The floral pattern called Bao Xiang hua is called in the West 'a lotus flower pattern', but have you ever seen a lotus with that kind of leaves and vines? The Bao Xiang is not a lotus flower: it exists in traditional Chinese culture like dragons and phoenixes, provided with a mythical status and no actual existence in nature. It's, indeed, a combination of various floral elements (lotus, peony, chrysanthemum, and pomegranate); it has a Buddhist origin (it's called sometimes 'the Buddha's rose') and was used as a decorative element since the Tang Dynasty era.
The chrysanthemum, the flower of autumn in China, is a widespread symbol of nobility, long life, and duration, while in many European countries is the flower of the dead, associated with mourning.
The dragon is a complex symbol in traditional Chinese culture. Simplifying, we can say that it's a positive symbol of yang, male prowess, fertility, power, strength, and divine rule. It is often depicted creating clouds with its breath, riding clouds, or playing among them, causing beneficial rain to fall. «From the Han Dynasty (206 BC–220 AD) onwards, the dragon is also the symbol of the Emperor, the Son of Heaven» (Wolfram Eberhard, A Dictionary of Chinese Symbols, see Bibliography). During the Yuan Dynasty, the five-claw dragon became an imperial symbol and a decorative motif reserved for the Emperor alone, while the four-claw and three-claw dragon decorations were reserved for objects and robes made for princes and noble officials.
The dragon is often depicted together with the phoenix, a mythical creature representing its female, ying counterpart. Next to the dragon-Emperor, the phoenix represents the Empress. Therefore, the Chinese phoenix has nothing to do with the legendary, immortal bird symbol of bliss and eternal rebirth of Greek and Egyptian antiquity, Christian tradition, and Arabian mythology.
THE TECHNICAL SIDE
The David Vases were porcelain in the strict (Western) sense, not porcelaneous stoneware like celadon pieces.
The body of all blue and white porcelain pieces was made by mixing petuntse (porcelain stone) with kaolin (whose name derives from Gaolin Hill near Jingdezhen) in varying proportions, depending on the shape, dimensions, and finesse of porcelain to be produced. Once ready and naturally dried, the pieces were brush painted with cobalt-blue pigment mixed with water, then coated with a clear glaze, and finally fired at high temperature (+ 1300° C). The painted decoration was applied directly on the clay body, before the firing phase, which was always a single one (celadon glazed pieces could be fired more than once). That's why these porcelain pieces are said to show an 'underglaze' cobalt decoration.
As Suzanne G. Valenstein highlighted, the recent laboratory analyses of several categories of Chinese porcelain have revealed that the raw materials used in porcelain production varied considerably among different kiln centers; even at Jingdezhen, the composition of porcelain bodies changed over the centuries. According to Jing Yang and Annika Waenerberg, «during the Yuan (1271–1368) and Ming (1368–1644) dynasties, the using amount of raw materials was 10–25% kaolin and 90–75% porcelain stone for the blue and white porcelain bodies, whereas during the Qing dynasty (1644–1911) 30–60% kaolin and 70–40% porcelain stone was used» (Jing Yang and Annika Waenerberg, Blue and White Porcelain, see Bibliography)
As for the glaze, it was a clear colorless one, different from that used for qingbai and Shufu/luanbai wares: during the Yuan Dynasty, the glaze on the blue and white porcelain pieces contained 8-10% of calcium oxide, while qingbai 12-13%, and shufu/luanbai 5-6%.
The cobalt blue was imported from Persia - present-day Iran, at the time the Ilkhanate or Iranzamin ruled by the Mongol House of Hulagu, a descendant of Genghis Khan - via the Silk Road trade route. It came from ancient mines of metallic-lustered cobalt ore located near the little village of Qamsar, 400 km south of Tehran, in the hills above Kashan. Locally, it was called "Solaymānī" cobalt, a term which became in Chinese sumani (or sumali) qing, and it was so prized to reach twice the value of gold. The cobalt blue pigment used to paint the porcelain in Jingdezhen contained cobalt oxide and aluminum oxide and had a distinctive pale black color before the firing phase. After, it turned into an 'explosive', vibrant intense blue color on the top-quality pieces and showed a greyish tone On the low-quality ones (because of greater dilution).
The Persian cobalt imported and used during the Yuan and the early Ming dynasties was rich in iron oxide, an impurity that produced the so-called “heaped and piled” effect after firing: spots and small areas of darker color with a black-purple tone on the fired, glazed surface, as in the pictures below.