The colour blue gained special significance in the history of Chinese ceramics during the Tang dynasty (618-907). The distinctive colour in blue-glazed pottery and porcelain comes from cobalt ores imported from Persia, which were a scarce ingredient at the time and used in only limited quantities.
In the Yuan (1279-1368), Ming (1368-1644) and Qing (1644-1911) dynasties in particular, different types of cobalt ore and methods of application determined the distinctive feature of the shades of blue that appeared on blue-and-white porcelain ware.
It is believed that cobalt ores had been widely exploited in West Asia for use as pigments since as early as 2000 B.C. In China, they were first used for glassmaking during the Warring States (475-221 B.C.) period.
The flourishing of the Silk Road trade route saw imported cobalt introduced to China and its application, with other lead-based glazes, on low-fired earthenware, leading to the rapid development of three-coloured sancai wares.
The Song dynasty (960-1279) marked a high point in the production of monochrome wares, but artisans of this period regarded the use of cobalt blue as an impossibility. It was not until the Mongol-ruled Yuan dynasty that the manufacture of blue-and-white porcelain came to maturity, which resulted in richer and more complex subject matter. In part, this development had a religious component: the Mongols counted as their mythical ancestors the ‘hazy blue’ wolf and the ‘white’ fallow doe. Blue-and-white porcelain was reserved for special occasions or used for diplomatic gifts.
The Samarra Blue (sumali qing) or Sumatra Blue (suboni qing) cobalt used for Yuan wares was rich in iron, which yielded a glaze with darker blue spots. This so-called ‘heaped and piled’ effect was caused by the accumulation of iron oxide in the cobalt pigment in certain areas of the surface. Blue-and-white wares were used by local dignitaries and widely exported as diplomatic gifts and merchandise.
During the reigns of Yongle (1403-1425) and Xuande (1426-1435) in the early Ming period (1368-1644), smalt cobalt, brought by the returning fleets of Zheng He’s (1371-1433) maritime expeditions, was still the main source for blue-and-white porcelain. Subsequently, more rigorous firing processes resulted in subtle displays of ‘heap and pile’ characteristics, with varying tones of rich and brilliant cobalt blue visible in the glazed surface.
In the Hongwu period (1368-1398), the supply of imported cobalt was briefly disrupted by several foreign trade restrictions. Locally mined cobalt, which is distinguished by a high proportion of manganese, came to play an increasingly dominant role after the Xuande period (1426-1435). From the Chenghua (1465-1487) to the Zhengde (1506-1521) periods, the local cobalt yielded a softer, pale blue colour.
The mixture of imported and local cobalts
Another kind of local cobalt, called ‘Mineral Blue’ (shi qing or shizi qing), was sourced from Jiangxi province. Characterised by a dull leaden-blue colour, it was commonly used for minyao (folk kiln) blue-and-white. However, when mixed with ‘Muslim Blue’ (huiqing), the most precious type of ‘Mineral Blue’ from Central Asia, Xinjiang and Yunnan provinces, it generated a distinctive purplish-blue tone. The vividness of the glaze, ranging from violet blue to silvery blue, depended on the amount of ‘Mineral Blue’ included.
The desirability of various tones largely depended on the taste of different emperors. For example, the Xuande Emperor favoured a purplish blue colour with heaping and piling effect, while the Chenghua Emperor preferred the washy tone.
If Yuan blue-and-white was the first high point, Yongle (1403-1425) to Chenghua (1465-1487) can be considered the second, with Chongzhen (1611-1644) to Kangxi (1662-1722) — the so-called Transitional Period — being the third. Using local cobalt mined in the counties of Shaoxing, Jinhua and Quzhou in Zhejiang province, the ‘Zhejiang Blue’ (Zheliao) applied to Kangxi blue-and-white porcelain resulted in intense, bright shades of cobalt blue, with an almost three-dimensional quality.