Chinese ceramics — An expert guide to glazes
From cool creams and greens to fabulous purples, the decorative glazes of Chinese ceramics vary hugely through the dynasties — as specialist Jessica Chang explains
Chinese ceramics vary greatly in their glazes and decoration, and the many technical terms involved can be daunting for collectors who are new to the category. So what is a glaze?
‘In general, glaze is an impervious layer or glass-like coating which is applied to a ceramic body, then fused through firing,' explains specialist Jessica Chang. 'Glaze can be used as a colourant, as decoration or to waterproof ceramic. The most important ingredient in the glaze is silica, and the variations in type depend on the addition of other materials.’
These additions include copper, aluminium and other ingredients that can affect the glaze’s viscosity, colour and texture. Glazes can be applied to the ceramic bodies either before or after firing — techniques known respectively as underglaze and overglaze decoration.
Glazes were originally used for practical reasons because many stoneware and earthenware pots were too porous to act as containers, but aesthetics also played a part. 'The glaze is also very pleasing to the eye, so even though porcelain doesn't have that issue of porosity, it is still applied for decorative effect,' notes Chang.
The first Chinese ceramics — handbuilt earthenware pots — date back tens of thousands of years to the Palaeolithic period, but it was not until the Sui and Tang dynasties (581–907 AD) that technology developed sufficiently for craftsmen to be able to produce uniform vessels on the wheel and colourful glazes in the kiln.
Sancai literally means three colours, but actually it’s a general term because you see examples of Sancai in which there are more than three colours. Usually these basic colours will be green, cream and amber — known as ‘egg and spinach’ in the West — but the glaze could also feature brown, blue and purple.
During the Tang dynasty (618–907 AD), Sancai wares were widely used for burial goods such as vessels and figurines. ‘On these figures you will see a lot of places that have been deliberately left unglazed,’ explains Chang. ‘Because the glaze is really runny all these different colours will mix during firing — which is not ideal for facial features. So they left the features unglazed, and later painted them in with coloured pigments. With many of the pieces we see today, the pigment is lost because it's mostly composed of organic materials, but the glaze remains vibrant.'
The Song dynasty, in contrast to its predecessor, the Tang, is known for monochrome, very cool-toned glazes which resemble jade and silver, snow and ice. Song dynasty monochrome glazes have a very modern feel to them, even though they're more than 1,000 years old. I never fail to be amazed at how they can achieve that very harmonious balance between the shape and the glaze,' comments Chang. The most famous Song ceramics come from five main kilns: Ru, Guan, Ge, Ding and Jun.
A small Ru-type foliate dish. Yongzheng period (1723-1735). 5⅝ in (14.3 cm) diam. Estimate: £10,000-15,000. Sold for £75,000 on 8 November 2016 at Christie’s London
‘The most sought-after pieces in the current market are porcelain wares produced in the Ru kiln,’ Chang explains. ‘These are extremely rare; currently there are only around 70 known pieces in the world.’
This glaze is particularly special because it contains agate, which was extremely difficult to source at the time. Similar to Longquan Celadon ware, these pieces contain some iron oxide, which lends them jade-like tones. The wares were often further enhanced with the introduction of crackles — a result of the glaze cooling faster than the body and contracting on the surface.
‘We talk about Ge and Guan as if they are two different glazes, but there is much scholarly debate about whether the Ge kiln really existed,’ says Chang. ‘All debate aside, it is generally accepted that both Guan wares and those attributed to Ge have a distinctive crackle glaze. The Chinese call this jinsitiexian, meaning gold floss and iron thread, which refers to the two sets of lines visible in the glaze — one finer and golden in tone and the other darker and thicker.’
'Ding ware is notable for its ivory-toned white pieces with impressed or carved decoration,' says Chang. 'Black or brown glazes were also produced alongside the white wares and are very rare.'
A distinct trait of Ding ware is the appearance of ‘tear marks’. 'These are streaks — like teardrops — that appear on some pieces,’ explains Chang. ‘They are a good indication a piece is genuine, as they don't normally appear on later imitations.'
‘Jun glaze is more vibrant when compared to glazes from the other four kiln sites,' explains Chang. 'Jun ware is known for its very thick, bright bluish glaze, which varies from piece to piece. This blue colour is not derived from a pigment, but is actually an optical illusion resulting from a phenomenon called liquid-liquid phase separation, which results in an opalescent effect.' Some Jun ware also has decorative reddish or purple splashes as a result of copper in the glaze.
'Also worth noting are what the Chinese call "earthworm tracks", which appear on many Jun pieces, resembling the trails left in soil by earthworms. Rarely visible on later imitations, these markings are a good indication that a piece is genuine.'
‘In the West the term "celadon" is used to describe any Asian porcelain that has a pale jade colour,’ says Chang.
Celadon glaze originated in China, where famous producers included the Yue and Longquan kilns in Zhejiang province. The technique later spread as far as Korea, Japan and Thailand. Despite their name, Celadon glazes can range in colour from white and grey to blue and yellow, according to how thickly the glaze was applied, the sort of clay used, the ingredients of the glaze, and how the wares were fired.
In Japan, Celadon wares with a bluish tone are particularly revered, their colour indicating that they were produced in Longquan, Zhejiang province during the Southern Song dynasty (1127-1279).
The term ‘blue and white’ encompasses a wide range of styles that all employ blue and white decoration, explains Jessica. 'Blue and white consists of a cobalt-blue underglaze decoration, laid over the white porcelain body, while the glaze is actually transparent,’ says Chang.
Beginning in the 9th century and stretching far into the Qing dynasty (1644–1912), the style is perhaps the most popular of Chinese ceramics and is featured on some of the world’s most valuable pieces. ‘Many consider pieces from the Kangxi period, during the Qing dynasty, to be the best,’ says the specialist, ‘but the Yuan (1279–1368 AD) and Ming (1368–1644 AD) blue and white ceramics also have great historic, aesthetic and monetary value.’
Kangxi pieces are valued for their light body, vibrant blue colour, and style of painting which Chang describes as ‘more controlled and very refined’. Cobalt blue — considered a precious commodity — was imported from Persia by Muslim traders, and many of these early wares show the influence of Islamic decoration. Blue and white ware was first exported to Europe in the 17th century by the Dutch East India Company, sparking a craze for the style and spawning a number of imitations, such as the ubiquitous Willow pattern.
'Flambé is the name given to the high-fire iridescent glaze that has blue, purple and reddish colours. These are the result of copper or other metallic materials that break up on the surface of the very runny glaze, a method which produces unique pieces,' explains Chang.
‘It is impossible to find two identical pieces even in the same shape, because it’s not controllable, which makes it very exciting,’ she continues. Although these pieces hold great abstract appeal, they are often not as highly prized as the elaborate designs of the Ming and Qing imperial wares. ‘Flambé is not a typical Chinese glaze’, Chang says. ‘It’s abstract, a different aesthetic — but it is one of my favourite glazes because of its vibrant tones. It deserves more appreciation.'
Wucai, meaning 'five colours', originally referred to porcelain decorated in a palette of five colours dating from the Ming period (1368-1642), especially during the reign of emperors Jiajing (1522-66) and Wanli (1573-1619). 'Because blue enamel did not exist during the Ming dynasty, Wucai porcelain was made by glazing ceramic pieces after they had been fired once, with underglazed cobalt blue decoration,' Chang notes. 'It was then fired a second time with the overglazed decoration, which featured a variety of colours including red, green, blue, yellow and purple.'
Later in the Kangxi period, Wucai wares evolved to become what Western scholars now refer to as famille verte, French for 'the green family'. During this period, the palette developed to include clear greens, with enamels of other colours used for decoration.
Around the end of the Kangxi period, famille rose, or 'pink family' enamels, were introduced in China. Composed largely of opaque white and pink enamels derived from colloidal gold, introduced through the Jesuits serving at the Qing court, this new palette became very popular during the subsequent Yongzheng and Qianlong reigns. ‘The Yongzheng famille rose has a delicate and feminine quality that is unique to this period; many connoisseurs consider it to be the best of its kind,’ observes Chang.
‘In Chinese there are different terms for the peach-bloom glaze, such as "bean red", "beauty’s blush”, “baby’s face” or “drunken beauty”, to describe the particular kind of blush tone that resembles human skin,’ says Chang.
This blush colour is highly sought-after by collectors, particularly if there are green speckles on the piece. To achieve this green effect, a glaze containing copper needed to be applied very precisely, before being fired with great care. This glaze is unique to the Kangxi period and tends to be used for smaller pieces, such as the objects found in a scholar’s studio.