The Production of a Lead Glaze with Galena

Accepted Article View metadata,citationandsimilarpapersatcore.ac.uk

system 70 wt. % PbO – 30 wt. % wt. SiO – 30 % PbO wt. 70 system equivalent the of those to compared and (HT-SR-XRD) Radiation Synchrotron with experiment % SiO wt. 25 – % PbS wt. 75 glaze withgalena,yet been investigated.not has Temperature transformations system forthe system has been studied for years, the PbS-SiO 18 ofthe beginning the from glazes lead of production the in used widely was PbS, as known also Galena, Article type : Article PROFESSOR TRINITAT PRADELL 0000-0002-8720-5492)(Orcid ID: DR MOLERA JUDIT (Orcid :0000-0003-3116-0456)ID This article This protected byis c cite this article as doi: 10.1111/jace.15346 whichmay lead to differences betweenthis version and theVersionof Record. Please beennot throughthetypesetting, copyediting, pagination proofreadingand process, This article hasbeen accepted for publication and undergone peerfull reviewbut has formedas soon asgalena decomposes during heating. the results The show that the system 3 1 Dpt. Mineralogia, Petrologia iGeologia University ofBarcelona, Aplicada, MartíFranquès, i s/n - 08028 U. Science Tech, MECAMATgroup, University of Vic-Central Universityof Catalonia-, de laLaura 13, The production of a lead glaze with gal Roberta Di Febo Roberta Di 4 Escolad'Art dei Superior de Vic, Rambla 24,Disseny Domènec,de Sant 08500, Catalonia Vic, 2 Physics Department, Physics campusBaixLlobregat,UPC-BarcelonaTech, Department, 8, EsteveTerrades 08860, 5 ALBA Synchrotron LightALBA Synchrotron Source, Cerdanyoladel Vallès, 08290, Barcelona, Catalonia Corresponding Author mail id:[email protected] 1 , JuditMolera th 20 the of half second the to century 2 are investigated in a high temperature resolved X-ray Diffraction opyright. All rights reserved. reserved. All rights opyright. 1 , Trinitat Pradell Castelldefels, Catalonia 08500, Vic,Catalonia Barcelona, Catalonia 2 SiO . Lanarkite, PbO·PbSO Lanarkite, . Abstract Vallcorba 2 system system ena: thermaltransformationsin thePbS- 2 , JoanCarlesMerlgarejo

2 phase diagram, involved in the formation of a of formation the in involved phase diagram, 5 th SiO the Although century. 4 , is the phase predominantly phase the predominantly , is 3 ,

Josep Madrenas provided byUPCommons.PortaldelconeixementobertdelaUPC

4 , Oriol Oriol , 2 -PbO brought toyouby CORE Accepted Article KEYWORDS: PbS-SiO brown coloursmetalimitated and forms. sand using compounds lead ora alone of leadmixture compoundsplus powdered or quartz were twoprimaryThere ofapplying methods lead glazesceramic to surfaces: either by (Han dynasty and Greco-Roman world) dynasty Greco-Roman (Han and PbO, 30 wt. % SiO % 30wt. PbO, glazesclose High(with lead composition % PbO). mixture totheeutectic 70 % wt. tocover of BC), large relatively of but were (<20 quantities comprised low jars, lead wt. 475-221period, states (Warring inChina lead glazesproduced containing were first The between the2 firing conditions in light of the high temperature transformations previously obtained. previously transformations temperature high the of light in conditions firing the and used mineral galena the of the composition of interms anddiscussed determined mattheddleite and lanarkite galena, of presence The studied. Pb PbO-PbSO the melts aat temperaturehigher thePbO-SiO than article This protected byis c confers brilliance to the glaze. excellentcrazing) and covering They capability. also have high a refraction index that which match those of earthenware giving them (minimal good adherence flaking and point, meting low viscosity and surface tension and a thermal expansion coefficient porcelain to make them waterproof. themmake to porcelain Lead glazes are among the earliest glazes usedto earthenware,coat stoneware and Introduction I. 2 . The. former method wasused betweenthe 1 2PbO·PbSO 4 nd -PbS system. A historical misfired lead glaze produced with galena is also and 4 and 2 4 , which melts at 717º C) were not produced until the 1 untilthe produced were not 717º C) at melts which , , 4PbO·PbSO th centuries 2 system, PbO-SiO opyright. All rights reserved. reserved. All rights opyright. 1

AD 4 mattheddleite, high stability thermal lead glazes, mattheddleite, 4

. One further variation was the was One variation further . Lead glazes have a wide processing range, low processingrange, Lead glazesawide have 4 2-3

. All these glazes show green, yellow and 2 system, but far lower than those expected for expected those lowerthan system, far but 2 system, galena, PbO·PbSO galena, system, st and 3 and rd centuries AD the latterand centuries 10 fritting fritting (SiO st 4 ) century BC 3.5 4 lanarkite, of the leadof (SO

4 ) 2 Cl 2, 2, is Accepted Article advantage. This does not occur inthe PbS-SiO of leadof sulphates andoxysulphates; PbO·PbSO not have acommon boundary itwill inthephase alwaysdiagram, involve formation the available melting point (717º (717º C point melting diseases shared by potters, guilders and glass makers to lead poisoning. until the 18 the until theof glaze. processgalena However, producinglead wasnotdocumented use of the a advantage obtain ingalena eliminatingthe to of oxide) lead (theroasting onestage of have would galena of use The times. Roman lead in the glaze production of the in (PbO) galena orroasted galena demonstrating of evidence use archaeological or literature the lead, no but is metallic toobtain there silver and toextract Romans by the PbS, leadGalena, the ore, is important and most widelyknown tohave been exploited used in the Medieval period until times. modern compounds-plus-quartz mixture before its application to the ceramic surface. the ceramic before to application its mixture compounds-plus-quartz article This protected byis c The main advantage ofthe PbO-SiO Although there is a detailed phase diagram for the phaseAlthoughPbO-SiO isadetailed diagram the there for information about the transformations that take place that transformations the in thePbS-SiO take about information SiO with SiO reaction the C) and breakdown 880º (above sulphate anion implies oxidation of the PbS PbSO of oxidation into implies silica the alimitedknown tohave Therefore, solubility the in melt. use of complementary information of the Pb-PbS, PbS-O and PbO-PbSO materials (lead compounds, plant ashes, alkaline salts, etc) ashes,plant salts, alkaline compounds, (lead materials any glassy glassya mixture firingor partially obtainedafter material of sand withflux 2, for which a melt forms at a relatively low temperature, below 760º C temperature, below relativelyat which low amelt for a forms 11-14 th . Theuseof century 6 . At. sametime the as Ramazzini, an Italianphysician, thelinked 10 ). ). The large range,compositional between 20 and 60mol. % galena opyright. All rights reserved. reserved. All rights opyright. implies the oxidation of PbS, but as PbS and PbO do PbSandPbO butas do PbS, of oxidation implies the 2 system in the production of glazes is its low glazes of is production in the system 4 and progressively more oxidised oxidised oxysulphates,and progressively more 4 , 2PbO·PbSO , 2 system. The PbS-PbSO The system. 5 . This method widely. was 2 4 system , 4PbO·PbSO , 2 2 to theobtain melt. system. However, 7 8,9,10

4 systems is 4 , there is there is no, 10 -PbO phase 4 which are which is also an 1 A galena frit is

Accepted Article France). The setupexperimental consisted of asmall cylindrical furnace with theraw ESRF the ID15B (Grenoble, at beamline keV)synchrotron high-energy (90 brilliance, The The the originand mineral sampleobtainedwas the frommineMolar (Catalonia). The production of a lead glaze with with lead glaze of a production The 916º C. diagrams show higher thetemperatures, melting lowest thefor moreoxidised species at article This protected byis c SiO the PbO (Fluka ref. 11526)andSiO PbO (Flukathe ref. caseusing and inthesecond case. PbOinone usinggalena reagents Chemical both for diagram of the PbO-SiO the of diagram withRadiation (H Synchrotron experiment for the PbO-SiO the for necessarily resolved during experiment. reached thetime the Therefore, obtained data the resultsobtained. glazesoflight of leadare limitationsgalena discussed production in inthe and its use of the reasons for the Finally, glaze. of the composition of the experiment and temperature discussed presence their identified and terms dataobtainedfrom ofthe Highin the crystalline phases present glaze the in vestigesincomplete from glazean firingare A historical misfired leadglaze ware that retains duetonon-equilibrium conditions.temperatures Two mixtures of the eutectic composition 70 wt. % PbO : 30 wt. % SiO % wt. of the wt.: 30 %PbOeutectic composition 70 Two mixtures Procedure Experimental II. (1) 2 in situ in situ system are investigated in a time re time in a systemare investigated

High-temperature resolved XRD experiment (HT-SR-XRD) (HT-SR-XRD) XRD experiment resolved High-temperature high-temperature were measurements obtained X-ray diffraction high-on the 2 mixture will reveal any shift in the phase transformation and melting and in phasetransformation the any reveal will shift mixture 2 system is well known, equilibrium conditions are notconditions are known, equilibrium well is system opyright. All rights reserved. reserved. All rights opyright. galena 2 (Merck ref. 107536) were selected. ref. 107536) were of Galena is (Merck T-SR-XRD). AlthoughT-SR-XRD). the equilibrium phase , PbS-SiO , solved high temperature X-ray Diffraction Diffraction X-ray temperature high solved galena 2 system, and the equivalent PbO- equivalent the and system, relic grains is also studied. Therelic isalsostudied. grains 2 were prepared were Accepted Article MgOcrucible, gives and qualitativeaof temperature evolution compound.each principal of intensity the relative the of peak each tothe phase crystalline of intensity The radial integration of the images was performed usingsoftware. Fit2D performedimagesthe was the integration radial of The were conditions.using standard determined same detector under the asilicon measured the and orthogonality of centre beam distance, detector to sample of the calibration The Themeasurement whole cycle took 3h. 10°C/min. rateof a at temperature sample wascooled downtoroom the Finally, 25°C. andthen readout, theimage erasure resulting in of plate), beingimages every taken time, cycle each 5min(measuring whole datasettook 4 in took total. The min for plate image- the of readout, anderasure data collection, Thecollection. data of the end the onlymin and ofvariation took 1 consequently a 5°Cthe between existed beginning and time Themeasuring ramping. slow duringthis datarecorded beingwith temperature maximumwas aconstant heating of heated 5°C/minafterwards at rate uptothe sample The 5minutes. between 90°–110°Ctemperature for the andthenmaintaining dryingAn initial consisting stagewas programmed, (1°C/min) aslow heating of rate The furnace temperature wascontrolled by apreviously external calibrated regulator. min and rotation of the sample was sufficient to ensure good data quality. Norderstedt, Germany) was used to collect the XRD patterns withan exposure time of 1 Animage-plate MAR345, for alignment. (Model detector goniometer Marresearch, on mounted MgOain 0.5-mm-diameter contained powders unsealed capillaries article This protected byis c SiO PbO- (a) identified for phases crystalline ofthe stabilityranges Thermal mixtures. the highXRD patterns represents temperature Cent theInternational from (PDF) database compounds Fileof was performed the based onthePowderDiffraction Identification 2 and (b) PbS-SiO and 2 are shown in Figure 4. The shown is ordinate 4. axis inFigure are the from obtained opyright. All rights reserved. reserved. All rights opyright. (HT-SR-XRD) obtained during the firing of the during obtained (HT-SR-XRD) re for Diffraction Data (ICDD). Fig.and 23Diffraction Data(ICDD). re for 15

Accepted Article (INCAPentaFETx3 detector, 30mm detector, (INCAPentaFETx3 an EDSdetectorcolumn with Shottky emitter witha Field equipped Neon 40) present.workstation compounds Acrossbeamthe crystalline (Zeiss identify EDS) to Electron Microscopy anEnergy with Dispersi mic petrographic reflected light usingand a Thethin sectionobtained. bywas studied was thickness ofandglazebody thin a standard 30µm section of ceramic to A polished different colours:different opaque green,opalescent yellow honey transparentand ( uncontrolled and unequal temperature conditions thekiln, inthe glaze exhibits three an ancient hospital building provided assistance, that medical Duein Vic. to was part of an assemblage of coarse wares found in the garret of of inthe garret found assemblage wares of an of coarse was part A misfired storage jar (CCV050) the dating from storage jar 18 A misfired (2)Analysis ofalead glaze misfired article This protected byis c ceramic interface asceramic interface well asthe crystallites. the glaze the of composition glaze-Finally,avoiding wasdetermined chemical the used were PbS for galena and Pb, SrSO Pb, and PbS galena for were used were 20kVconditions and 15nAwith a focused analysis). (spot beam The standards standard and averagethe and acquired were spectroscopy)of three detector.minimum A analyses crystallites the of andof theglaze which requires the high energy provided byresolution WDS the (wavelength dispersive S Pband present both contained that micro-crystallites different the of composition Electron Microprobe (EPM, JEOLwa JXA-8230) voltage. wereto crystallites carriedthe composition 20kV ascertain out at the acceleration SEMBackscattered investigation. electron(BSE) images were obtained and analyses of opyright. All rights reserved. reserved. All rights opyright. 2 , ATW2 waswindow) employed ATW2 , attached the for 4 for S, CaSiO S, for roscope (LEICA DM 2700 P) and Scanningroscope(LEICAand DM2700P) Optical Microscopy (OM) transmittedwith deviation deviation were obtained. operatingThe ve Spectroscopyve detector attached (SEM- s also used quantifyto thechemical th century was investigated 3 for Si and Ca and Cl. SiAgCl andCa for for Casa Convalescència Figure 1 6 . The . The jar ). , Accepted Article focused-beam station of beamline BL04 of beamline station focused-beam (SR- micro-X-ray diffraction Radiation PbO : 30 wt. % SiO % wt. 30 : PbO diffractionhigh temperature The data duringtaken heating amixturethe of 70wt. % The crystalline structure of the micro-c the of structure crystalline The article This protected byis c software. Fit2Dimages withthe of the performed was integration radial the and standard 15x15 geometry a measured with in transmission and system interest of thefrom polished thin section were selected using anon-axis visualization SiO corresponding diffractionThe during data hightemperature heating taken the PbO- of III. Results (ICDD). File(PDF)database theDiffraction Internationalfrom Data Diffraction Centre for beam of KeV 29.2 ( beam (1) PbO-SiO seen. pe the to XRDpatterncorresponding the heating, the during compoundsformed crystalline new and initial the from Apart shown. takenbe The HT-SR-XRD patterns respectively. LaB wasperformed usinga detector the orthogonality of andcentre beam distance, 79 pixels, detectorRayonixCCD SX165(active of 165mm area diameter, size2048 x frame 2 and PbS-SiO and 15 μ Identification of the compounds was performed based on the Powderthe on based wasperformed compounds the of Identification m pixel size, dynamic range 16 bit). The calibration of the sample to detectorto sample of the The calibration 16bit). range size, dynamic pixel m 2 high-temperature resolved XRD experiment experiment XRD resolved high-temperature 2 2 mixtures are shown in2D are in images mixtures is shown in λ = 0.4246 Å). The diffraction patterns were recorded with a patterns wererecorded diffraction The Å). =0.4246 opyright. All rights reserved. reserved. All rights opyright. Figure 2 Figure μ 16 XRD) on the same polished thin section in the sectionin polished thin same the XRD) on at the ALBA Synchrotron (Spain). Theareas atthe (Spain). ALBASynchrotron and the appearance disappearancetheand the and of rystallites was determ was rystallites riclase (MgO) from crucibleis the also fore heating and after cooling andafter alsofore heating are Figure 2 Figure μ m ined by Synchrotron ined by 2 (FWHM) focused focused (FWHM) and Figure Figure 3 6

Accepted Article increase in the range 715-722º C, just when Pb disappeared at 727º C. At 670º C Pb C At 670º 727º C. at disappeared C; increasinguntil 690º itformed decreased 715º C quickly completelyat and anglesite (PbSO (PbS), determined were galena compounds initial The phases marked. also are SiO % wt. PbO : 30 % eutectic composition70 wt. the equivalent acomposition to with quartz %of 30 wt. plusgalena %of 75wt. of a mixture for dataobtained diffraction temperature high The Finally, PbSiO Finally, completely at 795º C. A melt coexisting with other crystalline compounds appeared atcompounds crystalline appeared coexisting A withother C. melt 795º completely at was stableGalena began upto C 315º and then until toslowly disappears decrease it in is summarised identified phases were present in a very small amount. The thermal stability ranges of the crystalline and galena natural deposit, the of weathering compounds are cerussite anglesite and The reversible transformation between between transformation reversible The in summarised is quartz (SiO quartz Pbcm)initial and compounds massicot The orthorhombic, are phases marked. (PbO, article This protected byis c (2) High-temperature resolvedXRDexperiment PbS-SiO (a melt (a melt is expected to form at717º C compounds crystalline coexisting withother 722º C. Amelt at disappeared completely 2 Figure Pb was about C. As found clearly at 722º soon asPbOreacted withSiO 2 SiO 4 and PbSiO . PbO was stable up to 560º C. At 600º C, PbO began to decrease until it until to decrease C,beganPbO At600º to 560º C. stable up was PbO . 2 , trigonal). The thermalstabilitytrigonal). range thedifferent, compoundsof identified 3 was formed at625º C completelydisappeared and at727º Cwith an 4 ), cerussite (PbCO cerussite ), Figure 4a. 3 . 2 isshown in opyright. All rights reserved. reserved. All rights opyright. Figure 4b. 3 Figure 3. 3. Figure ) as well as periclase(MgO)well ) as Both crucible. the from 10 10 4 SiO in in the system 70 %PbOwt. – % 30 SiOwt. α -SiO 6 was formed and disappeared at 722º C. disappearedat 722º and was formed

The appearance and disappearance ofthe 2 and 4 SiO β 6 -SiO decomposed incongruently into incongruentlydecomposed 2

2 at 573º C, is in573º observed C, at 2 , Pb 2 SiO α -quartz, 4 was was α 2 - ) Accepted Article during the roasting of galena C at 600º roasting galena during the of The of leadappearance PbO·PbSO The oxy-sulphate, ( a loweralreadyanglesite temperature at had fullydecomposed C completely disappearing at 950º Minium (Pb disappearing950º C. C completely at fact, already present in the original galena ore although during ore wasformed original also galena already some presentinthe fact, In summary, the oxidation of galena ( oxidationof the In summary, 2PbO·PbSO lead dioxy-sulphate, suddenly Canda Lanarkite at795º C. disappeared 775º quickly 315º C)increasing (above progressively,galena butmore C between 595º and 900º C forsterite (Mg C forsterite 900º SiO about 775º C (a meltis expected 717º at C in the system 70 wt. %PbO – 30 wt. % article This protected byis c According tootherstudies afterwards decreasingdisappearedat itcompletely860ºafterwards when The reversible C. Anglesite was stable up to575º C, increasing between 575º C and 775º C and appearedat315º Cincreasing to 475º Cand up completely disappearingC. 595º at Cdecreasing275º Cupwards 275º from anddisappearing 315º C. Massicot (PbO) at transformation between between transformation to thePbO-PbSO developed;according infact, Meanwhile second C. not a melt at900º wasfound C and during the oxidation of of galena during oxidation the and 4PbO·PbSO the magnesia crucible. After cooling, the crystalline phases found werephases2PbO·PbSO the found crystalline cooling, magnesia After crucible. the of lanarkite, anglesiteof and 2PbO·PbSO 2 ) 10 . . With regard tothegalena weathering compounds, cerussite was stable up to 4 formed. Theleaddioxy-sulphate, 2PbO·PbSO formed. 4 4 -crystallising from the sulphate quartz melt-, (Mg and forsterite phase diagram a sulphatephase appear melt this a temperaturediagram should at 2 SiO α 4 -PbSO ) wasalso formed due reaction of tothe silicathe melt with opyright. All rights reserved. reserved. All rights opyright. 14 , lanarkite is actually the phase predominantly formed phase actually the lanarkite is , 11 . However, this is only true at very However,temperatures. this only. is at true low 4 and and Figures 4 and 5 β 4 6 . In theory anglesite is the first phase formed phase first is the anglesite In theory . . In the our case, . anglesite determined was, in -PbSO 4 at 883º C did notthe 883º Cdid occurbecause at 4 (lanarkite) 3 O 4 ) gave rise mainly to the the formation to mainly rise ) gave ) formed between 810º C 860º between and 810º ) formed 4 17 began to decrease at 900º 900º at decrease to began , followed, the decrease of ≈ 860º C) in our system. our 860º C)in 2 SiO 13 . At 4 ). ). 4

Accepted Article present inpresent three the coloured areas of the glaze, euheor elongatedthe sections of share tabular yellowglazes, the similar composition to Type composition similar I crystals, images, show tabular or elongated sections of euhedral crystals. They also have a diagram melt; this is consistent with thePbO-PbSO with consistent this is melt; stable below 863º C.stable below on further oxidation, 2PbO·PbSO lanarkite and on further glaze, glaze, S ( Pb and th in observedcrystallites are types of Three respectively. areas yellowgreen, and coloured honey BSE images corresponding the to opalescentgreen, yellowish and transparent honey, dis three lead glazeexhibits misfired The of (3) Analysis lead a glaze misfired complete oxidationgalena of intoPbOwasnot obtained during heating. the the decomposition of galena between 600º C and 800º C. The PbO-PbSO C. The 600º Cand800º between galena decomposition of the article This protected byis c cooling, twoleadcooling, 2PbO·PbSO oxy-sulphates, During was the inturn atC decomposed was formed whenamelt 950º formed. which lanarkite decomposedlanarkite at795º C dioxy-sulphate completely lead the while 2PbO·PbSO PbO-SiOour case, a in contrast,formed. In is liquid C whenasulphate 928º completely at ~860º C.completely the at Inaddition, PbO-PbSO already at developed a lowertemperature, Cand ~775º anglesite disappeared Figure 1(a).Figure 11 indicates that that indicates both PbSO Figure 1d Figure Figure 1(a,b) Type II crystals, which appear slightly darker in the SEM BSE SEM in the darker which slightly appear IIcrystals, Type ). Type I crystals appearing light grey are found only in the green the only in grey found appearing light are crystals I Type ). 11 In fact, In the presence ofthese lead oxy-sulphates indicates that a opyright. All rights reserved. reserved. All rights opyright. . Type III crystals show a similar light grey colour and grey light colour similar a show IIIcrystals Type . 4 and PbO·PbSO and Figure 1(d)Figure 4 tinctive areas of different colours:opaquetinctive ofdifferent areas e three areas and all of them contain mainlythem contain all of three areas and e phase diagram where both compounds arewhere bothcompounds phasediagram 4 dral crystals as found in Type They II. are and 4PbO·PbSO and 4 shouldcoexist. However, in ourcase, Figure 1 4 and are found in both the green and green both the in found are and diagramphase also indicates that, Figure 1 4 , are stable at temperatures below . Figure 1(a-c) Figure . However, chemicalthe 4 recrystallized thefrom shows SEM SEM shows 4 phase 2 melt melt 4

Accepted Article PbO·PbSO by identified SR- are IIIcrystallites Type Type IIand galena. Type containI crystals wt.86.1 %Pb 13.6and wt. %S andnoO, corresponding to PbO·PbSO for obtained Type the II crystals is in also good agreement with those lanarkite,of 1.2 % ZnO, 1.1 % FeO, 0.5 % Na %FeO, 0.5 1.1 % ZnO, 1.2 Pb composition theoretical of supergroup (ellestadite) theapatite of mineral a rare contains lessCl, some Ca unexpected unbalanced mattheddleite fact,and is S. Siand In Pb crystallites (Ca crystallites composition of the glaze in wt. % is 73.5 % PbO, 19.6 % SiO 19.6 % PbO, is 73.5 % wt. in the glaze of composition a superior X-ray peakresolution and greater peak tobackground ratio. The chemical withsystem (WDS) detector Spectroscopy X-ray Dispersive a Wavelength usingEPM, Consequently, the chemical composition ofthe crystallites and the glaze is obtained by because of the large overlapping of S-K Quantitative chemical analysis ofthe crystallites possible with not is the EDS detector images. BSE the in contrast atomic similar a show Type III, II Type and Crystallites, Pbmainly andS. but also some Cl, and minor ofamounts Si and Ca, they tothoseof Type isslightly Type III of different II; containcomposition crystals article This protected byis c by EPM wasalreadynoticed calcium alsobemay incorporated structure. inthe unbalanced The Si S and measured standard deviation of the various analyses made on the crystallites are shown in shown are crystallites the onmade analyses the various of deviation standard Ca and fluorellestadite composition theoreticalhydroxylellestadite of 5 10 5 (SiO (SiO (SiO 4 4 4 ) ) 1.5 ) 1.5 3.5 4 4 . Conversely, the chemical composition determined for the Type III the for determined chemicalcomposition Conversely, the . silicatelead chloride sulphate mattheddleite, a and , (SO (SO (SO 0.04 4 4 4 ) ) ) 1.5 1.5 ,Pb 2 Cl (Cl,OH) (OH) andCa (OH) 2 0 . respectively, as shown in 96 ) 10 (SiO 21 opyright. All rights reserved. reserved. All rights opyright. ; other of thisthe endmembers group are 4

) 4 and associatedand tolarge inaccurate absorption 2 (SO O+K 5 (SiO 4 ) 2 2 O, 0.2 % CaO, and 0.05 % Cl. The average and Cl α 4 , Pb-M ) 0.8 1.5 , differ from the theoretical composition; theoretical the differ from , (SO Figure 6 Figure 4 α ) and Cl-K and 1.5 F respectively. . The chemical composition. α 2 , 1.5 % Al X-ray fluorescent X-ray fluorescent peaks. 18-20 μ XRD as lanarkite, lanarkite, as XRD 20 of composition Consequently, 2 O Figure 1(d) Figure 3 , %SO1.5 , Table I Table 3 . . , Accepted Article and 1 has straight extinction while mattheddleite 0.108), = (birefringence extinction inclined Although both, lanarkite and mattheddleite crystallites are present in theopalescentlanarkite present crystallites andmattheddleite in are Althoughboth, colour. The concurrence of galena and Fe and galena The concurrenceof colour. corrections occurring when celestite is usedas S standard article This protected byis c and, and, consequently, show the yellow tinge characteristic of Fe exposedbeen have would not transparent-honey areas andthe opalescent-yellow The flame. the surface glazed to the exposure of mightbethe atmosphere reducing this for delayedthe decomposition galena of the reductionand the Aof ironions. possible cause s The firing. atmosphere duringreducing the glaze. glaze. gangueThe also included some sphalerite grains thatexplain the presence ZnO thein (glaze) particularityduringenvironment and, crystallisation some incorporated calcium. integrated available thesurroundingelements mattheddleite of from inclusions the neo-formed Inourcase, EPManalysis. other mattheddleite with agreement crossed polarized light (XPL); lanarkite displays2 crossed polarized light (XPL);lanarkite some grains. of exfoliation Lanarkite and 7c, Figure ( microscope optical Under the presence of Fe grains of galena accounts honey. occurrence The transparent theopacityfor andthe appearances coloursand ofthethree areas: opaque green, translucent yellow and differentcrystallites in of presence The showslanarkite relief and darker a contrast than mattheddleite, tabular somelanarkite addition, show light, sectionsreflected In of polysynthetic twins. st

andlow 2 by its high reflectance and because of thefractures byofreflectance andbecause high its cubic planesalong of the 2+ ions dissolved in the glaze ionsdissolved the ismost in nd order interference colours (birefringence = colours(birefringence orderinterference 0.018), opyright. All rights reserved. reserved. All rights opyright. Figure 7 ) galena is easily recognizable in reflected light, reflected in recognizable is easily ) galena the glaze is responsible for the various various forthe the isresponsible glaze 2+ hortage of oxygen is responsible for both, for isresponsible oxygen of hortage is explained by the glaze toaby explained exposure the is mattheddleite canmattheddleite bedistinguished with nd probably responsible for the green the responsiblefor probably /3 rd order interference colours order and interference 21 .

In fact, ourdatais ingood Figure 7 (c) 3+ and of lead glazes. glazes. lead of and Figure 7b Figure . . In Accepted Article On the other hand, based on the PbO-PbSO the hand, based on other On the our data,match supporting of thevalidity ourdata. kinetic and decomposeform compounds different the which temperatures at the Moreover, incongruently. Our high temperature experiment isin perfect agreement with this. only PbSiO related to the presenceof tothe SiO related PbS-SiO the in lanarkite disappearance sudden The of C. 795º suddenlyat disappearing crystallization of the PbO/SiO the of crystallization is probably toremaining due insulphates the glaze mixture thethat handicapped the formation of lanarkite (PbO·PbSO lanarkite of formation the Although the first experimental studiesof the PbO-SiO Although first the Discussion IV. adamantine lustre. however, contains only mattheddleite crystallites, which are transparent and show an macroscopicallylustre appearing pearly yellow lanarkitearea, crystallites are responsible theopalescence, for as they have a article This protected byis c et al.et of of compounds with PbO:SiO In the PbS-SiO In the than 860°C, anglesite (PbSO 860°C,anglesite than first 2PbO·PbSO leads lanarkite which tothe subsequent to development ofoxidation tends form Further system happens at lower temperatures than in the PbO-PbSO the than in lowersystem temperatures at happens melt at at melt 23 found found PbSiOthat ~ 775º C. The775º C. yellow the misfired areas and of green glaze also showthe 3 , Pb 2 system 2 4 SiO and then3PbO·PbSO 4 and Pb

studied, 3 and Pb and opyright. All rights reserved. reserved. All rights opyright. 4 4 2 2 SiO 2, ) and lanarkite (PbO·PbSO ) andlanarkite moleratios of 4:1, 3:1, 2:1, 1:1, and 5:8 were formed; compounds. The oxidation of galena gives rise mainly to mainly gives rise galena of The oxidation compounds. whichto aPbO-SiO certainly giving arole, plays rise

lead silicates are notformed. The lack ofleadsilicates 6 were confirmed by research. confirmed were other 2 SiO 4. 4 melt congruently while Pb while congruently melt 24 4

) at a temperature low) as atatemperature as translucent. The transparent-honeytranslucent. The area, 4 phase diagram phase 2 system 4 ) are the two stable phases. two stable the ) are 13 13 9 for temperatures lowerfor temperatures 4 indicated that aseries that indicated system. This can be 4 8,22 SiO Moreover,Jak 6 decomposes ~ 315º C 2 2

Accepted Article found inside inside found mattheddleite in crystals the green areaof the glaze, crystals, surrounded by lanarkite found Galena is glaze. shows section thin cross sequence of sulphate the the formation of inthecompounds The chlorine. of presence the by driven is formation its anglesite and and lanarkite with atoms, identified. is Mattheddleite occurs in oxidizedzones oflead deposits, associated mattheddleite Pb mattheddleite transparentConversely, nor honey the However,lanarkite. glaze galena shows neither areathe of galenain affected oxidationand the andlanarkite glaze. the the formation of we Therefore, can also suppose that the lack of oxygen to thedirectdue hit of the flame misfired presenceindicateareas also the of reduced andoxidised iron respectively. green sulphatesulphur oxidation decomposition. The and and yellowcolours the of Moreover,short firing. the flame also produ glazemisfired indicates not onlyfiring alow theleadlanarkitethehistorical in area thepresence and of both galena In glaze. fact, of lanarkite decomposition in thehigh temperature areexperiment, not found in honeythe The two basic lead sulfates, 2PbO·PbSO sulfates, lead twobasic The inpresent thegalenaused by potters. ancient misfired glaze. Therefore, absence of anglesite be an could indicative that wasit not up tostable and, is consideringproduct it that Anglesite in often present is temperatures. of silica presence melt a and lanarkite, butnot higherthe compounds formed at article This protected byis c galena mineral orthere during Averypopular lead was contamination mineral galena firing. the the of in the part glazes; sources it two foundpossible theformed for There are chlorine chlorine mattheddleite,then the is provided surrounding available in glaze. andlanarkite first is, galena of oxidation duringthe sequence compounds of formed the 5 (SiO 4 ) 1.5 (SO opyright. All rights reserved. reserved. All rights opyright. 4 ) 1.5 (Cl,OH), with some calcium substituting the with(Cl,OH), lead calcium substituting the some 4 and 4PbO·PbSO ces a reducing atmosphere, which delaysatmosphere, reducing ces which a the ore galena original as a weathering temperature (below 795º (below795º aC) butalso temperature ~ 860º C, it should be found in the in shouldbe found it 860º C, Figure 7 (a) Figure 7 4 which are formedwhichafter are the Figure 8 , while lanarkite is lanarkite while , . Therefore, Accepted Article The supposed disadvantage, initiallyconsidereddisadvantage, the PbO-PbSO supposed basedon The The transformations during the production of a galena with PbS-SiO leadglaze a production of during transformations the The V. Conclusions guaranteed. are conditions shows that in the system PbS-SiO Consequently, optimal firing conditions thePbS-SiO optimalfiring for Consequently, conditions place. process oxidative take the arenecessary conditions to help oxidation and that at 795º lanarkiteC the is already decomposed.fully Nevertheless, adequate slightly higher than thoseslightly of than the PbO-SiO higher rise to the formation of lanarkite, PbO·PbSO of lanarkite, formation the to rise six leadmines. mineral extraction site in Catalonia is the Begur Coast, alsoknown as the of coast the article This protected byis c could also explain the alsoexplain direc preferential could surface of the glazes. In fact, presencethe of ashes on theglaze surface during thefiring and honey areas of the glaze, the crystals glaze–from towards the surface body-ceramic yellowish observed inthe formation of a formation ( melt decomposition of sulphates highof thelead whichthe and at the diagram, temperatures burning generatedthehand, gangue. other On ashes in galena the the of chlorine presence available dataavailable for the PbO-SiO the to compared were and the obtained results determined were formed compounds the stability phasetransformations thermal of The and (HT-SR-XRD). Radiation by with meansof highstudied Synchrotron X-rayDiffraction experiment temperature a

halophyte typeplants 25 Themines oftenare flooded by which seawater, could explainthe ~ 928º C) happen is not correct for the928º C)happen system PbS-SiO not for correct is opyright. All rights reserved. reserved. All rights opyright. Figure 1(b,c) 26,27 2 and and PbO-PbSO during the during the tothefiring provide chlorine couldalso 2 at a temperature ata C low 775º as is as a formedmelt tion of growth shown by the mattheddleite the by shown of growth tion . 2 4 system adequateoxidative provided 4 , at 315º C decomposition at and its at, systems. The oxidation of galena gives gives galena of oxidation The systems. 2 system are a temperature onlya temperature systemare 2 . Ourdata. 4 phase 2 were Accepted Article Moreover, in agreement Moreover, the with PbO-PbSO Acknowledgements + glaze surface during the firing. plant onthe beexplained of the ashes bythedeposition towards could glaze surface Thecrystallization temperatures. of mattheddleite and its directional from growth the the sulphur of couldhaveflame delayed lanarkite indicatesand a reducing temperature of 795ºmaximum C, althoughthe action observed colours surface(mattheddleite) onthe of the sample. The presence ofgalena transparent-honeyand mattheddleite) and opalescent-yellow (lanarkite mattheddleite), and lanarkite (galena, green the opaque responsible are for crystallites The SiO prevent the formation of the lead silicates. The results obtained optimal results show of The the that theleadsilicates. formation the prevent attemperatures form above C. The 750º presence of lead sulphates inthe silicate melt firing conditions for the the PbS-SiO conditions for firing 795°C, a temperature lower than those found those PbO-PbSO lower found in the than atemperature 795°C, article This protected byis c lanarkite, PbO·PbSO lanarkite, compounds crystalline honey- different showing yellow andgreen, colourareas - identified. Different phases were developed crystalline lead A historical misfired glaze retaining ofgalena relics still was the studied also and in order to sulphur eliminate from the glaze. the PbS-SiO the basic sulfates, lead 2PbO·PbSO 2 system, but when galena is used, highly oxidative conditions need to be guaranteed tobe need conditions is used, highlygalena when oxidative but system, 2 system contrary to what is observed in the PbO-SiO 4 and mattheddleite, (Ca,Pb) mattheddleite, and opyright. All rights reserved. reserved. All rights opyright. 4 and 4PbO·PbSO and 2 system are, temperature a rather similar PbO- tothe 4 and oxidationsulphate even athigher system, once lanarkite decomposes, two of the glaze, were discussed.Galena, were glaze, the of 4 10 form. Lead silicates do not form in form do not silicates Lead form. (SiO 4 ) 3.5 (SO 4 ) 2 2 Cl 4 system they where system (916º (916º system C). 2 were identified. were Accepted Article Shanghai Res. Soc. Sci.Ancient Technol. Shanghai. Ceram., 1995;12-17. symposium on international ofthe Proceedings ceramics.ancient Edited Guo. byJ. and 2014SGR1661 (J.C.M.). project areto due 2014SGR1585(J.M.Thanks the 2014SGR00581(T.P.), andR.D.F.) (BL04).Facility 2014060905 ALBASynchrotron Light andthe (Spain) Innovación References 6 5 4 3 2 1 2017-2019 MAT2016-77753-R, project Central of University Vic, University of Di Febo Roberta to grateful is the UV article This protected byis c so-called ‘glass decoration.paste’ In and reasons for use. arqueológica i arqueomètrica a un conjunt de vasos ceràmics del segle In del XVIII. un vasos de ceràmics conjunt a i arqueomètrica arqueológica 11-22. 2007;Oxbow Books. Rehren. T. Freestone, C. Shortland, I. J. by A. Edited Technology. glazed In productions. From MinetoMicros late continuance into antiquity. andUniversity ofPensylva Gómez A, Gil C, DiFeboCasaR, Convalescència C, etal.Gómez A,(Vic, Gil Osona): Aproximació Molera J, Pradell T, Salvadó N, et al. Lead Frits in Islamic andHispano-moresque glazedlead technology Tite pottery Roman MS.Production and its of M, Walton A&C Wood N. Chinese chemistryBlack London Glazes, origins, re-creation. the and with pottery jar States aWarring examination of Apreliminary Freestone I. Wood N, Tite MS, Freestone I, Mason R, et al. Lead glazes in antiquity- Methods of production Archaeometry. nia Press, Philadelphia;1999. opyright. All rights reserved. reserved. All rights opyright. Archaeometry. 1998: 40, 241-260. Science and 3 Science of ancientceramics: technology

IC-UCC Scholarship Program, awardedbyIC-UCC Scholarship Program, funded by the Ministerio de Ciencia e Catalonia. The gratefulCatalonia. authors are the to 2010;52,733-759. cope: Advancescope: in theStudy of Ancient Actes . Accepted Article Society beamline beamline ALBAat Synchrotron. to Detector From Real Software: Thermal Analysis andCalorimetry. system. SiO2.jpg&dir=FToxid SiO2.jpg&dir=FToxid http://www.crct.polymtl.ca/fact/phase_diagram.php?file=Pb-Si-O_PbO- 17 16 15 14 13 12 11 10 9 8 7 Catalunya.2015; 70-81. Central Catalunya la de d’Arqueologia Jornades III article This protected byis c 1934; 13, 237-244. SiO 1988; 88, 78-84. Research. Research. Smart RM, Glasser FP. Compound Formation an FP. RM, Glasser CompoundFormation Smart Geller RF, Creamer AS, Bunting EN. Thesystem PbO-SiO LeadandleadPoisoning MA. Antiquity to Modern Times. from Lessler Billhardt HW. New data on basic leadon basic sulfates,data New HW. Billhardt Richemond WE, Wolfe, C. lanarkite. Crystallography of Kullerud G. The lead-sulfur system. Eric RH, Timucin M. Phase equilibria andthermodynamics in thelead-lead sulphide PbO-SiO diagram Phase Factsage, Fauth F, Peral I, Popescu C, et al. Th etal. Popescu C, I, Peral FauthF, Hanfland M, Svensson SO, P, Hammersley Abdel-Rehim, Thermal A.M. and XRD analysis ofEgyptian Galena 2 . J. Am. Ceram. Soc. Ceram. Am. J. ; 1970 J. S.J. Afr.Inst. Min. Metall. 1996; 14, 235-248. ; 117, 690-692. 1974; 57, 378-382. opyright. All rights reserved. reserved. All rights opyright. Powder Diffraction 1969; 88, 353-361 Idealised Image or Two-Theta Scan. 2006; 86, 393-401. 2 . American Journal of Science. e new Material Science Powder Diffraction d phase equilibria inthe d phaseequilibria system PbO- et al. Two-Dimensional DetectorTwo-Dimensional al. et . 2013;28, 360-370.. Journal of the Electrochemical the Journal of , Publicacions de Publicacions Generalitat , Am. Min. 2 , J. Res. Nut. Bur. Stand. Bur. Nut. Res. J. 1969;233-256. 267, 1938; . Journal. ofthe

High Pressure Pressure High 23, 799-804. Ohio J. Sci. J. Ohio

Accepted Article contains relics of galena (I) and neoformed crystallites II and III, (B) the translucent translucent (B) the IIand III, crystallites neoformed galenaof (I)and relics contains glazecolour areas. SEMbackscattering of (A) images opaque the area greenwhich The 1. Figure neck ofa century which 18th exhibit jar a misfiredglaze showing three Captions Figure temperature. temperature. MeV SiO 2016; 70, 265-280. Scotland. Leadhills, paragenetic sulphatesrelationsat of and sulphur analysis minerals. withphase the apatite structure. Leadhills,groupStrathclyde Region, from 27 26 25 24 23 22 21 20 19 18 article This protected byis c 1011-1018. 1011-1018. SiO Barcelona; 1990. Calvert PD, Shaw RR. Liquidus behavior in the silica-rich region of the system PbO-regionof the silica-rich Liquidus in behavior ShawRR. Calvert PD, Ponsot Ponsot B, Salomon J, Walter P. RBS study of thermal oxidationgalena inairwith the of ThermodynamicOptimization Jak al. E, PbO- Systems Wu et DegterovS, P, LivingstoneEssene missing Henderson EJ, CE, sulphurinmattheddleite, The A. supergroup of the apatite Nomenclature et C, al. Ferraris AR, M,Kampf Pasero Si S, a Pb, mattheddleite: of structure Crystal A. JJ, Livingstone Pluth IM, Steele Livingstone Mattheddleite,et al. newmineral EE, Rybackthe a apatiteA, Fejer of G, Misra M, Raglund K, Baker A. Wood ash composition as furnaceMisra composition A. a function of Wood ash M, RaglundK, Baker Lynggaard F. de Tratado cerámica. Omega, Ediciones Barcelona; 1976. Perelló, JMM. Els minerals de Catalunya, 2 2 , PbO-ZnO, ZnO-SiO . 16 J. Am. Ceram.Soc O 3+ European Journal of Mineralogy.of Journal European ion beam. ion Biomass Bioenergy Nucl. Instr. Meth. Phys. B Phys. Res. Instr. Meth. Nucl. . . 1970; 53, 350-352. 2 and PbO-ZnO-SiO and opyright. All rights reserved. reserved. All rights opyright. Min. Mag.Min. . 1993; 4, 103–116. 2000; Scottish Journal of Geology.of Scottish Journal 2010; 22, 163-129. 2010; 22, Edited by Institut Editedd’Estudis byCatalans, Institut

2 64, 915-921. . Metall. Mater. Trans. Trans. B. Mater. Metall. . 1998; 136–138, 1074–1079. 1987; 23, 1-8. 1977; 28, Min. Mag.Min. Accepted Article PbS-SiO mixturethe for stage firing final of the of HT-SR-XRD patterns Selection 5. Figure qualitative temperatureof evolutioneach compound. and givesintensitythe aMgOrelative phasethe to crystalline crucible, of each of Figure 6. 6. SR- Figure Figure Thermal stability 4. ofthecrystalline ranges phases identified for (a) PbO-SiO initial mixture and before heating(top) (bottom) after cooling alsoare shown. 70 wt. % PbO - 30 wt. %SiO wt. %PbO-30 70 wt. High 2. Figure during temperature XRD thefiring patterns obtained (HT-SR-XRD) of ofofthree types crystallites. the spectra EDS (E) III. only crystallites containing area honey the (C) transparent IIIand, IIand crystallites containing yellow area article This protected byis c the mixture % 75 wt. SiO % PbSwt. –30 mixture the High 3. Figure during temperature XRD thefiring patterns obtained (HT-SR-XRD) of shown. arealso cooling(top) (bottom) andafter heating before and (b) and PbS-SiO prismatic sections of lanarkite exhibit 2nd /3 of lanarkite sections exhibit 2nd prismatic andelongated the sections hexagonal extinguished: basal are the greyorder colour, light wheretheelongatedtransmitted section of themattheddleite crystals shows a1st XPL (b) (III); mattheddleite and (II) lanarkite of crystals transparent (I), galena of grains 7. OM Figuregreen images of the area glaze. (a) lightshowing PPLopaque transmitted and 00-041-0610 for mattheddleite. patterns marked correspond tothe JPDF 2 . μ XRD pattern of the ofthe incrystallitesglazes. misfired XRDreference the The pattern 2 . The ordinate axis is obtained from the intensity of the principal peak theprincipal of intensity the is obtained from axis The ordinate . opyright. All rights reserved. reserved. All rights opyright. 2 . The XRD patterns corresponding to the initial mixture initial tothe The XRDpatterns corresponding . database patterns 01-071-2069 for lanarkite 2 rd order interference colours; marked with marked colours; interference orderrd . The XRD patterns XRD The patterns . corresponding tothe 2

Accepted Article calculated bystoichiometry. crystallitesthe measured by N number EPM. of measured.crystallites The oxygen is 1.Table Average and standard deviation (inparenthesis) of the chemical composition of mattheddleite of acrystal inside lanarkite crystallite light a in OMimage of reflected 8. Figure compensator. lambda ¼ with light (II);(d)XPLtransmitted lanarkite than lower relief exhibits (III) mattheddleite veryreflectant, (I) galena appears light, reflected (c) twin; a arrow, an article This protected byis c

yeII 9 III Type yeI 8 Type II yeI 6 Type I t b S C C O Sum O Ca Cl Si S Wt% N Pb (0.3) (0.1) (0.3) (0.3) (0.3) (1.1) (0.2) (0.2) (0.1) (0.1) (0.2) (0.3) (0.1) (0.5) (0.2) (0.1) (0.8) (0.1) (0.3) 75.1 2.5 4.5 1.2 0.7 14.9 0.1 14.6 98.8 98.5 - 0.2 78.1 5.5 86.1 13.6 - - 99.7 opyright. All rights reserved. reserved. All rights opyright. Accepted Article

Accepted Article