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Making of Ceramic - Glaze

Glaze: enhancing ceramic with funtionality and asethetic

After the ware, or the pi(坯) is shaped, it will go to the first time firing and become biscuit earthenware. In this stage, the ware is rough, low in density and without any colour but the natural colour from the clay. To enhance the nature of biscuit earthenware, glaze, an impervious layer or coating of a vitreous substance, is needed to apply to the surface of them. Apart from coloring and decoration, glaze serves to seal the inherent porosity of biscuit earthenware and waterproof the ceramic. It gives a tougher surface and enhances functionality.

The technique of glazing is precious knowledge inherited by predecessors. Indeed, it is a very scientific procedure. Vitrification is the key of glazing process which turn a mixture of materials into a hard and glass-like texture. In terms of materials of the glaze, it contains not only the clay but ceramic flux in order to lower the melting temperature of the glaze materials. Silica is the most important ingredient which will be the main glass former. Metal oxides such as sodium and calcium could help promoting partial liquefaction of the glaze materials during firing. By mixing different types of powdered minerals, it will produce variations in color and texture.

Figure: Biscuit earthenwares - fired once without coating glazeSource: Rainbo.hk

Figure: Silica powder source: Internet resource

Figure: With the same basic formula of the glaze but add with different types and amount of substance, we can get a variety of colour after firing. Source: Ceramic Art Network

Kerr, R. & Wood, N. (2004). [ Fung-hsien chhing-pai, copper-green and copper-red glazes]. Science and Civilisation in China, Volume 5, Chemistry and Chemical Technology, Part 12, Ceramic Technology. Cambridge: Cambridge University Press. pp. 657.

Figure: Applying glaze on biscuit earthenware by brush.Source: The curatorial team

The most common method to apply the glaze to the ware is to dip the ware directly to the aqueous mixture. Pouring the glaze over the ware, spraying it onto the ware or drawing it directly with a brush or other tools are also the common technique. It is not limited to fire the glazed ware once only. Instead, to build more layers of colour or texture, artisans may applying the glaze serval times.

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Each dynasty has its significant glaze styles attributed to technology development and the transformation of aesthetic value. How much do you know? Let's learn the representative glazes in the following three dynasties, and be an expert next time when you enter the museum!

Tang dynasty 唐代 (618-907)

Sancai, or three-colour ware (三彩)

Although Sancai literally means three colors, generally indicating the basic colour green, white and yellow, more colour could also be featured such as brown and blue. It is a type of lead-glazed earthenware (lead oxide as the principal flux and mixed with quartz) and fired at around 800 °C. By adding other metal oxides, the glaze will turn to different colour: copper for green, iron for brownish-yellow and cobalt for blue. However, it is observed that some places of the ceramic bodies were deliberately unglazed. It is because the glaze may mix during firing that would ruin the facial features. Thus, artisans replaced the glaze by the pigment in those parts, which has already lost after hundreds of years while the glaze still in very good condition.

Figure: Tomb Figure of a Bactrian Camel, earthenware with sancai glazeDate: early to mid- 8th century.Source: Philadelphia Museum of Art

Figure: Figure of a Lady Wearing a Long Shawl, earthenware with sancai glaze and pigmentDate: late 7th-first half of the 8th century. Source: The Metropolitan Museum of Art

Figure: Vase with Dragonfish Handles, porcelain with relief decoration under celadon glaze (Longquan ware)Date: 12th-13th centurySource: The Metropolitan Museum of Art

Figure: Bowl, porcelain with incised design under glaze, the rim bound with copper (Ding ware)Date: 11th-early 12th century Source: Asia Society Museum

Song dynasty 宋代 (960-1279)

Period of subtle

In general, the glazes of ceramic in Song periods is well-known for the beauty of simplicity and elegance. They tend to be subtle and monochromatic with cool-toned glazes. The most famous ceramics come from five kilns patronized by the court: Ru (汝), Guan (官), Ge (哥), Jun (鈞), Ding (定) kilns, also the pedestrian kilns such as Cizhou (磁州) and Longquan (龍泉).

Each of the kilns has their prominent glaze style. For example, Ding ware is typical for its ivory-toned white pieces with impressed or carved patterns. Black or brown glazes were sometimes produced alongside the fringe. Besides, celadon glaze is especially famous for Longquan kilns. The pale jade colour comes from iron oxide fired in a reducing atmosphere. The wares can get the best green or blue colours when they are fired the range over 1,250 °C.

Qing dynasty 清代 (1644–1911/12)

The flourishing era

Ceramic technology has maturely developed in Qing dynasty. Blue and white porcelain is a white porcelain underglaze with a blue pigment, usually made from cobalt oxide that used to be rare in previous dynasties. It has developed since Tang dynasty and attained its peak in Qing dynasty. The pattern is very delicate which is commonly applied by hand.

The pattern is also detailed for polychrome ware, usually refers to families groups, including famille jaune, noire, rose and verte depending on the dominant palettes of enamel colours on porcelain. For instance, Famille rose (粉彩) has a greater range of colour and tone, enabling the depiction of more complex images such as flowers, figures, landscape and manifold patterns.