This beautiful tianqiuping has been given a particularly jewel-like sapphire blue glaze, which serves to emphasise the elegance of the form of the vessel. The rich cobalt blue seen on the current vase is sometimes referred to as 'sacrificial blue'. This name derives from the use of vessels bearing this colour glaze during sacrifices at the Imperial Altar of Heaven. In AD 1369 the first Ming dynasty emperor Hongwu issued an edict declaring that the vessels used on the Imperial altars should henceforth be made of porcelain. Each altar was associated with a specific colour of porcelain, and in addition to blue being used on the Altar of Heaven, red was used on the Altar of the Sun, yellow on the Altar of Earth, and white on the Altar of the Moon.
The potters at the Imperial kilns in the 18th century were highly skilled and the technology used to produce porcelains was highly developed. By the 18th century refining techniques were also quite sophisticated and the additional elements in the cobalt ore to be used in colouring rich cobalt blue glazes, like the glaze on the current vessel, could largely be controlled. Elements such as iron and manganese, for example, had considerable effect on the colour of the fired glaze. In addition, pigments that were high in alumina tended to develop cobalt aluminates in firing, resulting a cooler blue tones, while pigments which contained more silica produced cobalt silicates, resulting in warmer, more purplish, blues.
A similar cobalt blue globular bottle vase, but dating to the Qianlong reign, was included in the exhibition The Wonders of the Potter's Palette, Hong Kong Museum of Art, 1984, no. 85. A smaller cobalt blue bottle vase with less globular body is in the Baur Collection, Geneva (illustrated by J. Ayers and M. Sato in Ceramic Art of the World - Volume 15 - Ch'ing Dynasty, Shogakukan, Tokyo, 1983, p. 199, no. 272). It is rare to find a cobalt blue-glazed vase of this form with a Yongzheng mark, however a larger vase and of slightly different proportion, also bearing a Yongzheng seal mark in the Wang Xing Lou Collection is illustrated in Imperial Perfection - The Palace Porcelain of Three Chinese Emperors, Hong Kong, 2004, p. 224, no. 87, and was sold at Sotheby's, Hong Kong, 20 November 1984, lot 486. In the same sale was a cobalt blue vase, of similar size and shape to the current vessel, but bearing a Qianlong seal mark (lot 487).