Lead Tin Yellow Type Research Articles

Ceramic floor tiles with yellow pigment from Kievan Rus’: A technological study

Colored glazed ceramic tiles were widely used for paving floors of the main buildings, mostly Orthodox churches, in the Kievan Rus’ (10th-13th centuries AD). The production of ceramic floor tiles was localized near the site of construction, and the date of production can be attributed to the date of construction or renovation of the church. Therefore, the study of glazed tiles makes it possible to determine the local and chronological features of their production technology.. Local production technology in Ancient Rus' was studied using thirteen yellow glazed ceramic tiles from six cities (Kiev, Galich, Polotsk, Vladimir-Volynsky, Pereslavl-Zalessky and Novgorod). Also, two samples were selected from churches in Polotsk, Vladimir-Volynsky and Vyshgorod at different times of construction or renovation to study chronological variations in tile production technology. Chemical compositions and crystalline phases of yellow glaze and ceramic body have been analyzed by X-ray diffraction, Raman and X-ray fluorescence spectroscopy. In all cases, samples of ceramic tiles were glazed with high-lead silicate glass, and lead tin yellow type II (PbSn1-xSixO3) was used as a pigment. Local production technology in Ancient Rus' was studied using thirteen yellow glazed ceramic tiles from six cities (Kiev, Galich, Polotsk, Vladimir-Volynsky, Pereslavl-Zalessky and Novgorod). Also, two samples were selected from churches in Polotsk, Vladimir-Volynsky and Vyshgorod at different times of construction or renovation to study chronological variations in tile production technology. Most likely, the glaze layer on the ceramic tile was formed using pre-synthesized glass; this technology differs from the conventional technology for pottery, uses lead oxide or a mixture of lead oxide and quartz. Data on the chemical composition of yellow lead glazed tiles dating from the 10th-13th centuries AD can be used to determine the region of glazed ceramic production.

Glass-based pigments in painting: smalt blue and lead\u2013tin yellow type II

Glass-based pigments have an important role in the panorama of artistic production due to the fact that their manufacturing processes involve a combination of different skills and understanding, and they have a role in disciplines ranging from glass technology to metallurgy, from glazed ceramic to stone imitation and from vitreous mosaic tesserae to painting materials. The main goal of this manuscript is to present a critical review of the literature relating to blue smalt and “yellow glass” (lead–tin yellow type II) pigments: presenting their historical background, the analytical protocol, the processes of alteration and decay and finally tracing issues. Several case studies analyzed by the authors will be presented. Particular attention was devoted to the correlation between micro-textural features and decay processes affecting the studied pigments, though the widespread heterogeneity of the analyzed materials and the variability of the artistic techniques in which the pigments were used as well as the effect of the relevant (micro-)environmental conditions dictate a cautious approach. These studies are presented in the context of information about the chain of production, the selection of the raw materials and relevant provenance studies.

Characterization of glass beads from Nanhai I shipwreck and new evidence of lead tin yellow type II in China

Glass beads excavated from Nanhai I shipwreck were investigated with scanning electron microscopy with energy dispersive spectrometer (SEM–EDS), Raman spectroscopy, multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and X-ray diffraction (XRD). Dating back to the Southern Song Dynasty, these beads help to study Chinese maritime trades during the twelfth–thirteenth century. The bead samples are categorized into five groups by color, i.e., yellow, orange-red, blue, dark red and light red. All beads are of K2O-PbO-SiO2 and PbO-SiO2 glass systems and in form of coil bead, which further confirms the Chinese origin of them. Lead tin yellow type II was identified in the opaque yellow coil beads, and K2SnxPb(1-x)Si3O9 crystals were found in both yellow and orange-red samples. Through the preparation of glass with the same formula as the ancient yellow beads, lead tin yellow type II was probably synthesized beforehand and added as colorant because its raw materials tend to form K2SnxPb(1-x)Si3O9 crystals in the K2O-PbO-SiO2 glass during firing. As lead tin yellow type II is an atypical colorant in China, these beads from Nanhai I shipwreck may serve as the first clear evidence of lead tin yellow type II presenting in the Chinese glass system. The lead isotope ratios of the yellow beads suggest they were produced in Fujian Province, China. The introduction of the lead tin yellow coloring technique might have a close connection to the glass making in the Southeast Asia and these beads seemed to be made specifically for overseas markets.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Raman and X‐ray fluorescence glaze characterisation of Maria Keil's decorative tile panels

AbstractA set of decorative contemporary tile panels, created by the Portuguese artist Maria Keil (1914–2012) for the Lisbon metro stations, was studied under a noninvasive analytical methodology. This methodology combines X‐ray fluorescence spectrometry (μ‐XRF) and Raman spectroscopy in microscopic (μ‐Raman) mode for an elemental and structural composition characterisation of the glaze (glass matrix and network modifiers such as fluxes, opacifiers and colouring agents). μ‐XRF quantitative evaluation of the glassy matrix shows that all glazes have a lead silicate glass base. Results obtained by the combined use of μ‐XRF and μ‐Raman show that a zirconium‐based opacifier was used. Naples yellow (Pb2Sb2O7), lead–tin yellow type II (Pb(Sn,Si)O3), Pb–Sn–Sb triple oxide, cobalt blue (CoAl2O4), chromium oxide (Cr2O3) and malayite sphene (CaO·SnO2·SiO2) have been identified by μ‐Raman as some of the colouring agents, either used by themselves or in mixtures for obtaining the desirable colours intended by the artist.

Polychrome sculptures of medieval Italian monuments: Study of the binding media and pigments

The Ferrara cathedral and Parma baptistery are exceptional medieval monuments and results of a technical study of the polychrome sculptures and reliefs are presented here. The results are an extension of past diagnostic projects carried out between the 1970s and 90s, and support the re-examination of previous investigations. Scientific and historical accounts describe medieval sculpted portals of European cathedrals as a prime example of the diffusion of the polychrome painting techniques. The technical study of paint fragments of ancient polichromy is complex and requires sophisticated instrumentation to inform colour reconstructions. In this study, micro-Raman classified pigments and gas chromatography mass spectrometry (GC/MS) identified the organic binding media on the pre-treated stone, primers, painted layers, and gilding. GC/MS analysis of samples from the Ferrara cathedral detected fatty acids that most closely match linseed oil and dehydroabeitic acid, a marker for pine resin, which was detected for the first time in the primer from the Ferrara cathedral panels. The Parma baptistery samples contained amino acids indicating the presence of protein and oil. Raman analysis added novel results on the pigments used, such as lead-tin yellow type I and orpiment, as well as on the state of conservation of paint layers. The data were also compared to a wide range of publications and were found to significantly contribute to the knowledge and research in architectural polychromy in the Romanesque–Gothic era.

A unique recipe for glass beads at Iron Age Sardis

In large parts of the Mediterranean recipes for the earliest man-made glass changed from melting mixtures of crushed quartz pebbles and halophytic plant ashes in the Late Bronze Age to the use of quartz sands and mineral soda during the Early Iron Age. Not much is known about this transition and the experimental materials which would inevitably have been connected to such technological change. In this paper we present a unique snapshot of developments in glass technology in Anatolia during the Middle Iron Age, when glass is still a relatively rare commodity. The present work focusses on black glass beads decorated with yellow trails from eighth to seventh century BCE Sardis, glass beads that are very rare for this period, and on this site. A full elemental analysis of the beads was made, and Sr, Pb and B isotope ratios were determined. This study reveals the use of a combination of a previously unknown source of silica and of mineral soda, giving rise to elevated (granite-like) Sr isotope signatures, as well as high alumina and B concentrations. The yellow trails of glass on the beads consist of lead-tin yellow type II, lead stannate, showing the earliest occurrence of this type of opacifier/colourant so far, predating any other findings by at least four centuries. The production of these glass beads may be local to Sardis and experimental in nature. It is therefore suggested that Sardis may have played its role in the technological development of the glass craft during the Iron Age.

A Raman microspectroscopy-based comparison of pigments applied in two gothic wall paintings in Slovenia

The present study deals with the characterisation of pigments used in two overlaid gothic wall paintings from the former 13 th century Minorite church of St. Francis of Assisi (Koper, Slovenia), in order to define differences in the technologies used. Paint layer samples were analysed via Raman microspectroscopy, supported by SEM/EDS and FT-IR analysis, when necessary. The results revealed that the 14 th century mural was painted mainly a fresco with final elements a secco, a technique typical of Italian mediaeval wall painting. In contrast, the 15 th century painting was executed mostly a secco , a technique often applied in Northern Europe and the Alpine region. The differences between the two paintings are especially obvious in the pigments applied. While the earlier painting is characterised by azurite, carbon black, red and yellow ochres, lime white and green earth, the palette used for the younger painting is much broader. In addition to red and yellow ochres, carbon black and lime white, lead pigments such as lead white, red lead and lead-tin yellow type I were also determined, as well as a number of expensive pigments including cinnabar, azurite and malachite. Also found in the younger painting was the rare orange yellow pigment vanadinite. In both layers, azurite was applied a secco for the background area. Gilding was confirmed in both layers, carried out as application of gold leaves on red bole (in the earlier mural) and on mordant (on a younger, superimposed (overlaid painting), which is quite exclusive and rare for Slovene mediaeval painting. In the younger layer also a use of tin foil for secondary elements was discovered.

Saponification in egg yolk-based tempera paintings with lead-tin yellow type I

Saponification occurring in paint layers of artworks represents a serious degradation process affecting the appearance and stability of paintings. Formation of metal soaps is mostly reported as a consequence of the interaction of lead white or zinc white with oil binder. We found the distinct symptoms of saponification in paint layers consisting of lead-tin yellow type I and egg yolk binder in a panel painting from the 15th century. This scarce finding induced the study of interactions between lead-tin yellow type I with three different binders: (i) egg yolk tempera, (ii) emulsion of egg yolk and oil, and (iii) oil. The interactions were studied in long-term model experiments using infrared spectroscopy (FTIR) and powder X-ray diffraction (XRD). Based on the results, a set of mixed lead carboxylates of the series Pb(C16)2-x(C18)x, where x = 0; 0.25; 0.5; 0,75; 1; 1.5 and 2, was synthesised as reference materials suitable as a basis for proper identification of neo-formed lead soaps by FTIR and XRD. The formation of lead soaps was detected already within 1 month of reaction in egg yolk containing binders, whereas no soap was formed during 6 months of the experiment in the oil mixture. The neo-formed soaps are various mixed lead carboxylates containing both palmitate (C16) and stearate (C18) in one crystal structure and the proportion of carboxylate anions is affected by the type of the binder. We found the C16:C18 ratio in mixed lead carboxylates is higher in egg yolk tempera samples in accordance with the more abundant palmitic acid in egg yolk fat. On the other hand, the lower C16:C18 ratio in emulsion binder correlates with increased content of stearic acid, suggesting contribution of both binders, i.e. egg yolk and oil, to the soap formation.

Development of a new portable X-ray powder diffractometer and its demonstration to on-site analysis of two selected old master paintings from the Rijksmuseum

A portable X-ray powder diffractometer (p-XRD) PT-APXRD III has been developed for on-site analysis of paintings and archaeological samples. By using a Cu anode X-ray tube and a silicon drift diode (SDD) detector, diffraction patterns with a high signal-noise (S/N) ratio can be recorded. The X-ray tube can be operated at a maximum voltage of 60kV, which makes it possible to simultaneously record X-ray fluorescence spectra up to the high-energy region. The total weight of this instrument is 16kg, which can be carried anywhere and the goniometer unit (5.6kg) can be placed on a tripod for analysis of mural paintings. We brought the instrument to the Rijksmuseum in the Netherlands to examine its applicability for the analysis of oil paintings. We successfully analyzed two seventeenth-century oil paintings by Johannes Vermeer and Jan Davidsz de Heem (copy after). Ultramarine blue, lead-tin yellow type I, and Naples yellow were identified from the diffraction patterns, demonstrating the high practicality of this instrument. Furthermore, it was found from the SEM-EDX analysis of a paint cross section that the yellow pigment was applied in separate layers rather than being mixed. This diffractometer will be commercially available in the near future and will have many applications in the field of material analysis.

Unusual pigments found in a painting by Giotto (c. 1266-1337) reveal diversity of materials used by medieval artists

The important trecento Florentine artist Giotto (c. 1266-1337) is renowned for his naturalistic and realistic works in tempera and fresco. His innovative paintng style involved painting expressive, emotive faces and use of pictorial devices for depicting space. This report focuses on the analysis of the materials and methods used in a panel in the collection of the National Gallery of Art, Madonna and Child (1310/1315). Giotto used inky washes under thin layers of egg tempera paint. Yellow iron earth and lead tin yellow are present in the paint used to depict the lining of the Virgin’s mantle. SEM-EDX of one of the yellow pigments confirmed it is lead tin yellow type II, PbSn1-xSixO3. The ratio of colorant to the glassy phase indicates this material was produced for use as a pigment rather than as a glass. Ultramarine was not used in this painting, azurite is the blue pigment. The azurite used here does not contain elemental impurities, however malachite and the rare green–blue mineral mixite, BiCu6(OH)6(AsO4)3(H2O)3, are found in the blue paint. We do not know if Giotto intentionally used mixite as a green–blue pigment or if it was adventitious with the azurite, though given the rarity of the mineral, the latter is more probabale. Nevertheless, the artist’s choice of color was deliberate and the presence of mixite and the clear-hued lead tin yellow pigment attest to his coloristic decisions, in this case opting for cool hues rather than the warm blue of ultramarine which we typically associate with paintings of the Madonna from this time period.

An investigation of the lead tin yellows type I and II and their use in Bohemian panel paintings from the Gothic period

AbstractBackgroundPresented article summarizes the results of a broad-based survey on painting techniques used during the High and Late Gothic period in the Bohemian panel paintings located in the collections of the National Gallery in Prague. The work is focused on the specific use of yellow pigments – lead tin yellow type I and type II in the panel painting from the period around 1340–1550. In the scientific investigation supplementary microscopic and spectral analyses were made. A representative range of 57 micro-samples collected from the 36 panel paintings of the 21 Masters and their workshops was investigated by the methods of optical microscopy on polarizing microscope (OM). Molecular analysis of both types of yellow was performed using Raman micro-spectroscopy (RMS). The use of this technique was crucial for the nondestructive differentiation between each type of lead-tin yellow.ResultsThanks to the Raman spectroscopy it was possible for the first time to map the usage of lead tin yellow type I and II in such a broad range. Combination of the analytical techniques brought the knowledge about the morphology of the grains and variability of the use of the lead tin yellows in the Bohemian panel paintings.ConclusionsThe contribution offers a systematic view on the outcomes and in a synoptic way consults the results of respective scientific methods. It clearly confirms both the temporally and locally specific use of both types of lead tin yellows. The presented facts are the results of interdisciplinary collaboration among the scientists and the art historian.

Raman microspectroscopic analysis of pigments of the Gothic wall painting from the Dominican Monastery in Ptuj (Slovenia)

The study deals with the characterization of pigments from the newly discovered wall painting at the Dominican Monastery in Ptuj (Slovenia) in order to acquire detailed information about the technology used, as well as to identify the deterioration products. The uncovered wall painting, depicting a vivid procession of riders, is dated to the late 14th century. Painting techniques and pigments were analysed by optical microscopy and Raman microspectroscopy. The optical microscope revealed that the wall painting was executed in a lime technique characteristic of the Central‐European artistic expression. Several natural and synthetic inorganic pigments, such as azurite, red and yellow ochres, cinnabar, red lead, lead white, lime white, lead–tin yellow type I and carbon black were identified. Surprising identification of the type I of lead–tin yellow used already in the 14th century is of high importance, since, until now, it was considered that it appeared on the market only in the first half of the 15th century. Plattnerite was observed as a result of degradation of lead pigments. The use of expensive azurite and cinnabar could indicate a wealthy client. Copyright © 2014 John Wiley & Sons, Ltd.

207Pb and 119Sn solid-state NMR and relativistic density functional theory studies of the historic pigment lead-tin yellow type I and its reactivity in oil paintings.

Lead soaps (lead carboxylates) have been detected in traditional oil paintings in layers containing the pigment lead-tin yellow type I (LTY-I). LTY-I has been used by artists from at least the second quarter of the 15th century until the first half of the 18th century. Soap formation can lead to protrusions in paint layers and increased transparency, causing the paint support to become visible. We have characterized LTY-I by (119)Sn and (207)Pb solid-state NMR (ssNMR) spectroscopy. Using a combination of NMR techniques and DFT molecular cluster calculations, we identify the individual species in LTY-I and determine their (119)Sn and (207)Pb chemical-shift tensors. The presence of starting materials from the synthesis, minium, and tin(IV) oxide was also verified. Knowledge of the chemical-shift tensor components and the impurities in LTY-I is important for examining the chemistry of degradation processes and soap formation. We demonstrate that ssNMR can be used to detect reaction between Pb2SnO4 and added palmitic acid in a model paint sample containing LTY-I.

Analysis of Lead Carboxylates and Lead-Containing Pigments in Oil Paintings by Solid- State Nuclear Magnetic Resonance

ABSTRACTSoap formation in traditional oil paintings occurs when heavy-metal-containing pigments, such as lead white, 2Pb(CO3)2·Pb(OH)2, and lead-tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 μm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. In addition, soap formation has been reported to play a role in the increased transparency of paint films that allows the painting support, the preparatory drawing, and the artists’ alterations to become visible to the naked eye. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood. To elucidate these issues, chemical and structural information is necessary which can be obtained by solid-state 207Pb, 119Sn, and 13C nuclear magnetic resonance (NMR). In the present study, a combination of 207Pb NMR pulse sequences was used to determine accurately the NMR parameters of lead-containing pigments and lead carboxylates known to be involved in soap formation, such as lead palmitate, lead stearate, and lead azelate. These results show that the local coordination environment of lead azelate is different from lead palmitate or lead stearate and therefore it is unlikely that lead azelate would be incorporated into an ordered structure containing lead palmitate and lead stearate. In addition, the chemical shifts of the pigments obtained are different from those of the soaps, demonstrating that 207Pb NMR is useful in characterizing the components when present in a mixture, such as a paint film. The NMR methods discussed can also be applied to other Pb-containing cultural heritage materials, electronic and optoelectronic materials, superconducting materials, and environmentally contaminated materials.

Pigment identification of an illuminated mediaeval manuscriptDe Civitate Deiby means of a portable Raman equipment

Direct identification of pigments in mediaeval illuminated manuscripts was one of the first applications of Raman spectroscopy in art and archaeology. In previousin situanalysis of handwritings, the equipment was typically provided with a single excitation source. In this work, a portable Raman spectrometer (EZRAMAN‐I‐DUAL Raman system) is introduced to characterise the pigments used in an important illuminated mediaeval manuscript,De Civitate Dei(Library in Bruges, Ms.106). Characteristics important for thesein situmeasurements were discussed. We introduce a set‐up that allows stable positioning of the equipment and point out the advantage of the availability of two lasers, which are part of the instrument. Good performance of the introduced Raman spectrometer, to allow pigment identification in a short time, is proved. Finally, pigments such as lead white (2PbCO3 · Pb(OH)2), lead–tin yellow type I (Pb2SnO4), malachite (Cu2CO3(OH)2), mosaic gold (SnS2), vermillion (HgS), carbon black (C), red lead (Pb3O4) and azurite (Cu3(CO3)2(OH)2) could be identified. These pigments were often used in mediaeval artworks and contribute to the enrichment of information of the materials used by the illuminator. Copyright © 2014 John Wiley & Sons, Ltd.

Nuclear Magnetic Resonance Spectra and 207Pb Chemical-Shift Tensors of Lead Carboxylates Relevant to Soap Formation in Oil Paintings

Soap formation in traditional oil paintings occurs when heavy-metal-containing pigments, such as lead white, 2PbCO3·Pb(OH)2, and lead tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 μm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood. To elucidate these issues, chemical and structural information is necessary, which can be obtained using solid-state (207)Pb and (13)C nuclear magnetic resonance (NMR). In this article, we report (207)Pb and (13)C solid-state NMR spectra and (207)Pb chemical-shift tensors of lead carboxylates implicated in soap formation: lead stearate, lead palmitate, and lead azelate, in addition to lead oleate and lead heptanoate for comparison. The (13)C cross polarization with magic-angle spinning (MAS) spectra of these lead carboxylates show resonance doubling for the carbons closest to the lead, indicating two different conformations of the fatty acid chains in the asymmetric unit. The (207)Pb NMR spectra, from which tensors were determined, were obtained with direct excitation and spin-temperature alternation, with and without MAS, and with the wide band uniform rate smooth truncation Carr-Purcell-Meiboom-Gill pulse sequence. The results of these experiments show that the local coordination environment of lead azelate is different from lead palmitate and lead stearate and could thus be distinguished from these in a paint film displaying soap formation. In addition, comparing the (207)Pb NMR chemical-shift tensors of the lead carboxylates studied shows that crystal packing of the acyl chains may be a factor in determining the coordination environment around the lead.

Investigation of pigment degradation due to acetic acid vapours: Raman spectroscopic analysis

The preservation of moveable cultural heritage objects inside museums includes trying to keep these objects under the best conditions as possible. This is done, amongst others, by controlling the atmospheric conditions under which the objects are preserved: the amount of light, temperature and relative humidity, etc. should be carefully monitored in exhibitions as well as in storage rooms. However, other atmospheric components may as well be important for the optimal preservation of cultural heritage materials, such as acetic compounds derived from wood package. A study of the degradation of malachite, leadwhite, lead-tin yellow type I, red lead and pigment orange 36 is performed using Raman spectroscopy. The degradation of these pigments was analyzed after exposure to acetic acid vapours. Three different acetic acid concentrations in the atmosphere were tested: ca. 150 ppm, ca. 300 ppm and ca. 500 ppm. In all conditions, the relative humidity was kept constant at ca. 75 %. A possible colour change, which can go hand in hand with the degradation process, was evaluated by observing the change of the RGB values of the sample colour. Besides pigment orange 36, which showed to be unreactive towards the acid atmosphere, acetate species were generated for each pigment: malachite reacted towards a verdigris variety; red lead, leadwhite and lead-tin yellow degraded towards lead acetate. At high doses, red lead alters towards a black pigment, which is presumed to be plattnerite.

A combined spectroscopic study on Chinese porcelain containing ruan-cai colours

Because of its major contributions to the world economy and cultural heritage, Chinese porcelain and its technology can be considered as very important. In this research, the applicability of Raman spectroscopy and X-Ray Fluorescence (XRF) spectroscopy to study the pigments of the ruan-cai colour palette of Chinese porcelain dating from the 18th century was evaluated. Next to the investigations based on stylistic analysis, the use of other analysis techniques is important to obtain complementary information. Raman spectroscopy and XRF spectroscopy are two non-invasive, analytical techniques proven to be useful for the determination of the nature and composition of pigments used to decorate ceramics. As a result, analytical analysis allows us to retrieve more information about the production of Chinese porcelain. Based on visual inspection of the decoration, the objects could be divided into two groups and to evaluate the use of the combined analytical approach, all groups and subgroups were sampled. Before Raman and XRF analyses, the samples were cut, embedded and polished, in order to be able to measure the transversal section of the samples. In this way, each layer of the porcelain samples could be analysed separately. The results show that the blue colour is cobalt-aluminium oxide, in red zones haematite (α-Fe2O3) is present and the green area contains a mixture of CuO in a lead-rich basis and a solid solution of malachite (Cu2CO3(OH)2). The opaque yellow and white colours were identified as lead tin yellow type II (PbSn1−xSixO3, where x ∼ 0.25) and a lead arsenate, respectively.

The Intentional Use of Lead–tin Orange in Indian Islamic Glazes and Its Preliminary Characterization

We describe the historical appearance, composition and texture of a little‐known orange pigment in 17th‐century northern India. The pigment shares similarities with lead–tin yellow type II, but has between 6 and 7 wt% zinc oxide instead of silica as a minor element in its structure, in addition to the dominant lead and tin oxide. The consistency of its occurrence and composition across several important and highly decorated monuments and relatively wide chronological and geographical ranges of use indicate the controlled and intentional production of this pigment. We propose to use the name lead–tin orange for this material, indicating its similarity to lead–tin yellow but highlighting its independent character and distinct colour.