New insight on the underdrawing of 16th Flemish-Portuguese easel paintings by combined surface analysis and microanalytical techniques

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ContentslistsavailableatScienceDirect

Micron

jo u r n al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / m i c r o n

New

insight

on

the

underdrawing

of

16th

Flemish-Portuguese

easel

paintings

by

combined

surface

analysis

and

microanalytical

techniques

S. Valadas

a

_,

_R.

_Freire

a,b

_,

_A.

_Cardoso

a

_,

_J.

_Mirão

a

_,

_P.

_Vandenabeele

c

_,

_J.O.

_Caetano

d

_,

A. Candeias

a,e,∗

a_Évora_University,_HERCULES_Laboratory,_School_of_Sciences_and_Technology,_Largo_Marquês_de_Marialva_8,_7000-809_Évora,_Portugal b_Évora_University,_{CHAIA—Centre}_for_Art_History_and_Artistic_Research,_Largo_Marquês_de_Marialva_8,_7000-809_Évora,_Portugal c_Ghent_University,_Archaeology_Department,_{Sint-Pietersnieuwstraat}_35,_B-9000_Ghent,_Belgium

d_National_Ancient_Art_Museum,_General_Directorate_of_Cultural_Heritage,_Rua_das_Janelas_Verdes,_1300-001_Lisbon,_Portugal e_Jose_de_Figueiredo_Laboratory,_General_Directorate_of_Cultural_Heritage,_Rua_das_janelas_verdes_37,_1300-001_Lisbon,_Portugal

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received1December2015

Receivedinrevisedform13March2016 Accepted14March2016

Availableonline17March2016

Keywords: Underdrawing Easelpaintings

16thcenturyportuguese-Flemish workshop

Infraredsurfaceexams SEM-EDX

␮-Ramanspectroscopy

a

b

s

t

r

a

c

t

Thispaperfocussesonthestudyoftheunderdrawingsof16thcenturyeaselpaintingsattributedtothe workshopofthePortuguese-FlemishMasterFreiCarlos.Thisinvestigationencompassesmultidisciplinary researchthatrelatestheresultsofsurfaceexams(infraredreﬂectography,standardlightphotography andinfraredphotography)withanalyticalinvestigations.

ThesurfaceanalysisofFreiCarlos’underdrawingsbyinfraredreflectographyhasshownheterogeneous work,revealingtwodifferentsituations:(1)anabundantandexpressiveunderdrawing,revealinga Flem-ishinfluenceand(2)asimpleandoutlinedunderdrawing.Thispreliminaryresearchraisedanimportant questionrelatedtothisPortuguese-Flemishworkshopandtotheanalyticalapproach:Isthe underdraw-ing’sheterogeneity,asobservedinthereflectograms,relatedtodifferentartistsoristhisratheraneffect thatisproducedduetotheuseofdifferentmaterialsintheunderdrawing’sexecution?Consequently, ifdifferentmaterialswereused,howcanwehaveaccesstothehiddenunderdrawings?Inorderto understandthereasonsforthisdissemblance,chemicalanalysisofmicro-samplescollectedin under-drawingareasandrepresentingbothsituationswerecarriedoutbyopticalmicroscopy,microFourier transforminfraredspectroscopy(␮-FTIR),scanningelectronmicroscopycoupledwithenergydispersive X-rayspectrometry(SEM-EDX)andmicro-Ramanspectroscopy(␮-Raman).Takingintoaccountthe dif-ferentpossibilitiesandpracticalandtheoreticallimitationsofsurfaceandpunctualexaminationsinthe studyofeaselpaintingunderdrawings,themethodologyofresearchwasadjusted,sometimesresulting inare-analysisofexperimentalresults.Thisresearchshowstheimportanceofcombining multispec-tralsurfaceexamsandchemicalanalysisintheunderstandingoftheartisticcreativeprocessesof16th centuryeaselpaintings.

1. Introduction

Underdrawingsarethepreliminarydrawingsonthepanels(or

canvas)andmuchofinterestinthisstudyliesinwhattheyreveal

about thecreative processes of the artist, providing important

informationaboutworkshopsanddevelopmentsinacertaintime

period(Bomfordetal.,2002;Kammereretal.,2007).

∗ Correspondingauthorat:ÉvoraUniversity,HERCULESLaboratory,Schoolof SciencesandTechnology,LargoMarquêsde8,Évora,Marialva,7000-809,Portugal.

E-mailaddress:[email protected](A.Candeias).

Infrared reﬂectographyhasbeenthetechnique most widely

usedforrevealingandstudyingunderdrawings.Since its

devel-opmentinthelateof60softhetwentiethcenturybytheDutch

physicist Van Asperende Boer(Boer, 1968,1970), theinfrared

reﬂectographytechnique hasbeenanimportant tool for thein

situanalysisanddiagnosisofworks ofart(Faries,2005),

allow-ing toreveal theunderdrawings under layers of paintthrough

selectivereﬂection/absorptionofinfraredradiationbythevarious

constituent materials.Drawing,strokes,signatures, inscriptions,

mechanicaltransferprocesses,pentimentiandchangesof

compo-sitionhiddenbeneathlayersofpaintcanbeobservedandrevealed,

allowing a deeper knowledge of the technique of an artist or

http://dx.doi.org/10.1016/j.micron.2016.03.004

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workshop.Anotherimportantaspectconcernstothestyleofthe

underdrawing,whethertheunderdrawingisasimplesketch,

free-handorrathermethodicalandorderly.Finally,anotherimportant

issueconcernstotheidentiﬁcationofthematerialsanddrawing

toolsusedin thecreation oftheunderdrawing(Bomfordetal.,

2002;FischerandKakoulli,2006;Kammereretal.,2007;Candeias etal.,2011).

Thenatureofmaterialsusedintheunderdrawingsexecution

usually involves analytical research, which includes

micro-sampling,microscopy observationsand micro-analysis.It is not

alwayspossibletocollectmicro-samplesand,evenwhenitis

pos-sible,verysmallamountsofsampleareobtainedandevenmuch

smalleramountsofunderdrawingmaterialareavailablefor

anal-ysis.Additionally,onehastotakeintoaccountthefactthatthe

underdrawingislocatedbetweenpaintlayersandthereforeone

hastoconsiderthenatureofmaterialspresentinadjacentlayers,

whichcouldnotonlyhamperitsvisibilitythroughinfraredimaging

toolsbutalsotheycouldcompromisesomehowtheanalyticaldata.

Ontheotherhand,anumberofmaterialsusedtocreate

underdraw-ingdesignsarebasedonsomeformofcarbonandsometimes,even

withadeeperchemicalanalysis,itisnotpossibletodistinguish

betweenthem(Bomfordetal.,2002).Atthis level,bothsurface

analysisbyinfraredlightandmicro-analyticalresearchshouldbe

complementedbyeachother,givinginformationontheresponseof

thedrawingmaterialsatinfraredlight(e.g.visibleornotvisible,dry

orﬂuid)andrelatingthistotheiropticalpropertiesandchemical

composition(Bomfordetal.,2002).Moredifﬁcultisthe

identiﬁ-cationofcarbonandmetal-basedinks,asithaspoorresponsein

infraredreﬂectography.Thishindersthemicro-samplingprocess

andalso,duetothecomplexityofcompoundsthatcouldbepresent

(e.g.irongallinksandrespectivegallatonatecompounds),its

chem-icalcharacterization.Theseseemtobethemajorreasonswhyvery

few,andextraordinary,analyticalstudiesofthesematerialshave

beenpublished(DunkertonandRoy,1986;Springetal.,2009).

Thecharacterizationoftheunderdrawinginallthoseaspects

couldcontribute,atthelimit,toanswersomequestionsrelatedto

theattributionandauthenticationofworksofart.

Thispaperpresentsanextensiveresearchbasedonthetechnical

andmaterialcharacterizationoftheunderdrawingofsixteen

cen-turyPortuguese-FlemisheaselpaintingsattributedtoFreiCarlos’

Workshop.

Frei Carlos, one of the most important “Portuguese-Flemish

Painters”,workingintheregionof Évora(activebetween1517

and1539–40),leftalargenumberofworksthatcomemainlyfrom

theEspinheiro’sConventwherehemadetheProfessionofFaith

(in1517).“Portuguese-FlemishPainting”isacommonexpression

usedintheHistoryofPortugueseartoftheﬁrstthirdofthe

six-teenthcentury and inits mostbasicmeaningit designatesthe

workofFlemishMasterswhosettledinPortugalduringthereign

ofKingManuel(1495–1521)contributingdecisivelytothe

pro-cessofrenewalofPortuguesepaintingatthetime(Santos,1971).

However,thedesignationsurpassesthissimpleandobjective

per-spectivewhenittendstotransformitintoaconceptwithhigher

operatinginterpretativeambitions,asforexample,whenitis

sug-gestedthatsuchFlemishmasters“adaptedtheirworkprocessesto

theaestheticconceptsandspiritualclimateprevailinginthe

work-shopsofthePortuguesemasters,butwithoutlosingthequalities

andtechnicalskillsacquiredintheFlemishworkshopswherethey

didthelearning”(Santos,1971).Or,goingfurther,whenone

con-sidersthatthe“fusionofthecharacteristicsofthetwoschools”,

PortugueseandFlemish,originated“astyle,whichiscommonly

calledthePortuguese-Flemish”(Santos,1971).

Itisofutmostimportancetodoresearchthatwilldeliver

fun-damentalnewdataaboutthetechniquesofartisticproductionand

thematerialityoftheworks.Ultimately,itwillallowusto

iden-tifypossiblesimilaritieswithworksofFlemishpaintersoftheir

time,openingupchancestodeterminethecentres(Bruges,Ghent,

Antwerp,orothers)wheretheymighthavestartedtheircareers

beforearrivingtoPortugalandthatthedocumentalsourcesomit.

TheﬁrststeptounderstandtheFreiCarlos’workshopwasthe

pioneeringwork of Couto(Couto,1943)which based his

attri-butions by combiningvisual examinationswithsurface exams,

concludingthatthetechnicalandstylisticdifferencesdidnotshow

changesinthewayofpaintingofasingleMasterbutinsteadwere

theresultofcollaborationofseveralofﬁcinalpainters.Acritical

review oftheseargumentswaslater donebytheArtHistorian

SeabraCarvalho(Carvalho,1988–1993,1998,2006,2011)which

concludedthattwotypesofpictorialpreparatorydrawingseemed

toappear in theworkshopcreation, perhapsindicating a more

complexinternalstructure.Morerecently,newdataobtainedby

infraredreﬂectographyconﬁrmtheheterogeneouscreative

pro-cessofthisworkshopandtheneedofadeeperresourcebasedon

thechemicalcompositionofthematerials(Candeiasetal.,2011;

Carvalho,2013).

A deepinvestigation of this Master workshop and practices

isbeing developedthrough multi-disciplinaryteamscombining

historical research ondocumental sources with surface

exami-nationandmaterialcharacterizationusingstate-of-artanalytical

techniques.Theresultsobtainedsofarhighlightseveral

similari-tiesbetweenFreiCarlos’workshopandFlemishschools,regarding

materialsandsomeparticularitiesofthetechniqueofartistic

pro-duction(Valadasetal.,2013,2014).

Thisinvestigationbringsnewperspectiveoftheworkattributed

tothisworkshop,thoughtthetechnicalandmaterial

characteriza-tionoftheﬁrstsketchofanartistwhenhestartshiswork,the

underdrawing.

2. Materialsandmethods

2.1. Surfaceanalysis

The study of 16th Century Portuguese-Flemish paintings

attributed to the Master Frei Carlos’ workshop started with

the visual examination of the paintings and surface exams,

namely standard light photography, U.V. ﬂuorescence

photog-raphy, infrared reﬂectography, infrared photography and X-ray

radiography.

Standardlightphotographywasperformedwithahigh

resolu-tiondigitalcameraNikonD3100equippedwithaCMOSsensor(DX

format,14.2effectivemegapixel)andlensesAF-SDXzoom-Nikkor

18–55mmf/3.5–5.6GEDII.Twolampswithtungstenlightbulbs

and3200Kcolourtemperaturewereusedtouniformlyilluminate

eachofthepaintings.ThedetailswererealizedwithaNikonAF-S

DXMicroNikkor40mmf/2.8lens.

Thereﬂectograms wereobtainedby using a highresolution

infrared reﬂectography camera (Osíris) with an InGaAs

detec-torallowing a wavelengthresponse from 900to1700nm, and

equippedwitha16×16cm2 _tile_system_which_allows_an_image

sizeof4096×4096pixels.Thecameracomeswithalongpassﬁlter

SchottRG850,allowingtotransmitinfraredwavelengthandblock

theundesiredshorterwavelengthuntil850nm.Thereﬂectograms

wereperformedfor45×45cm2_painting_area.

Infrared photography was performed with a digital camera

Nikon D3100 that wasmade sensitive toinfrared radiation by

removingthelow-passﬁlterandoperatingwithlensesAF-SDX

MicroNikkor40mmf/2.8G. Theinfraredradiationstartsonthe

visibleradiationlimitaboveredtillhertzianwaves,from730to

105_nm_however,_only_a _part_can_be_registered_by_photography:

thenearinfraredthatgoestill1100nm.Thissystemwasalso

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Table1

AnalysisoftheunderdrawingsinthepaintingsattributedtoFreiCarlosworkshopandhisfollower.

Titleof

painting/inventory number

Date Provenance Underdrawingidentiﬁcation

Bestresponse

areaexams

Technique Material

Anunciation MNAA677pint Dated1523a _St._Maria_do_Espinheiro

Monastery

IRR+IRP FH:ﬂuidmedia C+IG

IRR T:pouncing(brocade) C

RX Metal-point –

Mysticmarriageof SaintCatherine

MNAA54pint c.1517–1538b _St._Maria_do_Espinheiro

Monastery(?)

IRR FH:ﬂuidmedia C

ThreeSaints MNAA174pint c.1517–1538b _St._Maria_do_Espinheiro

Monastery(?)

St.Francisreceiving thestigmata

MNAA276pint c.1520–1530c _Lóios_Monastery _IRR _FH:_ﬂuid_media;

Drydrawingmedia

C

St.Anthonyandthe Child

MNAA64pint c.1520–1530c _Lóios_Monastery _IRR _FH:_ﬂuid_media _C

RX Metal-point –

St.SebastianeSt. Vicent (FollowerofFrei Carlosd₎

MNAA100pint c.1530–1540?d _St._Vicente_de_Fora

Monastery

IRR FH:ﬂuidmedia;T: pouncing(brocade)

C

VirginwiththeChild andanangel (FollowerofFrei Carlosd₎

MNAA58pint c.1530–1540?d _St._Vicente_de_Fora

Monastery

C

RX Metal-point –

AppearanceofChrist totheVirgin

MNAA2pint Dated1529 St.MariadoEspinheiro Monastery

<IRR FH:ﬂuidmedia C+IG

RX Metal-point –

Verónica MNAA51pint 1sthalfof16th century

St.MariadoEspinheiro Monastery

C

ProfessionofSt. Paula

MNAA85pint 1sthalfof16th century

St.MariadoEspinheiro Monastery(?)

RX Metal-point –

Assumptionofthe Virgin

MNAA82pint 1sthalfof16th century

IRP FH:ﬂuidmedia C+IG

AscensionofChrist MNAA83pint 1sthalfof16th century

IRR T:pouncing(brocade) C EcceHomo MNAA

2184pint

c.1530a _Unknown _IRR _FH:_ﬂuid_media _C

St.Brás ME1523 c.1520–1530d _Santa_Maria_do

EspinheiroMonastery (?)

<IRR FH:ﬂuidmedia C+IG

IRR T:pouncing(brocade) C St.Cristóvão ME1524 1sthalfof16th

century

St.MariadoEspinheiro Monastery(?)

<IRR FH –

Nativity ME1525 c.1520–1525a _St._Maria_do_Espinheiro

Monastery

<IRR FH:ﬂuidmedia; C+IG

IRR FH:Drydrawingmedia C Lamentation MNAA74pint c.1530a _St._Maria_do_Espinheiro

Monastery

C

GoodShepherd MNAA1pint c.1520–1525a _St._Maria_do_Espinheiro

Monastery

IRR FH:Drydrawing media;

T:pouncing(brocade) C

RX Metal-point –

Resurrection MNAA73pint 1sthalfof16th century

IRR+IRP FH:ﬂuidmedia C+IG

Virginwithachild andtwoangels (front)andChrist Blessing(back) MNAA 1179pint 1sthalfof16th century St.MariadeBelém Monastery

CalvaryTriptych MNAA 2173pint

c.1520–1530d _Quinta_da_Palmeira,

Seixal

RX Metal-point –

IRR—betterbyinfraredreﬂectography;IRR+IRP—combinationofIRRwithIRP;IRP—betterresponsewithinfraredphotography;<IRR—lowresponsebyIRR;RX—detectedby X-rayradiography.FH—freehand;T—Transferprocess.C—carbon;IG—iron-gallink;MP—metal-point.

a_Caetano,_J.O.,_Mestres_{Luso-Flamengos}_em_Évora₋_A_pintura_e_o_desenho,_in_Primitivos_Portugueses_{1450–1550—O}_Seculo_de_Nuno_Goncalves,_MNAA_and_IMC_(Eds.),

2011,pp.276–293.

b_Archival_inventory_database_matriz_net:_{www.matriznet.imc-ip.pt}_.

c _Carvalho,_J.A.S.,_Dois_Mestres_{Luso-Flamengos:}_Mestre_da_Lourinhã_e_Frei_Carlos,_in_Primitivos_Portugueses_{1450–1550—O}_Século_de_Nuno_Gonc¸_alves,_MNAA_and_IMC

(Eds.),2011,pp.156–173.

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Fig.1.Surfaceexams:(a)and(b)detailofEcceHomobystandardlightphotographyandinfraredreﬂectography,respectively,showinganabundantandexpressive under-drawing(representativeofsituation(a));(c)and(d)detailofVirginwiththeChildandtwoangelsthroughstandardlightphotographyandinfraredreﬂectography,respectively (thearrowsindicatetheregionswhereunderdrawingiswellvisibleatnakedeye).Photographiccredits:(a)and(b)SóniaCosta,(c)RitaFreireandSaraValadas,(d)Luís Piorro.

thatblock50%oftheinfraredlightandallowsinfraredlighttopass

untilthelimitofdetectionofthecamera.

2.2. Micro-analyticaltechniques

Thisstudyencompassestheanalyticalandtechnicalresearch

oftwentyonepaintingsattributedtoFreiCarlos’workshop(see

Table1),focusingonthestudyoftheunderdrawings.The

selec-tionofrepresentativeunderdrawingareasformicrosamplingwas

supportedbyimagingtechniques.Microfragmentswerecollected

andmountedinepoxyresininordertoexposethepaintlayersfor

furtheranalysis.

Opticalmicroscopy observations(×100and ×200

magniﬁca-tions)and thecorrespondingphotographicdocumentationwere

obtainedbyadark-ﬁeldmicroscope(LeicaDM2500,equippedwith

aLeicaDFC290HDcamera).

Scanningelectronmicroscopycoupledwithenergydispersive

X-rayspectroscopy(SEM-EDX)werecarriedoutusingaHitachi

S-3700NscanningelectronmicroscopecoupledwithaBrukerXFlash

5010SDDdetector.Thesamples(cross-sections)were analysed

throughlow vacuum,at40Pa and thevoltageusedwas 20kV.

Thisanalyticalsetupallowedtheidentiﬁcationofparticleswith

dif-ferentcompositionbycombiningelectronbackscatteringimaging

withEDSanalysis,andalsoprovidedgoodqualityX-ray

composi-tionalmaps.

TheMolecularanalysisofunderdrawingmaterialsstartedwith

aNexus®670␮-FTIRcoupledtoaNicoletContinuummicroscope

byThermoNicolet,intherange600–4000cm−1,withanIRsource,

KBrbeamsplitter anda DMCTdetectorforMIRmeasurements.

Individualsamplelayerswereobtainedbyphysicaldissectionand

thin-sectionswereobtainedbysqueezingeachsample between

twodiamondcells.Foreachsample256scanswererecordedwith

aresolutionof4cm−1.

Cross-sectionsofunderdrawingareaswereanalysedbyaHoriba

Xplora confocalmicro Raman spectrometer,which is equipped

withanOlympusBX41cameraandaCCDdetector.The

characteri-zationofunderdrawingmaterialswasperformedbyusingaHe-Ne

laseroperatingat785nm.Non-destructiveanalyseswereensured

bycombiningdensityﬁlters(maximum10%)anda100×objective,

resultinginapoweratthesampleofapproximately1mW.

3. Results

3.1. Surfaceanalysis

Several historical and technical questions (Caetano, 2011;

Carvalho,2011,2013)relatedtothecharacterizationofthe

under-drawingsinEspinheiro´ısworkshopcouldbesolvedbyextensive

researchbasedonthecombinationofstandardlightphotography

andinfraredreﬂectography.Throughtheanalysisofthepaintings

surfacesbynakedeye,onecanseethattheunderdrawingseems

tobeveryabundant.Thisisclearonseveralareassuchas

carna-tions,lightareasordamagedareas.However,thecombinedresults

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Fig.2.Opticalmicroscopyofcrosssectionscontainingunderdrawing,where(a)correspondtosituation(c)and(b)illustratessituation(d).

a)Inseveralpaintings,infraredreﬂectographyrevealedan

abun-dantandexpressiveunderdrawing,pointingtotheuseofawet

medium.Sometimesitisalsopossibletoseedropletsattheends

ofstrokes,whichseemstoconﬁrmthis;

b)Inothersituations, althoughonecan evenseebynakedeye

hatchedandcross-hatchedunderdrawingatthepaintings

sur-face, the reﬂectograms only revealed a thin and outlined

underdrawing.

X-rayradiographyandinfraredreﬂectographyhaveshown

pre-viouslytheexistenceofreservedareas,anabundantandexpressive

underdrawingpresentinseveralpaintingsandthelackofchanges

in composition that revealed how the work was meticulously

planned.Consideringthisworkshoppractice,itwasexpectedthat

similarworkwouldbepresentintheotherpaintingsattributed

tothesameworkshopwheretheunderdrawingisnotdetectable

byinfraredreﬂectography.Furthermore,previousstudies(Billinge

et al., 1997; Bomford et al., 2002; Finaldi and Garrido, 2006; Tamarit,2006;VerriandHiggitt,2010)developedonﬁfteenand

sixteencenturyFlemishand Italianeaselpaintingsindicatethat

whenartistsusenon-carbonaceous-basedinks,underdrawingis

notvisibleorispoorlyvisibleininfraredsurfaceexams.A

simi-larsituationcouldbethereasonfortheunconformityofthedata

found,pointingtoamaterialissuethatcanonlybesettledwith

supplementaryanalyticalinvestigations.

3.2. Microanalysis

Concerningtheunderdrawingdetectionbyinfrared

reﬂectogra-phy,twosituationstookplaceasmentionedbefore(situations(a)

and(b)).Theanalyticalstudyoftheseunderdrawingsreliedonthe

dataobtainedbysurfaceexaminationsandthepossibilityto

col-lectmicrosamplesinspeciﬁcareas.Thelatter,however,ishighly

dependentonthemuseumcontextinwhichthepaintingsareand

theirstateofconservation.

Due to the thinness of the underdrawing layers, analytical

research started with the preparation of the micro-samples in

cross-sectionsanddarkﬁeldmicroscopicalobservation.The

strati-graphicanalysisrevealedsomeopticallydistinguishableproperties

intheunderdrawingslayers(Fig.2):

c)In mostcases,theunderdrawinglayerappearsasan

irregu-lar/notcontinuouslinecontainingeitherisolatedblackparticles

ordistinguisheddepositsofablackmaterialappliedoverthe

preparationlayer;

d)Sometimes,itispossibletodistinguishacontinuousand

home-geousdarkbrown/blacklayerappliedoverthepreparationlayer,

pointingtotheuseofaﬂuidmaterial,corroboratingtheuseof

awettechnique.

Bycomparingallabovesituationswecansuggestthatwhen

theunderdrawingiswellvisiblethroughinfraredreﬂectography,

itseemstobemorelikelytocorrespondtosituation(c)andthe

blackisolatedoraglomeratedparticlesshouldcontainsome

car-bonaceousmaterial.Nevertheless,whenthesituation(d)occurs,

itseemstocorrespondtothosecaseswheretheunderdrawingis

poorly/notvisiblebyinfraredreﬂectography(situation(b)),

point-ingtotheuseofa differentmaterialappliedinawetmedium.

Despitethementionedcorrelations,sometimesitishardto

distin-guishbetweenthem,sincetheyarenotexclusivefromeachother.

Ontheotherhand,thecharacterizationoftheunderdrawinglayers

throughopticalpropertiesletsusexcludetheuseofcommon

mate-rialssuchassomecolouredchalks,ascitedinliterature(Bomford

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Fig.3. Analysisofanunderdrawingregion(microsamplecollectedfromtheVeronica):microsamplingárea(a)andrespectivecross-section(b);andSEM-EDXanalysis showingBSEimagewithindicationofpunctualEDXanalysis(c)andtherespectiveEDXspectrumoftheunderdrawingarea(d).

In conclusion, although optical microscopy gave some clues

aboutthetechniqueandthenatureofthematerialsusedinthe

underdrawingsexecutionitremainstoanswerwhichmaterialis

responsiblefortheinvisibilityoftheunderdrawinginsituation(b).

Inthisparticularcase,stratigraphicanalysisalsoadvanceda

possi-blematchofthismaterialdemonstratingthatitseemstobeapplied

inawetmediumand,takingintoaccount,thereisahigh

proba-bililityoftheuseofanirongallink(Campbell,1998;Bomfordetal.,

2002).

Furtheranalyticalresearchwascarriedoutinordertoascertain

thenatureofthismaterial.Cross-sectionsrepresentativeforboth

situationsandcontainingrelativelyhighamountsof

underdraw-ingmaterial,wereselectedandsubmittedtoSEM-EDXanalysis,

givingsomeindicationsaboutthenatureofthematerialsusedin

theunderdrawingsexecution.

Elementalanalysesrevealedtheuseofacarbonbasedmaterial

(probablycarbonblack)inpaintingswheretheunderdrawingis

wellvisiblebyinfraredreﬂectography(situation(a)seeFig.3),as

expected.

Ontheotherhand,SEM-EDXanalysisrevealedanenrichmentin

iron(Fe)inthepaintingswheretheunderdrawingisnotvisibleor

isbarelyvisiblebyinfraredreﬂectography,relatedtosituations(b),

(Fig.4).AccordingtopreviousstudiesbasedonSEM-EDXanalysisof

easelpaintings´ıunderdrawings(DunkertonandRoy,1986;Spring

etal.,2009)wecanproposethehypothesisoftheuseofirongallink.

Besidestheironcontent,SEM-EDXanalysisalsorevealedthe

pres-enceofmagnesiumandaluminumasminorelements(Fig.4g))and

sometimesitalsorevealedsometracesofcopperwhich,according

toseveralstudiesonhistoricalmanuscripts,couldbeassociatedto

ironsulphatecontaminationsintheinkformulation(Hahnetal.,

2004).Several studies(Camera, 2004; Hahn et al., 2004; Kolar

etal.,2006)onthecharacterizationofirongallinksinhistorical

manuscriptsthroughelementalanalysis(SEM-EDXand/orPIXE)

alsoreferthepossiblepresenceof otherelementssuchaszinc,

manganese,sulfur,calcium,potassium,sodium,cobalt,nickeland

silica.Althoughpunctualanalysisalsopointstothepresenceof

calciumintheunderdrawingarea(Fig.4c)andg)),onehastotake

thenatureofnearbylayersintoconsiderationwherethiselement

couldbepresent,e.g.thepreparationlayerconsistsofacalcium

basedmaterial(e.g.calciteorgypsum)(Valadasetal.,2013),raising

somedubietyaboutitspresenceasacontaminantoftheink.

Compositionalelementalmappings alsorevealedahigh

con-tentofcarbonandoxygenintheunderdrawinglayers,suggesting

anadditionofanorganicmaterial,probablycomingfromthe

bind-ingmediausedintheinkformulation.Moreover,thisanalytical

techniquealsorevealedinsomecasestheadditionofnoticeable

isolatedcarbonparticlestotheironbasedmaterial,appearing

par-tiallymixedandpointingtoapossibleexistenceofathirdmaterial

usedbythisworkshopintheunderdrawingsexecution.

Additionally,despitethepresenceofironandcopperin

metal-gallinks(Acetoetal.,2008),theseelementscanalsooccurasmetal

impuritiesincarbon-basedinks.Althoughthemetalconcentration

isoftenagoodindicatorofthemetalsource,fulldiscrimination

isonlypossibleifcomplementedbymolecularinformationabout

theinkorganic/organometalliccomponents(tanninsand

metal-complexes).Theinfraredimagesof thepaintings mightsuggest

certainmolecularspecies,butarenotconclusive.Theanswerto

theserisinghypothesescanthereforebeprovidedbytechniquesfor

structuralanalysisinthestudyofnon-carbon-based

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Fig.4. Analysisofamicrosamplecontaingunderdrawing,collectedfromtheVirginwiththeChildandtwoangels(#VF7):(a)microsamplingarea;(b)cross-sectionofrespective region;andSEM-EDXanalysisrevealinginimage(c)thecombinedelementalmapping,(d)and(e)compositionalelementalmaps,(f)BSEimageindicatingthelocalofEDX analysisandin(g)therespectiveEDXspectrumoftheunderdrawingarea.

FTIRexperimentswereperformedinordertoallowthe

assign-ment of characteristic absorption bands of functional groups

associatedtounderdrawingareas.

␮-FTIRanalysiswasperformedinfewpaintingsattributedto

FreiCarlos’workshopwherepreparationsaremainlycomposedby

calcite,seekingtoeliminateasmuchaspossiblethe

contamina-tionsofsulfategroupspresentinthenearbygypsumpreparations,

foundinmostpaintings(Valadasetal.,2013).Theindividuallayers

ofunderdrawingwereobtainedthroughdissectionofthesamples

withascalpelandtheresultingthinsectionswerethenanalysed.

Fig.5showsthewavelengthassignmentsofunderdrawinglayers,

evidencingthepresenceofOHvibrationsinwatermoleculesand

thecontributionsofproteinandoilmediums.Tracesofcalcium

carbonateshouldalsobeconsideredand,although itspresence

hereisnot exclusivefor underdrawinglayers,this mineraland

relatedoxaliccompoundshavefrequentlybeenfoundinirongall

inkcomposition(FerrerandSistach,2005).Recordedspectraalso

displaycharacteristicabsorptionbands,duetothe3

antisymmet-ricstretchingvibrationsinsulfatefunctionalgroupsintherange

1300–1000cm−1 and typicalbendingassignment,which occurs

around680–600cm−1(Derricketal.,2000;Rouchonetal.,2012).

Thebandsat1109cm−1 and672cm−1 aretypicalforanhydrite

(CaSO4),andarerelatedtothe␯3antisymmetricstretchvibration

and␯4antisymmetricbendingvibration,respectively.Anhydrite

usuallyexhibitsoneweakbandat1015cm−1duetothe␯1

sym-metricstretchvibrationmodesofSO4tetrahedras,buthereitseems

tobeabsent(Liuetal.,2009;Meloetal.,2014).

ApreviousstudypublishedbyEspadaleretal.(Espadaleretal.,

1995)hasshownthepresenceofprecipitatedCaSO4betweenpaper

ﬁbers where iron gall ink had beenapplied and somehow our

resultspointtoasimilaroccurrence.Infact,severaloftheabove

mentionedstudiesreferthepresenceofcalciumasanink

contami-nant.Takingtheacidicenvironmentinwhichirongallinkisformed

andtheink’smetal-sulfateadditivesintoaccount (e.g.blue

vit-riol,CuSO4·5H2O,(Cennini,1954;Hahn,etal.,2004;Chiavarietal.,

2007)itisnotsurprisingthatsomeanhydritecouldbepresent.

Amoredifﬁcultassignmentconcernstotheoccurrenceoftwo

bandsat1077cm−1 and1042cm−1,stillintheregionofsulfate

groups,pointingtoadifferentsulfatebasedcompoundthatcould

bepossiblyrelatedtothepresenceofanironsulfatematerialused

inirongallink(Senvaitiene,2006;Bicchierietal.,2008a,b).

How-ever,whencomparingthefullrangeofassignmentswiththetypical

wavelengthsofiron gallinkcomplexes,gallatonatecompounds,

gallicacid,pyrogallolorevengumarabic,itdoesnotseemtoreveal

clearmatches(Mohammed-ZieglerandBilles,2002;Ursescuetal.,

2009).Thereasonsforthisabsencecanberelatedtothesmall

quan-tityofsampleavailableforanalysisandalsotothecontributionof

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Fig.5. RecordedFTIRspectrumofanunderdrawinglayercollectedfromamicrosampleoftheAnnounciation(#AN5).

couldbepresentintheunderdrawingareasandinadjacentlayers,

whichmaymaskthetypicalspectralregionsofthesecompounds.

␮-FTIRanalysishighlightedtheoccurrenceoffew functional

groupsfrequentlyfoundinirongallinksandrelatedcompounds

althoughthepresenceofthisunderdrawingmaterialcouldbeno

morethanamerelyhypothesis.

Complementary,␮-Ramananalysiswasperformedinseveral

underdrawingareasandthespectraobtainedinourworkwere

comparedwithspectraobtainedfrompreviousstudiesdeveloped

inancientmanuscriptsandpapers,comercialirongallinksandalso

withsomeexperimentalreprodutionsaccordingtoancientrecipes

(BrownandClark,2004;VandenabeeleandMoens,2004;Leeetal., 2006,2008;Chiavarietal.,2007;Acetoetal.,2008;Creaghetal., 2009).

Finally,atypicalspectrumof irongallinkwasobtainedand

isshowninFig.6,revealingthefourlargestbandsusedas

posi-tiveidentiﬁcationofthiscompound(Goltz,2012).Theseoccurred

at1468,1337,580and528cm−1(combinedbroadband).While

thebandat1468cm−1 ischaracteristicoftheiron-gallink

com-plex,thebandthatappearsat580cm−1 hasbeenassociatedto

aniron-organicsubstratecomplex/metallicsaltandseemstobe

independentoftheinkcomposition(Bicchierietal.,2008a,b).

Addi-tionally,somerecordedspectraalsopresentasharpbandaround

1012cm−1,probablyrelatedtoaresidualpresenceofsulfateanions

(Aceto et al., 2008).Sometimestraces of carbon black are also

detected,suggestingthatacarboninkunderdrawingmaterialwas

alsousedbythisworkshop.

Althoughtheobtained␮-Ramanspectrafrequentlypresented

poorresolutionandweakerbandsaboveahighﬂuorescence

base-line,thistechniqueallowedtheconﬁrmationoftheuseofirongall

inkbyFreiCarlos’workshopandthisiswithnodoubtthemain

resultofthiswork.Italsoleadstothejustiﬁcationfortheprevious

reporteddiscrepancy,observedbyinfraredreﬂectography.

Additionally,SEM-EDXanalysisalsorevealedanassociationof

iron-basedmaterialtocarbonparticles,risingthreemainsituations

relatedtothematerialsusedintheunderdrawings:

-Underdrawingmadewithacarbonbasedmaterial(probablyin

wetmedium).

-Underdrawingexecutedwithirongallink(wetmedium).

-Underdrawingmadewithamixtureofirongallinkandcarbon

(inaﬂuidprocess)orthereinforcementofirongallinkmaterial

overthecarbonunderdrawing(asexplainedbyCenninoCennini

inchapterCXXII,howthepaintersshoulddrawonpanelwith

charcoal,tobeginwith,andtoﬁxitwithink(Cennini,1954)).

Combiningtheseresultstosurfaceanalysis,weconﬁrmedthat

whentheunderdrawingisexecutedwithacarbonmaterial,itis

wellvisiblebyinfraredreﬂectographyasitwasexpected,butwhen

theironbasedmaterialispresenttheinfraredimageisnot

visi-bleorisbarelyvisible,probablydependingontheratioirongall

ink:carbon(seeTable1).

3.3. Surfaceanalysisreﬁnement

Takingintoconsideration:

-theresultsthatrevealtheuseofirongallinkinthisworkshop,

whichhasapoorresponseininfraredreﬂectographynotallowing

thecharacterizationofunderdrawingundertheseconditions;

-the recent studies based on DFT calculations using periodic

boundaryconditionsonirongall3Dcoordinationpolymerwhich

indicatethatthiscompoundhasamaximuminitsabsorption

spectrumataround700nm(Zaccaronetal.,2013a,b)and

previ-ousworkonirongallinksspectralabsorption(Senvaitien ˙eetal.,

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Fig.6.Ramanspectrumofirongallink(underdrawinglayercollectedfromamicrosampleoftheGoodShepherd,#BP10).

Fig.7. DetailoftheVirginwiththeChildandtwoangelsby:(a)standardlightphotography,(b)Infraredreﬂectography(850–1700nm)(c)Infraredphotography(1000–1100)nm and(d)Infraredphotography(780–1100nnm).Photographiccredits:(a)RitaFreireandSaraValadas;(b),(c)and(d)SaraValadasandSóniaCosta.

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-Previous studies based on multispectral and hyperspectral

imaging technologiesassessed ondrawing inks(Baker, 1985;

Kammereretal.,2007)andeaselpaintings(FischerandKakoulli, 2006);

we decided to reﬁne the surface analysis methodology to

perceive this type of underdrawing. Therefore, to capture the

underdrawingexecutedwiththismaterialthathadnotyetbeen

revealedbyinfraredreﬂectography,weusedseveralbandpass

ﬁl-terscoupledtoaninfraredphotographiccamera.

Theanalysisofthepaintingsurfacewithinfraredreﬂectography

andphotographytogetherwiththeanalyticalresearch,allowedus

toconclude:

-Inthe paintingswhere a carbonaceous materialwasused for

theunderdrawingexecution,infraredreﬂectographyrevealedan

abundantunderdrawing,betterthaninfraredphotography,asit

wasexpected.

-For thepaintingswhere iron gallinkwas mostlyused inthe

underdrawingsexecution,infraredphotographyrevealedbetter

results.(seeFig.7).Inthesecases,thetestsperformedbyinfrared

ﬁltersrevealedabettersignalforthe780nmﬁlter,probablydue

totheabsorptionoftheFebasedmaterialatlowerwavenumbers.

AlthoughIRRgavemoreinformationconcerningcarbon-based

materialsthat absorbathigher wavelengths,sometimesa new

analysisofpaintingsisneededbyusinglowerinfraredradiations,

thatcouldbeusefultorevealunderdrawingsmadewithsomeiron

gallink.

4. Conclusions

This multianalytical and interdisciplinary study enabled a

deeperinsightontheworkofFlemish-Portuguese16thcentury

painterFreiCarlosbyrevealingtheuseofiron-gallinkinthe

under-drawingofseveralpaintings.Thisisparticularlyrelevantbecause

althoughhistoricdocumentalsourcesrefertotheuseofiron

gall-inksfromaboutthethirdcenturyBCandalthoughsomestudieson

15thand16thcenturyeaselpaintingshavepointedoutitspossible

useinunderdrawing,itistheﬁrsttimethatithasbeen

unequivo-callyidentiﬁedin16thcenturyeaselpainting.

Furthermore,itallowedustoexplainthepreviousdiscrepancies

ontheunderdrawingofthisMasterworkshopthatwerepointed

outbyarthistoriansthroughobservationofIRreﬂectographies,

concludingthatthisMasterhadtwotypesofunderdrawing:avery

strongandmarkedunderdrawinginoppositiontoaverylightand

almostimperceptibleone.Itisnowclearthatthesediscrepancies

areduetoachoiceinmaterials(charcoaland/oriron-gallink)rather

thanadifferenttechnicalorstylisticapproach.

Thisstudypointsoutfortheneedofdeveloppingmoreadvanced

methodologiesinthestudyofunderdrawing,particularlywhenno

signalorweakresponseisgivenbyIRreﬂectography.Foriron-gall

inkunderdrawing,thebestresultsareobtainedbyIRphotography

atlowerwavelenghts.

Thisresearchcouldalsoleadtothereﬁnementofmethodologies

andtechniquesofexaminationforunderdrawingstudies.

Acknowledgements

Theauthorswish toacknowledgetheFundac¸ãoparaa

Ciên-ciaeTecnologia(PortugueseScienceandTechnologyFoundation)

forﬁnancialsupport(PhDgrantSFRH/BD/66068/2009andproject

ONFINARTS ₋ PTDC/EAT-HAT/115692/2009) through program

QREN-POPH-typology4.1.,co-participatedbytheSocialEuropean

Fund(FSE)andMCTESNationalFund.Theauthorswishtothank

totheHERCULESLabandJosédeFigueiredoLabteamsforall

sci-entiﬁccollaborationparticularly,SoniaCostaandLuisPiorrofor

aidinginthe surfaceexams.The authorsalsowish tothankto

theÉvoraMuseumandNationalAncientArtMuseum(Lisbon)for

grantingaccesstothepaintingsanditsstaff,inparticulartoart

historiansJoséAlbertoSeabraandJoaquimCaetanoforarthistory

collaborationandconservatorsSusanaCamposandTeresaMoura

fortechnicalsupportduringpaintingshandlingandanalysis.

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