Comparison of iron rust spots of underglaze blue porcelains

◎ Underglaze blue porcelain◎

Imported pigment – Su-ma-li blue

An intertwined relationship connects imported pigment (Su-ma-li Blue), Jingdezhen, and underglaze-blue in Yuan dynasty. The primary use of imported Su-ma-li blue pigment was during late Yuan dynasty (1279-1368) and early Ming dynasty (1368-1644). In Wang, Shi-mao’s book “Kui-tian-wai-chen,” he describes Su-ma-li Blue used imported from West Asia, and stated “Our court specially established porcelain manufacture in Jingdezhen of Fuliang county. Imperial Porcelains made in Yong-le and Xuan-de reigns possessed the characteristics of frequently used sweet white color with orange peel effect, decorative pigment of Su-ma-li blue, and precious bright red color.” Su-ma-li blue pigment contains high concentration of iron and low concentration of manganese and is different from local pigment which contains high concentration of manganese and low concentration of iron. Due to the natural black of iron oxide, underglaze blue presents dense blue with black spots after firing. This is the most obvious feature of imported pigment, which presents gorgeous, pretty, dark, gradated, and diffused tinge. Under proper firing temperature, the pigment appears sapphire luster with black spots where there are silver spots in dark glazed area. Mostly, the more dark color underglaze blue presents, the more amount crystallized spots appear. Obvious iron rust spots of silver color are sometimes embedded into clay with uneven touch. These underglaze blue porcelains have been mainstream products in Jingdezhen since Yuan dynasty (1279-1368).

◎ Micrography and appraisement of genuine and fake porcelains◎

=> Photo A

= >Photo B

= > Magnification A

= > Magnification B

Source A: DCL-CARD / Meip’ing vase with underglaze blue decoration of clouds and dragons, Ming dynasty (1279-1368)

Source B: DCL-CARD / Modern phony-Shard of dish with underglaze blue decoration of figures, Yuan dynasty (1279-1368).

Illustration A: Su-ma-li blue pigment contains high amount of iron, so blackish or greenish brown iron rust spots remains on the surface of glaze. Iron rust spots of genuine porcelain formed gradually after hundred years. The spots naturally emerged and were embedded into clay. The slightly diffused spots usually appeared in deep glazing area and had vague borderline.

Illustration B: The imitation of Su-ma-li blue is adding iron oxide in pigment. The artificial material presents angular shape and has clear borderline with underglaze blue pigment. Fake iron rust spots didn’t have varied shades and distributed irregular both in shallow and deep glazing areas.

◎ Reference:

1. Zhang, Hong-wei. Ancient Chinese Ceramics Research, Vol. 10, Beijing: Forbidden City, 2004.
2. Zhang, Pu-sheng. Blue and White Porcelain Appraisement, Beijing: Beijing Library, Jan. 1995.
3. Liu Ru-shui. Appreciation of China, Taipei: Shuchuan, Aug. 2004.
4. Ma, Xi-gui. Chinese Blue and White Porcelain, Shanghai: Shanghai Gu Ji, 1999.
5. Yang Jia-luo. A record of Ceramics, Vol. 1&2, Taipei: World Bookstore, 1974.
6. Lan Pu/ Zheng, Ting-gui. Pottery Record of Jingdezhen, Shandong: Hua-bao, 2004.
7. She Cheng. Development of Blue and White Porcelain in Ming Dynasty and Art Research, Taipei: Wen Shi zhe, Mar. 1986.
8. Li, Hui-bing. Appraisement Foundations of Chinese Porcelain, Beijing: Forbidden City, 2001.
9. Liu, Liang You. Research of Antique Porcelain, Taipei: Youth Culture, Jan. 1988.
10. Zhu Yan. Pottery, 1774.