A pigment is a finely ground mineral ore selected for its color. Mixed with water, it can be used to paint decoration directly onto the surface of a clay vessel or over a coating of slip. When pigment is painted onto stoneware (with or without a slip coating), it is usually covered with a colorless transparent or translucent glaze that preserves it and enhances its color. Pigment can also be mixed into a low-temperature or high-temperature glaze to tint it.
The basic pigments used by potters in Mainland Southeast Asia, as elsewhere in the world, were iron and cobalt. Iron is widely available in natural forms, usually associated with clay, while cobalt is rare. Iron pigment can produce various shades from red orange to brownish black, depending on the form of iron and the admixed minerals. Cobalt is the source of shades of medium to deep blue. As used for ceramic decorations, these pigments are sometimes called by their finished appearance as "black" ("underglaze black") and "blue" ("underglaze blue" or "blue-and-white"). In this catalogue they are named by their primary colorants, although it is important to recognize that pre-industrial potters were using impure rocks as pigment sources. Inevitably the rocks included associated ores (such as manganese found with cobalt) that affected the color tint.
Copper was used only rarely as a pigment. It probably was obtained in the form of filings or other waste products from metalworking foundries.
To the extent that the decorations executed on ceramics in various regions of Mainland Southeast Asia are painted, they are related to indigenous traditions of painting (and writing), such as murals or illustrated manuscripts on palm leaf or paper. An intriguing aspect of painted ceramic decoration is the nature of the brush employed. Some forms of decoration on Sawankhalok and Sukhothai ceramics appear to be executed with a stiff brush (possibly softened plant fiber) that leaves crisp, blunted ends to the lines. Elsewhere, in Kalong or at the Red River Delta kilns in North Vietnam, the soft, flexible Chinese-style animal-hair brush must have been employed, judging from the quality of line and outline.
Until the advent of industrial processing, iron oxide pigment was most easily available in iron-bearing clays-and therefore technically a slip. Painting on early pots, such as late Ban Chiang wares, made use of iron slip rather than iron pigment. (The early use of iron oxide for decoration is discussed under Slips.) Iron pigment used for painted decoration on stoneware was probably associated with some amount of clay, but it will be discussed here for ease of comparison with cobalt.
Painted iron decoration covered by clear glaze (or possibly applied over it) appeared on stoneware made at the Dai La kiln site west of Hanoi in the fourteenth century (Bui and Nguyen-Long 2001, 106). Some dishes and bowls made at the Binh Dinh (Vijaya) kilns in Central Vietnam also bore iron decoration under the glaze (Morimoto 1993). Similar underglaze decoration on stoneware was produced at the Sawankhalok kilns on MON-associated stoneware (MASW). This production occurred in the early decades of the fifteenth century, according to shipwreck evidence (Brown 2004). Around the same time, the Sukhothai kilns produced wares with iron decoration over thick white slip, which became their standard mode, while the Sawankhalok kilns shifted by mid-fourteenth century to a focus on celadon glaze. The San Kamphaeng kilns in Lan Na also used iron decoration on some wares.
It is possible that the use of iron-painted decoration in the fourteenth and fifteenth centuries represented a response to iron-decorated wares imported from southern Chinese kilns, such as the Haikang kilns in southern Guangdong province (Tang 1990; Morimoto 1993, 56). By contrast, a later (sixteenth-century) phase of iron decoration at Sawankhalok and Kalong appears to be an attempt to replicate (in the absence of the actual blue pigment) the decoration executed with cobalt on wares from North Vietnam and southern China. Similar iron decoration appears on very few ceramics from Lower Burma dating to the sixteenth century (Hein 2006).
Unlike iron pigment, which may be fired alone, cobalt decoration fired without a protective glaze covering turns black rather than the desired blue. The use of cobalt pigment was relatively rare in Mainland Southeast Asia, presumably due to the scarcity of the element itself, and was confined mainly to northern Vietnamese kilns near Hanoi (Thanh Long) and to the Red River Delta, where it was used by the opening years of the fifteenth century, if not earlier (Bui and Nguyen-Long 2001, 106). Its popularity was likely a response to Chinese cobalt-decorated porcelain that had appeared a century or so earlier. Analysis of cobalt decoration on samples suggested slightly different sources of cobalt for Vietnamese and Chinese (Jingdezhen) wares, but the source of the cobalt used in Vietnam is not yet identified (Morimoto and Yamazaki 2001,36), although Yunnan has been suggested.
Cobalt was used as a pigment for decoration and as a colorant for earthenware ceramics made in Arakan, Upper Burma (Tsuda 1999; 2004; 2005, 60).
Copper pigment began to be used relatively late in the history of ceramic production in Mainland Southeast Asia and was never very widespread. People in the region might have been familiar with the turquoise copper-tinted glaze on earthenware made in Iraq and brought to the region (for example, to Angkor) in the ninth century.
The earliest use of copper in Mainland Southeast Asian ceramics appears to be the copper-tinted "apple green" high-temperature glazes used on some pieces made at kilns in the Red River Delta in the fourteenth and fifteenth centuries. Rosemary Scott and Rose Kerr have suggested that the source of this innovation may have been bowls from Chinese kilns in Guangxi province, which bore translucent copper-green glaze over molded interior designs in imitation of Yaozhou ware from the north (Scott and Kerr 1993, 31-32).
In a separate development, copper was the colorant for green lead-silicate enamels used, along with red and yellow (and sometimes gold), for painting decoration over the glaze. The recovery of enamel-decorated northern Vietnamese wares from the Cu Lao Cham (Hoi An) shipwreck shows that such decoration was used in Vietnam by the late fifteenth century (Guy 2000). It may have been introduced from the Zhangzhou kilns in southern Fujian province, which also exported stoneware vessels decorated with copper-green, manganese-purple, and iron-yellow lead glazes. Some kilns in the Tung Man group within the Kalong kiln complex briefly used copper-green lead glaze on small jars and other objects, and it is hard to dismiss the possibility of some direct interaction with Zhangzhou technology (Shaw 1987, 59 and 71).
Sherds of bowls bearing turquoise-blue copper-tinted low-temperature glaze-very much in a West Asian tradition-were recovered from the Phayagyi kiln site in the Irrawaddy Delta (Tsuda 2004, 220). At as-yet-unidentified kilns in Lower Burma, copper was used in a distinctive manner to tint white tin-opacified lead glaze. The milky-green glaze was applied over the entire vessel or else trailed using a tube applicator over unfired white glaze to make pictorial decoration. (The process is similar to the use of white slip to decorate black-glazed jars from the same area.) The shapes of the vessels and the format of the in-glaze decoration suggest a relationship to Chinese cobalt-decorated porcelain of the sixteenth (or early seventeenth) century, and the copper pigment appears to have been used as an alternative to costly or unobtainable cobalt.
Copper-green glazes reappeared in the region in the eighteenth and nineteenth centuries on utilitarian wares and roof tiles made at the Shiwan (Shekwan) kilns in Guangdong province. The glaze was also used at kilns opened in South Vietnam by immigrant potters from Guangdong and at kilns in coastal Central Vietnam such as Tuy Hoa, which applied the glaze to lime-paste containers, bottles, and jars.