, andwas accidentally broken when it was recovered during an excavation inthe seventies. This fact let us to take samples from representative parts,and to study the decoration in detail.

2.2. Sample collection for scientific analysis

Overall, we took 4 samples, around 1–2 mg each, manually drillingdifferent parts (Fig. 3), and taking care to avoid any damage to theimage. Sample 1 (mvi-1) was collected from the inner zone of thetusk, which is 42 cm long (Fig. 3b). The sampling area corresponds todentine. Its study will give an idea of its composition, and will let usobserve the microstructure and general alteration of the image. Sample2 (mvi-2) was collected from the base of the image, and correspondsto the most altered part (Fig. 3c). Samples 3 (mvi-3) and 4 (mvi-4),(Fig. 3d), correspond to coloured parts, and were collected from thebase to avoid any damage to the frontal part of the tusk.

3. Analytical methods

3.1. FTIR spectroscopy

Infrared spectroscopy deals with the vibration of the bonds betweena substance's molecules under infrared light. The FTIR spectrum of anivory sample consists of absorption bands created by the vibrations ofmolecules of collagen, carbonate, and phosphate from hydroxyapatite(also called dahlite), and bands of OH andH2O. This leads to a character-istic outline (spectrum) that allows us to determine the origin and alter-ation of the sample.

FTIR spectra were recorded in absorbance mode in the4000–400 cm−1 range using a PerkinElmer SpectrumOne spectrometerwith a spectral resolution of 4 cm−1 from the average of 100 spectra.Samples were prepared in pressed KBr pellets by diluting 1 mg of thesample in 100 mg of dried KBr. The pellets were heated overnight at110 °C before analysis. Grams/32 (Thermo Fisher Scientific Inc., 2011)

Fig. 2. Immaculate Conception (XVIIth century) Private Collection (México). PhotographicArchive of Institute for Aesthetic Research of the UNAM.

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software was used to plot and analyse the spectra. The FTIR spectra ofthe samples were evaluated by comparing them with the standardspectrum of a documented sample of Loxodonta africana donated by ataxidermist. In the spectra, the absorbance was normalised against the

Fig. 3. Ivory samples collected from a broken Immaculate Conception image located in the churc) broken piece from the base of the image. Sample mvi-2 was collected from a much altered(brown) were collected to study their polychrome.

more intense band (1032 cm−1) in order to compare changes in the in-tensity of the bands between both samples.

3.2. scanning electron microscopy

Changes in particle morphology were observed using a LEO Gemini153 Field Emission Scanning Electron Microscope (FESEM), operatingat 1–2 kV, and at a working distance of 2 mm. The microscope waslinked to an Energy Dispersive X-ray Spectrometer (EDS, OxfordINCA200),whereby specific analyses of selectedpolychromed or alteredzones can be performed. This informationwill help evaluate the conser-vation state of the sample, and will give information about the decora-tion process of these images.

Fine powder from every sample (mvi-1, mvi-2, mvi-3 and mvi-4)was scattered into a holder coveredwith double-coated conductive car-bon tape, and then coated with a layer of carbon to make it conductive.Moreover, one of the samples (mvi-4) was embedded in an epoxy resin.The coloured part was oriented by cross-section, and embedded againinto a round epoxy resin. Finally, it was polished with diamond paste,and carbon coated before SEM observation.

4. Results and discussion

4.1. Origin

The physical and chemical properties of ivory depend on the size ofthe carbonate-hydroxyapatite crystals and the state of conservation ofthe collagen. These two factors are different in Asian and in Africanivory, for example, dahlite crystals in Asian ivory are smaller thanthose in African ivory. Consequently, the absorption bands, due to thevibration of the carbonate and phosphate molecules in the FTIR spec-trum of Asian ivory, are different than those in the FTIR spectrum ofAfrican ivory. For this reason, Asian ivory can be distinguished by ob-serving the shapes and intensities of the peaks in the region between1500 and 500 cm−1 in the spectra (Nocete et al., 2013).

Fig. 4 shows the FTIR spectra obtained for the L. africana sample(Fig. 4b) and our image (Fig. 4a). Both spectra present a similar outline,but some differences can be observed.

ch of Illora. a) Set of pieces that form the image. b) Inside part of the tusk (sample mvi-1), brown-coloured part. d) Detail for the base where samples mvi-3 (golden) and mvi-4

Fig. 5. a) Typical morphology of dentine. White arrows show dentine tubules parallel tothe longitudinal axis of the sample. b) Detail of dentine tubules. One of the arrows indi-cates the platy hydroxyapatite crystals. The other arrow points out to two spherical parti-cles corresponding to two spores.

Fig. 4. a) FTIR spectrum of the Inmmaculate Conception image. Characteristic smooth slope at 1088 cm-1 and shape of 1033cm-1 bandmatch with the spectrum obtained in Nocete et al.(2013) for Elephas maximus (Asian Elephant). b) FTIR spectrum of an African (Loxodonta africana) sample. In this case the band around 1033cm-1 presents a shoulder near 1096 cm-1 char-acteristic of African ivory.

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A common broad band around 3434 cm−1 appears in both spectra,and it is caused by hydroxyl stretching vibration. Two bands at 2924and 2853 cm−1 correspond to asymmetric and symmetric stretching vi-brations of the CO3

2− group of collagen (Qi et al., 2005).Two strong absorption peaks at 1660 and 1548 cm−1 are caused by

the bending vibration of coordinated water, or the twisting of H–O–H,and are clearly visible for the L. africana sample spectrum (Fig. 4b).However, our image's spectrum (Fig. 4a) shows lower intensity absorp-tion, especially for the band at 1548 cm−1, indicatingmuch lowerwatercontent (Zhou et al., 1999), which is typical for archaeological samplesburied for long periods of time.

The biogenic hydroxyapatites have three absorption peaks, at 1548,1455, and 1415 cm−1 (Huang et al., 2007) that are visible in both spec-tra. Moreover, the maximum band appears at 1032 cm−1, caused byasymmetric stretching vibration of the PO4

3− (the major constituentbeinghydroxyapatite). However, for the L. africana spectrum, a shouldernear 1096 cm−1, corresponding to the vibration of CO3

2− on PO43−

groups, identifies the African origin of this sample (Nocete et al.,2013). In our image's spectrum, this shoulder appears only as a smoothslope in the same region, which is typical for Asian elephant samples(Shuhmacher and Banerjee, 2012, Nocete et al., 2013).

The experimental evidence of the Asiatic origin of the tusk usedto carve this image is fundamental to thefield of art history, and precise-ly to the ambit of Hispano-Philippine ivory. Historically, both sources,African and Asiatic, are suitable. On one hand, the flow of African ivorytusks arrived in China and the Philippines via Arabmerchants, as report-ed by Yepes (1996), or recently by Regalado and Villegas (2004). On theother hand, our results support the idea that Asian ivory from India andSouth-East Asia, was commonly carved by the artisans in the area ofZhanzhou Port (Fujian province), and consequently by the same arti-sans when they settled in Manila. Moreover, in the South-EasternPhilippines, there existed elephants, precisely on Joló Island, thoughthese were smaller in comparison to the same species in the rest ofSouth-East Asia.

This work lead to the analytical study of more Hispano-Philippineimages, from the XVIIIth and XIXth centuries, in order to establishwhether there existed a continuity in the use of this material, or onthe contrary, if there was a progressive change in the raw material

Fig. 6. Spectra obtained by EDX for sample mvi-1. The presence of Ca and P, together withthe laminar morphology observed in the images, correspond to a hydroxyapatite.

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used when the new route thought the Cape of Good Hope, which con-nected Cádiz directly with Manila.

4.2. Conservation and polychrome

The images obtained by SEM for the 4 studied samples provide valu-able information about this image:

4.2.1. Sample 1 (mvi-1).This sample was collected from the inner part of the image (den-

tine). The structure of the ivory appears compact, and has a laminar

Fig. 7. a), d) and g): SEM images of different points in the samples show the presence of differentron images shows color/shine contrast due to different chemical compositions. c), f) and i): EDX(Cu). An aluminosilicate, the main component of a bole, is present. Finally, there are small amofirst preparation layer of gesso fine.

structure composed of platy layers parallel to each other, forming astep-like pattern (Fig. 5a). At high magnification, dentine tubules,which are typical in tooth morphology, are observed (Fig. 5b), as wellas small platy layers. The presence of Ca and P obtained by the EDXanal-ysis (Fig. 6) of these platy structures corresponds to carbonate-hydroxyapatite crystals.

Moreover, there is evidence of the alteration of the sample that isconsistent with its known history, as observed in Fig. 6. The presenceof biological microorganisms with an elongated shape (Fig. 6a and b),as well as the presence of spores (Fig. 7b) confirms the presence offungi typically found in dark and humid environments. This is consis-tent with the known burial period of this image during the SpanishCivil War. EDX analysis only supports the organic nature of thesemicroorganisms.

4.2.2. Sample 2 (mvi-2)This samplewas collected from the base/stand of the image (Fig. 3c).

It is of a brown colour, and contains glue residue. The results of EDXanalysis basically show an organic compound corresponding to glue,and small particles composed mainly of iron, along with smalleramounts of silicon, aluminium, sulphur, and chlorine.

4.2.3. Samples 3 (mvi-3) and 4 (mvi-4).The study of samples mvi-3 and mvi-4 provided information about

gilding. Fig. 7b illustrates a representative zone of mvi-3, wheresuperimposed layers are observed. The Backscattered Electron Image(Fig. 7b) confirms two zones with different chemical compositions.The EDX analysis of the brightest part (Fig. 7c) confirms the presence

t layers of materials used in the decoration of the image. b), e) and h): Backscattered elec-analysis identifies the use of an alloy of gold (Au), alongwith some silver (Ag) and copper

unts of calcium (Ca) and sulphur (S), corresponding to gypsum (CaSO4), and suggesting a

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of an alloy sheetwith a high gold content (Au,with a small amount of Agand Cu).

Sample mvi-4 supplied information about the binder used as a basein the gilding process. Fig. 7d shows again a very thin, shiny layer of goldover other material. The Backscattered Image (Fig. 7e) and EDX analysisverify the presence of scattered particles rich in calcium and sulphur(Fig. 7i). This composition could correspond to gypsum (CaSO4·H2O),used as a base layer and known as gesso. Its function is to close thepores, and to create a hard, smooth surface. It is mixed with animalglue to allow rapid bonding with the surface.

The use of a small layer of gesso (gesso fine) covering the ivory im-ages has been reported previously (e.g. Kowalski 204,Mendoza-Cuevas,2008, Sandu et al., 2010).

Fig. 7g and h also show a thin leaf of gold, approximately 2 μmthick, over a material composed of flake particles typical of clay min-erals. EDX analysis also confirms the presence of primary silicon, withlesser amounts of aluminium, magnesium, calcium, iron, and oxygen.The composition is of aluminium silicate, which is the main compoundof bole. The function of the bole is chromatic, as it gives anochre/reddishtonality, aswell as a base for gilding. The use of ochre pigments has beendocumented in gothic ivories (Casio and Levy, 1998, Gaborit-Chopin,1997; Guineau, 1999), and following the composition results of thisstudy, could be related with ochre de rue.

Fig. 8. a) A cross-section image shows the different layers over the ivory. A clear, ocre-coloured layer and a very thin, shiny layer of gold are observedwith an opticalmicroscope.b) SEM images of the cross section and an EDX analysis show the presence of 3 layers. Thefirst on is composed of scattered particles of gypsum and organic material (gesso fine).Layer 2 confirms the presence of aluminosilicate/clay as a component of a bole. Finally,layer 3 corresponds to a thin layer (around 2μm)of an alloy of goldwith silver and copper.

Finally, images of cross-section samples with optical and scanningelectron microscopes support the results obtained so far. Fig. 8a clearlyshows an ochre layer, consistent with bole. Remnants of gold leaf arepresent, and can be clearly observed in Fig. 8b. Also, a very thin layerof gesso was assumed, and was verified by EDX analysis.

The results obtained in this study let us propose that the gildingtechnique used to decorate the Immaculate Conception image waswater gilding (“guazzo”) over an oil/mordant gilding. Water gildinguses a layer of gesso and a layer of bole to make the gold leaf adhere,and it was traditionally used for wood surfaces, but has also been docu-mented for some medieval ivory sculptures. The study of gothic ivorystatuettes at the Louvre and other international collections reveals theuse of a bole of oil, resin, and ochre pigments as a common technique(Casio and Levy, 1998, Gaborit-Chopin, 1997; Guineau, 1999), whichcould have be inherited from the Hispano-Philippine images.

5. Conclusions

The following conclusions may be drawn from this research:The FTIR study confirms the origin of the primary material used to

carve the Immaculate Conception image as Asian elephant tusk. Thissupport the idea that Asian ivory from India and South-East Asia wascommonly carved by the artisans in the area of Zhanzhou Port (Fujianprovince), and consequently by the same artisans when they settledin Manila.

The SEM study verifies the authenticity of the ivory and shows evi-dence that the alteration of the sample is consistent with its knownhistory.

Moreover, it lets us propose that the gilding technique used waswater gilding (“guazzo”) over oil/mordant gilding. Water gilding usesa layer of gesso and a layer of bole to make the gold leaf adhere. It wastraditionally used for wood surfaces, but has also been documentedfor some medieval ivory sculptures.

This study has led to new research lines: On one hand, the ongoingstudy of Hispano-Philippine images from different centuries (from theXVIIIth to the XIXth) will let us establish whether there existed a conti-nuity in the use of this material, or on the contrary, if there was a pro-gressive change in the raw material used when the new route thoughtthe Cape of Good Hope, which connected Cádiz directly with Manila.On the other hand, a deeper research of the gold used in decorationwill confirm whether Hispano-Philippine ivories were only producedin Manila, or otherwise, whether there was a real contribution by Chi-nese artisans who settled in Mexico.

“This research was supported by the project “Estudio de lamicroestructura y composición de un marfil hispanofilipino del sigloXVII,” financed by Plan Propio de Investigación. Vicerrectorado de PolíticaCientífica e Investigación de la Universidad de Granada (UGR) 2013”.

Acknowledgements

The authors thank Dr. Isabel Guerra Tschuschke for her assistancewith and interpretation of SEM images and analysis, and Miguel MartínQuesada for his preparation of the cross section sample. We would alsolike to thank José Antonio Lozano from IACT and Antonio Pérez, fromTaxidermia Mompiel, for the Loxodonta africana tusk sample.

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