The synthesis of red lead pigment (chemically lead oxide, Pb3O4) was carried out considering different starting lead compounds. The experimental procedure followed was established according to some recipes of ancient painting treatises and the knowledge of the phase transformation of lead oxides. The samples transformation was monitored by X-ray powder diffraction and selected samples were also characterized by scanning electron microscopy. The pure Pb3O4 phase was obtained for the transformation of PbO2 and 2PbCO3·Pb(OH)2. Morphological studies revealed that the material obtained from PbO2 presented the more homogeneous grain size distribution. The transformation of white lead Kremer Pigment resulted in a mixture of Pbr3O4 (major phase) and cerussite (PbCO3), leading to a sample with low crystallinity.info:eu-repo/semantics/publishedVersio

Carvalho, Ana P.

Cruz, António João

Gonçalves, Paula M.

Mendonça, Maria Helena

Pires, João

English

Repositório Comum

CHAPTER ELEVEN Theory vs practice: synthesis of red leadfollowing ancient recipesPAULA M. GONÇALVESJOÃO PIRESANA P. CARVALHOMARIA H. MENDONÇAUniversidade de Lisboa ANTÓNIO J. CRUZInstituto Politécnico de Tomar AbstractThe synthesis of red lead pigment (chemically lead oxide, Pb3O4) was carried out considering different starting lead compounds. The experimental procedure followed was established according to some recipes of ancient painting treatises and the knowledge of the phase transformation of lead oxides.The samples transformation was monitored by X-ray powder diffraction and selected samples were also characterized by scanning electron microscopy. Thepure Pb3O4 phase was obtained for the transformation of PbO2 and 2PbCO3·Pb(OH) 2. Morphological studies revealed that the material obtained from PbO2 presented the more homogeneous grain size distribution. The transformation of white lead Kremer Pigment resulted in a mixture of Pb3O4(major phase) and cerussite (PbCO3), leading to a sample with low crystallinity.IntroductionSince the time when the oldest known paintings where done, at least, red is one of the main colours. In prehistoric paintings red was one of the mostemployed colours, together with yellow, brown and black. In the Roman civilization the most expensive pigment was red pigment cinnabar, a luxuriousand prestigious colour extracted mainly from mines in Spain that, according toPliny (1st century AD), were the most defended place in the Empire. In the Chapter Eleven 202Renaissance, the cardinals’ robes begun to be dyed with the red obtained from the kermes insect, a decision that reinforced the importance of the colour.1In the western painting, until de development of the modern colourssynthesized in the context of the chemical research, red ochre (essentially, hematite or Fe2O3, obtained from earths), cinnabar (HgS) before the 8th century and, after that, vermillion (an artificial form of cinnabar) were the most employed red pigments. Another pigment with the same colour is red lead or minium (an artificial form of Pb3O4), but it was less used in general. However, it had some importance in the specific painting techniques of illumination. TheMedieval Latin verb miniare, that is, to write with minium, was applied to thered initial letters of manuscript chapters. It is from this practice that derives words such as miniature (English) and miniatura (Portuguese). In Antiquity,however, the name minium was not applied to red lead, but to other red pigments.2Under the name of sandarach, red lead was first mentioned in the westernliterature by Vitruvius (1st century BC), who said that it was discovered as the result of an accidental fire to which the white lead pigment (2PbCO3·Pb(OH)2,obtained from lead) was exposed. According to Pliny, this had happened inPiraeus, Greece. Until the 15th century, when an alternative process arises,through the simple melting and oxidation of lead metal, the preparation of red lead was done precisely by heating of white lead.3Among the published recipes for preparation of red lead there are tworecipes presented by the Portuguese writer Filipe Nunes in its Art of Painting,dated from 1615 but with significant influences in the Portuguese technical literature of the following centuries.4 In the first recipe, which, according to Nunes, is based in Andrés Laguna’s edition (1555) of Pedanius Dioscorides’s Materia Medica (1st century AD), he prescribed the following: “Form a bed of some very thin sheets of lead in the bottom of a new pot. Then make a layer of ground sulphur, then another of lead, continuing in this way until the pot isfilled. Put it on the fire, and mix everything with an iron rod. See that your noses are stopped because the vapour is very harmful”. In the second recipe, Nunes said: “Others use white lead in place of sulphur5. Covering the vessel very well, leaving only a small hole through which it may breathe, they put it in the oven until is very well burned. This is the best way”.6The preparation of red lead by heating of white lead, such as in Nunes’second recipe, is presented in many medieval and later technical sources. For instance, that procedure is mentioned in Mappae Clavicula (from about 800, but with additions from the 11th and 12th centuries)7 and Theophilus presbyter’s treatise (12th century)8, although none of these sources present details regardingthe employed conditions, with the exception that both recommend that white Chapter Eleven 203lead should be stirred during the heating process. Some details are presented inanother source. According to Audemar’s De Coloribus Faciendis (13th or 14thcentury), the jar with white lead should be “over de fire for two days and two nights” and the fire should be “of charcoal only without flame”. Moreover, “the stirring is the principal cause of the perfect preparation” and “must be repeated four or five times in the space of every two or three hours”.9 In another recipe, it is said that “the more it is burnt the redder it is, and the less it is burnt the moreit retains its former colour, that is, its whiteness or its paleness”.10In spite of the details presented by Audemar, it is not common to find detailsregarding red lead in ancient recipes and, consequently, it is probably that thepigment was manufactured differently in different places and time and, asconsequence, it is possible that red lead with different composition could have been used. Our main objective was, precisely, to investigate how some experimental conditions could originate materials with different composition. Lead OxidesChemically red lead is a lead oxide with lead presented as Pb(II) and Pb(IV). The lead-oxygen phase diagram includes a set of oxide compositions, as it is well known. According to different references11they have the following compositions: PbO, Pb3O4,Pb12O17, Pb2O3, among others. In the study of lead oxide decomposition it has been found that the process occurs in the temperature range 330-570 ºC, in stages, with the successive decreases of oxygen content, from PbO2 until PbO. It is known that lead monoxide has two polymorphous modifications: lowtemperature form -PbO (litharge), with tetragonal lattice, stable up to 490-540ºC, and high temperature orthorhombic -PbO (massicot). Endothermic phase transition is accompanied with small thermal effect (0.418 kJ mol-1). At room temperature the rate of the reverse transition is very low and the -phase can be stored in metastable state over prolonged time. An interestingobservation was made when the reverse reaction from PbO to Pb3O4 at slowcooling from 600 ºC in air was reported. In fact, Clark and Rowan12 report theformation of distorted ‘active’ -PbO after thermal decomposition of lead carbonate and hydroxide and its oxidation to Pb3O4 at temperatures below 400ºC.ExperimentalThe effect of the experimental conditions on red lead’s composition wasinvestigated starting from different materials containing lead and operating at different temperatures and heating times. The compounds used are listed in Chapter Eleven 204Table 1 where some of their characteristics are also presented, as well as their designation in the following text.Sample Compound Colour Crystal structureA PbO (Merck, >99%) yellow OrthorhombicB PbO (Merck, >99%) orange orthorhombic and basecentred orthorhombic  C PbO (M&B , >99%) orange orthorhombic and basecentred orthorhombic D PbO2 (M&B, >99%) BlackTetragonal and orthorhombicE 2PbCO3·Pb(OH) 2 (M&B,>99%) White RhombohedralKremer White Lead, Kremer Pigment White Orthorhombic and rhombohedralTable 1 – Starting materials used to prepare red lead. (The crystal structures were identified using the files of the International Center for Diffraction Data (ICDD).A four step procedure was carried out: two calcinations at 400 ºC followed by two calcinations at 450 ºC, always for 2 hours. Between the treatments the samples were grinded into a fine powder. The samples will be designated by thecaption letter correspondent to the starting compound followed by 1, 2, 3 or 4according with number of heat treatments made. Calcinations were done in amuffle furnace Nabertherm GmbH (Mod. L3/12/P320) equipped with a Controller P320. The synthesis process was monitored by X-ray powder diffraction (XRD). Patterns were recorded on a Philips PW 1730 diffractometer with automatic data acquisition (APD Phillips (v3.6B) software). CuK radiation ( = 1.5406 Å) was used as incident beam and a graphite-monochromater was employed. Diffractograms were obtained by continuous scanning from 15 to 80 º 2 , with a step size of 0.02 º 2  and a time per step of 0.4 s. The identification of the crystal phases was made using the International Center for Diffraction Data(ICDD) diffraction database.13 Morphologic characterization was performed byscanning electron microscopy (SEM) (JEOL, Model JSM –6301F) operated at 25 kV. Samples were coated with gold.Chapter Eleven 205Results and DiscussionThe diffractograms presented on Fig. 1 show that the orthorhombic structure of the PbO (ICDD: 38-1477) was not changed upon the heat treatments, and in accordance no colour change was observed.             A15 30 45 60 752 /ºA4AA1A2A3A4Figure 1 – X-ray diffraction patterns of sample A (PbO from Merck – yellow) and samples obtained after sucessive calcinations. ( - PbO orthorhombic: ICDD 38-1477).The results obtained with sample B (Fig. 2) show the importance of the crystal structure of the precursor to obtain accomplish phase transformations. Infact, although sample B has the same chemical composition of sample A, that is, both are PbO, structurally they are different. Sample A is a pure orthorhombicphase, but sample B has some fraction of base centred orthorhombic structure(ICDD: 35-1482) which allowed that after the third heating the presence of lead oxide (Pb3O4: ICDD 8-19) was denoted by the appearance of diffraction peaks at 26.5, 30.9 and 34.1 º 2 . The evolution observed was reflected on the change of colour since after the four heating the initial light orange coloration changed to more dark orange.The results obtained using sample C, a mixture of orthorhombic and base centred orthorhombic phases, are displayed in Fig. 3. On the contrary of what is observed for sample B, in this case the predominant phase is the base centred orthorhombic. This difference seems to be important to promote the structural evolution upon heat treatments, since in this case the presence of lead oxide started to be observed after the first calcination, as pointed out by the small diffraction peak at 26.5 º 2 . The sample obtained after the forth heating (C4) isalso structurally different from sample B4 since a larger fraction of Pb3O4 isobserved. In what concerns the colour evolution there was no significant Chapter Eleven 206alteration since, among all the starting compounds, sample C was the onepresenting the more intense orange coloration. B15 30 45 60 752 /ºB4BB1B2Figure 2 – X-ray diffraction patterns of sample B (PbO from Merck – orange) and samples obtained after sucessive calcinations. (  - PbO orthorhombic: ICDD 38-1477; - PbO base centred orthorhombic: ICDD 35-1482;  - Pb3O4: ICDD 8-19). C15 30 45 60 752 /ºC4CC2C3C4Figure 3 – X-ray diffraction patterns of sample C (PbO from M&B – orange) and samples obtained after sucessive calcinations. (  - PbO orthorhombic: ICDD 38-1477; - PbO base centred orthorhombic: ICDD 35-1482;  - Pb3O4: ICDD 8-19).The last lead oxide essayed was sample D which is chemically differentfrom all the previous compounds, since it is a Pb (IV) compound while theothers are Pb(II) oxides. Structurally sample D is a mixture of crystalline phases: tetragonal and orthorhombic. The X-ray powder diffraction patterns of the samples obtained after the successive heatings (Fig. 4) show that structuralChapter Eleven 207changes started from the first calcinations, but the more significant change onlyoccurs when the temperature was increased to 450 ºC in the third treatment. In fact, after this treatment Pb3O4 is the major phase present and after the forth treatment is even the only phase detected. These significant structural transformations were reflected in the colour of the samples that changed from black to orange.              D15 30 45 60 752 /ºD4DD1D2Figure 4 – X-ray diffraction patterns of sample D (PbO2 from M&B – black) and samples obtained after sucessive calcinations. ( - PbO2 orthorhombic: ICDD 41-1492; - PbO2tetragonal: ICDD 37-517;  - Pb3O4: ICDD 8-19). The preparation of red lead from lead basic carbonate was made from sample E and from the white lead pigment commercialized by Kremer Pigment.The diffractograms presented in Fig. 5 correspond to the samples obtained after the 4-step experimental procedure. For comparison, the X-ray powder diffraction patterns of commercial Pb3O4 is also presented in Fig. 4. Acording to the diffractograms, lead oxide Pb3O4 is the only phase in the material obtained from 2PbCO3·Pb(OH)2, .while white lead from Kremer Pigment (a mixture of cerussite, PbCO3, and hidrocerussite, Pb3(CO3)2(OH)2) originates a material thatreveals diffraction lines of cerussite at around 30, 32, 34 and 48 º 2 , besides those of the red lead phase. The presence of cerussite results in a lowcrystallinity of the obtained material.  The SEM images of samples more structurally alike Pb3O4 are presented in Fig. 6. Concerning the grain distribution, it is evident that C4 is the moreheterogeneous sample. This finding is in accordance with the previous discussion, since the starting PbO is clearly presented in the XRD pattern of sample C4. Among the others three samples, D4 has the greater homogeneity.The transformation of sample E and white lead from Kremer Pigmente resulted in materials with an intermediate heterogeneity. For these two last samples, noChapter Eleven 208correlation between the structural results and the morphologic analysis were detected.15 30 45 602 /º(i)(ii)(iii)Figure 5 – X-ray diffraction patterns of (i) Pb3O4 and samples obtained after heattreatments of (ii) 2PbCO3·Pb(OH)2 and (iii) white lead pigment from Kremer Pigment. (ii)(i)(iv)(iii)Figure 6 – SEM images of the samples obtained after heat treatments of (i) PbO from M&B – orange; (ii) PbO2 from M&B – black; (iii) 2PbCO3·Pb(OH)2 and (iv) white lead pigment from Kremer Pigment.Chapter Eleven 209ConclusionsThe results obtained in the present study point out the importance of thestarting compound for the preparation of red lead. Actually pure lead oxidephase was obtained only for the transformation of PbO2 and 2PbCO3·Pb(OH) 2.The presence of red lead phase was also observed for PbO starting materials presenting a mixture of structural phases. When the use of white lead KremerPigment was considered, red lead was the main crystal phase present, althoughthe lead carbonate phase remains present, what is reflected in the crystallinity of the sample.Acknowledgments This work was supported by Fundação para a Ciência e Tecnologia(Portugal) through project POCI/EAT/58065/2004. Chapter Eleven 210Notes1 P. Ball, Bright Earth. Art and the Invention of Color (Chicago, 2001); António J. Cruz, As Cores dos Artistas. História e Ciência dos Pigmentos Utilizados em Pintura (Lisboa, 2004); F. Delamare, B. Guineau, Colour. Making and Using Dyes and Pigments(London: Thames and Hudson, 2000); A. Varichon, Colors. What they mean and how to make them (New York, 2006).2 E. West FitzHugh, Red Lead and Minium, in Artists' Pigments. A handbook of their history and characteristics Vol. 1, ed. R. L. Feller (Washington, 1986).3 Cruz, As Cores dos Artistas; FitzHugh, Red Lead and Minium.4 Filipe Nunes, Arte Poetica, e da Pintura, e Symmetria, com Princípios da Perspectiva(Lisboa: Pedro Crasbeeck, 1615). 5 Although in the English translation presented here, done by Veliz, it is said “Others usewhite lead in place of lead sheets”, Nunes, in the original Portuguese text, said “Outros em lugar de enxofre põem Alvayade” [Nunes, 1615, p. 66v], that is, what it is replacedby white lead it is not the lead sheets but the sulphur. Therefore, we corrected the Veliz’stranslation.6 Zahira Veliz, Artists' Techniques in Golden Age Spain. Six Treatises in Translation(Cambridge, 1986).7 C. S. Smith, J. G. Hawthorne, “Mappae Clavicula. A litlle key to the world of medievaltechniques”, Transactions of the American Philosophical Society 64 (4) (1974), 3-128.8 Theophilus, On Divers Arts. The Foremost Medieval Treatise on Painting, Glassmaking and Metalwork, ed. J. G. Hawthorne and C. S. Smith (New York, 1979). 9 M. P. Merrifield (ed.), Medieval and Renaissance Treatises on the Arts of Painting(New York, 1999).10 Merrifield, Medieval and Renaissance Treatises11 E. M. Otto, “Equilibrium pressures of oxygen over oxides of lead at various temperatures”, Journal of the Electrochemical Society 113 (6) (1966), 525-527; G. L. Clark, N. C. Schieltz, T. T. Quirke, “A new study of the preparation and properties of thehigher oxides of lead”, Journal of the American Chemical Society 59 (11) (1937), 2305-2308; G. L. Clark ,W. P. Tyler, “Studies on lead oxides.II. Hydrous, normal and activelead monoxides”, Journal of the American Chemical Society 61 (1) (1939) 58-65; G. L.Clark, R. Rowan, “Studies on lead oxides.IV. Polymorphic transitions by grinding, distortion and catalytic activity in PbO”, Journal of the American Chemical Society 63 (5) (1941), 1302-1305; G. L. Clark, R. Rowan, “Studies on lead oxides.V. Further experiments on compounds of the type PbOn(n = 1 to 2)”, Journal of the American Chemical Society 63 (5) (1941), 1305-1310; K. Gavrichev, A. Bolshakov, D. Kondakov, S. Denisov, Thermal Transfornmations of Lead OxidesJournal of Thermal Analysis and Calorimetry 92 (3) (2008), 857-863. 12 Clark, Rowan, (1941) 1302-1305; Clark, Rowan, (1941) 1305-1310.13 International Center for Diffraction Data, Power Diffraction File Alphabetical Index(PA, 1988).

Theory vs practice: synthesis of red lead following ancient recipes

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Theory vs practice: synthesis of red lead following ancient recipes

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