Some Occurrences of Patent Yellow

Some Occurrences of Patent Yellow

Some Occurrences of Patent Yellow

Svetlana Pisareva

Patent yellow (lead oxychloride, PbCl2 .5-7PbO) has been identified by microscopic, chemical and powder X-ray diffraction analysis of samples from several paintings from the seventeenth to the nineteenth centuries. The presence of this pigment in seventeenth-century paintings confirms its use before it was reported by Schcele in 1770 and a method for its production patented in the 1780s. Rather, patent yellow seems to have been in use for several centuries, but employed less frequently than other lead-containing pigments such as lead-tin yellow and Naples yellow.

INTRODUCTION

Sometimes, while studying paintings, a pigment occurs that is similar in appearance to lead-tin yellow, but which elemental analysis indicates contains lead but no tin. X-ray microspectrometry shows that lead and chlorine are the major elements present. This pigment, lead oxychloride (PbCl2 .6PbO), has several synonyms, ncluding patent yellow, Kassler yellow, Turner's yellow, mineral yellow and Veronese yellow.

In 1979, an article by White in the American Mineralogist reported that lead oxychloride had first been mentioned in the scientific literature in 1916 [1]. The collection of the American National Museum of Natural History contains a sample of the mineral lorettoite, named after the town in the state of Tennessee from which the sample came to the museum. However, having researched this museum sample, White came to the conclusion that it is an artificial, man-made material [1|.

White's article also refers to Harley's book on seventeenth- to nineteenth-century artists' pigments [2].

Harley discusses the pigment called patent yellow (PbCl2 .5-7PbO), which she describes as being discovered by Scheele in 1770 as a by-product of soda production, some years before his discovery of a new-green pigment known as Scheele's green. The method of manufacture was patented in England by James Turner in 1781 as 'a method of producing a yellow colour for painting in oil or water. . .' [2], The method of manufacture required a lead oxide, either minium (Pb3O4) or litharge (PbO), to be ground with half the weight of sea salt in solution. After the mixture had been allowed to stand for 24 hours, the caustic soda that had been produced was poured off and the white residue calcined until the colour changed to yellow.

METHODS OF ANALYSIS

Polarizing microscopy

Under the polarizing microscope the differences in particle morphology between patent yellow and other yellow lead-containing pigment particles (lead-tin yellow and Naples yellow) can be seen. Patent yellow

crystals are transparent in transmitted polarized light and show a pale-yellow colour, unlike lead-tin yellow and Naples yellow particles, which appear as clusters of micro-particles. Under crossed nicols the centres of patent yellow particles appear dark, which is not typical for other lead-containing yellow pigments.

Microchemical tests

Positive reactions for the presence of chloride ions (using silver nitrate reagent, AgNO3) and lead ions (with potassium iodide, KI) can help to ascertain the presence of the pigment without the need for instrumental techniques. Despite this, an identification using X-ray diffractometry should be considered the most reliable method.

X-ray microspectrometry

Energy dispersive X-ray spectrometry in the scanning electron microscope (SEM-EDX) will serve to identify the presence of both lead and chlorine. Again, the exact nature of the lead/chlorine compound present cannot be determined by this method.

X-ray powder diffractometry

If sufficient sample is available, lead- and chlorine-containing samples suspected to be patent yellow can be identified by comparison of their X-ray powder diffraction pattern with that for lead oxychloride (Pb7O6Cl2) [3]. For convenience, the data from the relevant ICDD file (PDF 6-393) are reproduced in Table 1.

HISTORY OF USE

In the opinion of Harley, the pigment was obtained for the first time in the eighteenth century and used widely during the first half of the nineteenth century before being largely superceded by chrome yellow. However, patent yellow was still produced in quantities in the nineteenth century, in spite of the introduction of new yellow pigments. In the middle of the century it was being produced at Washington (in County Durham, UK) by the Washington Chemical Company, who demonstrated paint samples and examples of their application in oil painting at the Great Exhibition in London in 1851.

There is, however, an alternative view of the history of the use of lead oxychloride. In the section on yellow pigments in his book on painting materials, Kühn refers to a pigment that was known by several names –

Table 1 X-ray powder diffraction data for patent yellow (ICDD PDF 6-393)

Figure 1 Gerard de Lairesse (1641-1711), 'Wedding of the Gods', oil on canvas. Private collection.

Figure2 A.F. Charper (1725-1806), 'Gate in Cliffs'. 1786, oil on canvas. Museum of the Stroganov Higher Industrial Arts School.

Kasslergelb, Turnergelb, Mineralgelb, Veronesergelb and Patentgelb [4]. These have the same composition as the patent yellow described by Harley, that is,

Table 2 Occurrences of patent yellow

chem = microchemical tests

micr = light microscopy, polarizing microscope

SEM-EDX = scanning electron microscopy with energy-dispersive spectroscopy (microscope JSM 5300, LINK ISIS)

XRD = X-ray powder diffraction analysis using a Debye-Scherrer camera

Figure 3 Russian school, nineteenth century, 'St Jerome in his cell', oil on cardboard mounted on canvas. State History Museum, Moscow.

PbCl2 .6PbO. It is Kiihn's opinion that this pigment had been known for centuries, but was applied less frequently than lead-tin yellow and Naples yellow.

OCCURRENCES

During our examination of easel paintings, this pigment has been found in seven paintings. Four of these paintings are Dutch and date from the seventeenth century, two are from eighteenth-century Germany, and the last is a nineteenth-century Russian work. In addition, lead oxychloride was identified by M.M. Naumova in a nineteenth-century Russian icon [5]. Details of some of these occurrences and the analytical methods used are given in Table 2.

These findings lead to the conclusion that lead oxychloride (patent yellow) was used in the seventeenth, eighteenth and nineteenth centuries. The question of when it was first used in paintings remains open, but it was certainly before its 'discovery' by Scheele and the issue of a patent to Turner. It is also as yet unknown whether its production continued in the twentieth century, as was the case for Naples yellow, which, although known since the sixteenth century, has been identified in paintings executed at least as late as the second decade of the twentieth century.

ACKNOWLEDGEMENTS

The work on identification of yellow lead oxychloride was developed in collaboration with A.V. Mokhov and O.W. Karimova from the Institute of Geology ot Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences (IGEM RAS).

REFERENCES

1 White, J.S., 'Lorettoite discredited and chubutite reviewed', American Mineralogist 64 (1979) 1303-1305.

2 Harley, R.D., Artists' Pigments c. 1600-1835, 2nd revised edn, Archetype, London (2001) 99-100.

3 ICDD, International Centre for Diffraction Data, PDF 6-393.

4 Kiihn, H., 'Farbmaterialien. Pigmente und Bindemittel', in Rcdams Handbuch der kiinstlerischen Technikcn, Band 1, Philipp Reclamjun., Stuttgart (1984) 28.

5 Pisareva, S., 'Chronology of pigments', supplement to From Fayum Portraits to Post

Impressionism: The Histor)' of Technology of Easel Painting, ed. |. Grenberg, Moscow (2004) 255.

AUTHOR

SVETLANA PlSAREVA obtained a doctorate from the Moscow Institute of Chemical Engineering. She is now on the staff at the State Research Institute for Restora-

tion (GNIIR) where she is engaged in the study of wall and easel painting techniques.

Address: GNIIR, 44 Gastetto St., Moscow 107014, Russia. Email: gosniir@mail.cnt.ru

Résumé — Le jaune « Patent »* (oxychlorure de plomb, PbCl;5-7PbO) a été identifié par microscopie, tests chimiques et diffraction des rayons X dans des échantillons provenant de plusieurs tableaux datant du XVIIe au XIX siècle. La présence de ce pigment dans des peintures du XVII siècle confirme sou usage avant qu'il soit rapporté par Scheele en 1770 et sa méthode de fabrication brevetée dans les années 1780. En fait, le jaune « Patent « semble avoir été utilisé depuis plusieurs siècles, mais employé moins fréquemment que d'autres pigments à base de plomb tels que le jaune de plomb et d'étain et le jaune de Naples.

* eu français, jaune de Cassel, ¡aune de Paris, jaune de Turner; ndt.

Zusammenfassung — Patentgelb (Kasslergelb, Blcioxichlorid, PbCI;5-7PbO) konnte mit Hilfe der Mikroskopie, der Mikrochemie und der Röutgcnpulverdiffraktomctrie auf verschiedenen Gemälden des 17. bis 19. Jahrhunderts nachgewiesen werden. Der Nachweis des Pigmentes in Gemälden des 17. Jahrhunderts bestätigt, dass Patentgelb noch vor der ersten Publikation durch Scheele und der Patentierung der Produktionsweise Verwendung fand. Patentgelb scheint schon einige Jahrhunderte vorher benutzt worden zu sein, wenn auch weit seltener als andere bleihaltige Pigmente wie Bleizinngelb oder Neapelgelb.

Resumen — El llamado "amarillo patente" (oxicloruro de plomo, PbCI;5-7PbO) ha sido identificado por medio de microscopía, por procedimientos químicos y por difracción de rayos X del polvo a partir de varías muestras desde el siglo XVII al XIX. La presencia de este pigmento en pinturas del siglo XVII confirma su uso anterior a la mención que de él hace Scheele en 1770, asi como de un método de producción patentado en la década de los ochenta de esc mismo siglo. Más bien parece ser que este amarillo ya había sido utilizado durante varios siglos, aunque empleado de una manera más limitada que otros pigmentos basados en el plomo como el amarillo de plomo y estaño y el amarillo de Ñapóles.