European cobalt sources identified in the production of Chinese famille rose porcelain

Highlights

• European sourced cobalt pigments were used in Qing Chinese Famille Rose porcelain.

• In contrast Chinese sources were used in contemporaneous blue and white underglazes.

• This may reflect a technological choice dictated by the composition of the pigments.

• LA-ICPMS is a powerful tool for determining the pigments and their sources for porcelain.

Abstract

The blue pigments on 112 fragments or small objects of Qing Dynasty Chinese, 95 of underglaze blue and white and 17 overglaze enamelled porcelains were analysed by LA-ICPMS. The underglaze blues on both blue and white and polychrome objects were created with a cobalt pigment that was rich in manganese with lesser nickel and zinc. This suite of accessory elements is generally considered to be characteristic of local, Chinese, sources of pigments. However, the blue enamels were very different. The cobalt pigment here has low levels of manganese and instead is rich in nickel, zinc, arsenic and bismuth. No Chinese source of cobalt with these characteristics is known, but they closely match the elements found in the contemporary cobalt source at Erzgebirge in Germany. Textual evidence has been interpreted to suggest that some enamel pigment technologies were transferred from Europe to China, but this is the first analytical evidence to be found that an enamel pigment itself was imported. It is possible that this pigment was imported in the form of cobalt coloured glass, or smalt, which might account for its use in enamels, but not in an underglaze, where the colour might be susceptible to running. Furthermore, the European cobalt would have given a purer shade of blue than the manganese-rich Chinese cobalt.

Introduction

Cobalt is a strong colorant used in many areas of the world for the production of pigments and blue glass and glazes. Its earliest use is probably in Egypt in the Late Bronze Age, around 16th century BC. Its first use in China was in the Spring and Autumn period (770–475 BCE) when it was used as a colouring agent in glazed beads then later in low-firing glazes on Tang sancai and blue glazed earthenwares. Its first use in Chinese glass dates back to the Han Dynasty, while the earliest Chinese example of the use of cobalt as an underglaze pigment comes from the ninth century, Tang port of Yangzhou City (Wang et al., 1993). It was perfected in the blue and white porcelain of the Yuan dynasty in the early fourteenth century CE, and the technology was adopted at Jingdezhen, which went on to become the most important kiln site in China, effectively a city devoted to the production of porcelain (Tichane, 1983). Chinese blue and white porcelain represents one of the most successful and influential developments in the history of ceramic technology. A convergence of the technologies of high-fired white stoneware and underglaze painting with a cobalt pigment, it became a major component of Chinese porcelain production and was particularly important as an export ware, initially to the Islamic world and later to Europe (Medley, 1989, p. 178). It has been emulated by industries across the world, and remains commercially important today. Here new data are reported which demonstrate for the first time that European cobalt sources played an important role in the development of Chinese enamelled porcelains in the eighteenth century.

Cobalt has attracted archaeometric attention because the relatively limited number of sources that were accessible to early craftsmen, along with the variable compositions of the ores, makes it possible to characterise and attribute the pigments to their region or even mine of origin (Gratuze, 2013). In particular, the clear interplay of style and technology between the blue and white wares of China and the Near East from the Tang to Ming periods (7th-17th centuries (Medley, 1989, Rawson, 1984, Vainker, 1989)) has led to increasingly sophisticated analytical studies with a view to determining the source of cobalt and contributing to an understanding of the processes of technological transfer and innovation (Kerr and Wood, 2004, Wen and Pollard, 2016; Wen et al., 2007, Zhu et al., 2015).

The application of low-firing lead-rich coloured enamels over the glaze of previously high-fired stonewares and porcelains can be traced back to the end of the 12th to the beginning of the 13th Century (Medley, 1989, Wood, 1999, Kerr and Wood, 2004). In China they were first applied onto white slipped high-firing, glazed stonewares, known as cizhou wares, and in the late 14th century the enamelling techniques used in the northern cizhou kilns spread to Jingdezhen in the south (Wood, 1999). In the Qing dynasty (1644–1911) in the reign of the Kangxi emperor (1672–1722) the initial palette of the famille verte family, known in Chinese as wucai or five-colour was developed, comprising copper-green, iron-yellow, iron-red and turquoise overglaze enamels on porcelain decorated with underglaze cobalt (e.g. Medley, 1989, Vainker, 1989, p. 202).

The Kangxi reign (1662–1722) was a period of great stability and support for the craft industries, including an emphasis on painted enamel work on glass and metal, as well as ceramic, which was driven by the emperor himself. Workshops were attached to the Imperial Court in Beijing and foreign craftsmen were sought to develop techniques. Late in the seventeenth century the mature famille verte palette, including for the first time an overglaze cobalt blue enamel, was developed (Vainker, 1989). Towards the very end of the Kangxi period (Sato, 1981, Vainker, 1989), extensive development work in the Palace workshops in Beijing, discussed in detail by Kerr and Wood (2004) and also by Curtis (2009) led to the development of the famille rose group of enamels, which included a red based upon colloidal gold and an arsenic opaque white, which in mixing could produce a wide range of red and pink shades (Fig. 1). This palette appears to have been transferred for production at the Imperial kilns in Jingdezhen at the beginning of the reign of the succeeding emperor, Yongzheng (1722–1735). In addition to the high artistic quality of some of the ceramics, several characteristics of famille rose or fencai have attracted scholarly attention. The development of a gold-based pink at this time corresponds with the development of gold ruby glass in Europe, the practical application of which is particularly associated with the German chemist Johann Kunckel (Hunt, 1976). Europeans with knowledge and skills in glass and enamel production were attached to the Chinese Imperial Court and workshops were established, for example the glass workshop headed by the Jesuit missionary Kilian Stumpf in 1697 (Curtis, 1993). Furthermore, one of the terms by which the famille rose palette was known to the Chinese craftsmen was “foreign colours” (yangcai), and the official list of porcelain produced at Jingdezhen in the Yongzheng reign refers to the use of European or foreign decoration on at least six occasions (Bushell, 1896). All of this led to the idea that the famille rose palette was heavily influenced by European practice and possibly that the technology itself was transferred. However, limited analytical work has so far failed to identify any unambiguously European compositions on famille rose pieces (Kingery and Vandiver, 1986) and furthermore has suggested a strong link with compositions of earlier Chinese cloisonné enamels on metalwork (Henderson, 1989, Kerr and Wood, 2004, Mills and Kerr, 1999, Vainker, 1989). The influences on the development of famille rose therefore continue to be a subject of significant interest.

Our understanding of porcelain production and technology in the Qing Dynasty has been surprisingly dependent upon the account of a single person, Père d’Entrecolles, a French Jesuit missionary. Through conversations with the craftsmen and direct observation, d’Entrecolles was able to document many aspects of industrial practice, in two famous letters dated 1712 and 1722, which attracted wide attention in the eighteenth century as Europeans attempted to discover the secret of porcelain. English translations in print are provided by Burton (1906; slightly abridged) and Tichane (1983) with an on-line version provided at www.gutenberg.com. Significantly for the present work, d’Entrecolles's last communication from Jingdezhen was more-or-less at the time when famille rose production was introduced at Jingdezhen, but he does make some interesting observations about earlier enamels and cobalt.

Cobalt blue was such a widespread colour in Chinese ceramic production from the fourteenth century onwards that a critical role in the development of the enamel palette has not been considered in detail. However, there are some tantalising indications that production of a cobalt blue enamel was not straightforward. Firstly, there is the fact that it was the very last of the overglaze colours to be added to the earlier famille verte palette (Vainker, 1989, p. 202). Secondly, the analysis of famille verte enamels by Kingery and Vandiver (1986) reveals the cobalt blue to be the only colour with an elevated potash content of around 6% relative to less than 0.5% for the other colours. With some hindsight, this suggests a deliberate addition of potassium to the blue and a significant difference in the technology of the base glass relative to the other colours at that time.

The present paper reports new quantitative results for the cobalt on the later blue-and-white ceramics of the Qing Dynasty (1644–1912). While most are agreed that by the end of Ming times the pigments used on Chinese underglaze blue were obtained from Chinese sources (Wen and Pollard, 2016, Wen et al., 2007, Zhu et al., 2015), our results suggest that the situation under the Qing was more complex. In particular, we focus on the pigments on the polychrome enamelled wares which were extensively exported to Europe during this period.

The blue colour produced by cobalt-based pigments can be due to the presence of cobalt in both crystalline and solution-ionic forms. As the Co³⁺ ion is not stable in the temperature range required for glass melting, only those cobalt compounds which are derived from the divalent cobalt ion Co²⁺ are of interest in glass technology (metallic Co assumes a significant role only in the field of enamel on metal, where it contributes to the adherence of the ground coats) (Weyl, 1951, p. 170). In particular, in alkaline glazes, Co²⁺ ions in tetrahedral coordination (i.e. present in the vitreous structure as glass formers, in the form of CoO₄ complexes) give rise to blues or blue-purples (or blue hues in lead-based matrices), while in the octahedral coordination (Co²⁺ ions are inserted in the position occupied by alkali ions, CoO₆ complexes) confer pink hues to the glass (Weyl, 1951, pp. 179–80, 182–4). Cobalt is one of the most stable and powerful colouring agents and saturated blue tints in common glassy systems occur for CoO concentrations as low as 0.25% (noticeable blues are already observed at levels of c. 0.005% CoO) (Kerr and Wood, 2004, Weyl, 1951, pp. 179–80). In Chinese blue underglazes CoO is usually found at levels of about 0.1–1% (Kerr and Wood, 2004).

Cobalt does not exist as a native metal, though there are many cobalt-bearing minerals from which it can be extracted (Henderson, 2000, p. 30). The analysis of the impurities naturally occurring in the cobalt ores (e.g. iron, copper, manganese, nickel, arsenic, sulphur, bismuth) might therefore provide a valuable support in revealing the cobalt sources employed by the ancient craftsmen. For example, the association of arsenic and sulphur (and sometimes zinc) may suggest the use of cobaltite (CoAsS) or smaltite (CoAs₂), while nickel and arsenic of the minerals erythrite (Co₃(AsO₄)₂8H₂O) or skutterudite ((Co,Ni)As_3–x), manganese of the mineral asbolane (Co,Ni)_1–y(MnO₂)_2–x(OH)_2–2y+2x n(H₂O). Several cobalt-compounds can also contain significant amount copper. Finally, blue compounds could also be obtained from cobalt, nickel, iron and copper-rich residues after separating bismuth from its ores (Frank, 1982).