Tang lead glazes: Sancai ware

And so to the Tang dynasty (617-908 AD), whose most famous ceramic is the glazed earthenware called sancai (“three colours”). Confusingly, there are at least four colours in traditional sancai: green, amber, white (or “straw-coloured”) and blue. The tray or platter below displays the green and amber colours, while the gorgeous horse illustrates the blue and straw shades. Some pieces may have grey, dark brown or black tones.

(Left) Sancai tray. D: 29cm. China, Tang dynasty. Met Museum, NY

(Right) Sancai horse. H: 55cm. China, Tang dynasty. National Museum of Korea 

Sancai is probably the best-known Chinese lead-based glaze, containing 55-60% lead oxide (PbO). We know now that lead is poisonous, but there were reasons for its popularity in ceramics. It is a very effective flux which helps the glaze melt and fit the pot snugly. It gives a lovely shine because PbO has a high refractive index, helping to catch and disperse light. Lead glazes can be made directly from crushed raw materials (like old car batteries) without pre-treatment. And they can be fired at low temperatures: around 950˚ to 1000˚ Celsius, so in Chinese terms it is a “low-fired” ceramic. Actually the unglazed body usually needs a higher firing first – known as a “biscuit” firing. The pot below shows the white unglazed “biscuit” body at the base.

Sancai jar and lid. H: 8.3cm. China, Tang dynasty. V&A Museum. 

Chemical analysis tells us the elements responsible for sancai colours. The amber-brown comes from iron (2%-5% Fe2O3), green from copper (CuO), and blue from cobalt (with a bit of iron). The straw-coloured glaze is quite similar to the amber but with much less iron (up to 2%). The rare grey-black tones are high in copper (5%+), while brown-black tones are high in iron (8%+). 

I’ve found no evidence on the original sources of these colours. Did a potter go for a stroll one day and notice some odd-coloured soil which he used in an experimental glaze? Anyway, here are a few of my favourite sancai pieces.

Sancai camel and musicians. H: 58cm. China, Tang dynasty, 7-8th C. National Museum of China

This fabulous camel carrying a musical troupe was a funerary offering or ming-qi, buried in the tomb of a wealthy Tang official. Note the musicians’ high-crowned hats, large noses and bushy beards, indicating that they are from Central Asia which was the source of all things fashionable at the time.

Sancai horse and female polo player. H: 35.5cm. China, Tang dynasty. National Palace Museum, Taiwan.

Polo was a popular sport for women in the Tang period, so it's likely that this woman’s right hand once held a polo mallet. Several museums (the Musée Guimet in Paris in particular) have figurines of female polo players on galloping horses but they are mostly painted clay, not glazed like this one. Like the camel-riding musicians, this woman’s head is unglazed. This may be because sancai has a naturally runny effect, which looked artistic on bowls and horses, but rather weird on human faces.

“Egg and spinach” bowl. Diameter: 19cm. China, 17th C, Kangxi period. Bonhams Ltd.

The fascination with sancai continued well after the Tang. The dappled pattern on this 17th C bowl, known as “egg and spinach”, was created in the late Ming or Qing period when potters experimented with archaistic styles. I think it looks like something from the psychedelic 1960s. The brownish-purple (“aubergine”) spots are a particular feature, derived from iron and manganese (not a traditional Tang glaze).

Chinese ceramic glazes - a technical detour

I was going to begin with Tang ceramic glazes but like London public transport, some detours are inevitable on this journey.

Firstly, we can’t study glazes while ignoring the underlying body of the pot, as different pairings give notably different results. Traditionally, Western collectors have divided Chinese ceramic bodies into three categories: earthenware, stoneware and porcelain.

• Earthenware is the oldest, dating back to the early Neolithic age (10,000 – 4,500 BC), possibly earlier. The one below from north-east China is dated around 2,500 BC. Like all ceramics, earthenware is made of clay, whose main chemical components are silicon dioxide (SiO2, known as silica) and aluminium oxide (AL2O3 or alumina). Earthenware is fired in a kiln at around 1000˚ Celsius, which is low by pottery-making standards. Primitive earthenware is unglazed but later versions (like Tang dynasty sancai ware) were glazed.

Earthenware ‘hu’ jar. Majiayao culture, China, 2650-2350 BC. Met Museum NY

• Stoneware is also made of clay but with slightly different levels of silica and alumina, and is fired in a much hotter kiln, around 1,200˚ Celsius. It is a strong heavy ceramic, less porous than earthenware and usually glazed, making it more useful for household pots and jars.

Stoneware storage jar. China, 4th C BC. Minneapolis Institute of Art

• Porcelain, the finest type of ceramic, is made with clay that contains or has been mixed with the mineral kaolin. Oddly, kaolin itself is mostly silicon and aluminium too but it strengthens the clay by a miraculous process called hydrogen bonding, allowing pots to be made thin and light yet strong. Porcelain has a glassy (“vitreous”) translucent quality. It may be fired at very high temperatures, up to 1,400˚C. Chinese porcelain is nearly always glazed, though modern potters sometimes make unglazed pieces to show off the fine underlying quality of their work.

Inevitably, the boundaries between these categories may be blurred, with academics tying themselves in knots to distinguish one from the other. Chinese scholars simply divide ceramics into low-fired or high-fired, and then categorise by style and dynasty (which I suspect is becoming the preferred approach).

Glazed ceramics were invented well before the Tang period: in fact, glazed stoneware was known in the Shang dynasty (1600 - 1050 BC). The yellow-green or grey Shang glazes were made from burnt wood ash. Kerr and Wood believe that once technology allowed kilns to get above 1150˚C, calcium and potassium oxides in the ash reacted with silica and alumina to form an “accidental” glaze when bits of ash fell on to the pots. Eventually, potters collected the ash and mixed it with water to make glaze. But we’ll look at ash and lime glazes in later types of ceramic, so I think we can conveniently skip the Shang. 

We can’t skip the subject of glaze chemistry however, and here again, silicon and aluminium are key players. A glaze is a kind of melted glass overcoat for the pot, so silicon - the main ingredient of glass - is vital. Aluminium oxide makes the glaze viscous and gluey so that it clings to the pot. In addition, a good glaze needs a “flux”. Fluxes are chemicals that encourage the glaze to melt at lower temperatures and become more flexible (“expansive”) so that it fits the body nicely and doesn’t crack. Fluxes are usually something alkaline like potash or sodium oxide, but historically one of the commonest was lead oxide, which we now know is poisonous. As seen in the previous post, lead is still used in some rural areas because it is cheap and extremely efficient.

The fourth key element of glaze is colour, which comes from heating various chemicals in different ways. This too may have been an accidental discovery by potters whose local materials had different chemical compositions. The result is further governed by temperature and levels of oxygen inside the kiln (“kiln atmosphere”). This is where the potter’s art really gets going. Common types of chemical are copper (for red or green), cobalt (blue) and iron (red, brown, yellow, green and sometimes even blue). Titanium dioxide (TiO2) interacts with iron to give a yellowish colour (with high TiO2) or a cool green colour (low TiO2). This will come into focus when we discuss green ceramics or celadons.

Ewer with copper red underglaze. China, 14th C. Early Ming dynasty. Eskenazi Ltd.

In practice, of course, early potters didn’t go around chemical-testing their ingredients. Glazes were made by mixing water or liquid clay with crushed ore or soil from a particular place, according to a recipe handed down by predecessors. An experimental potter might try something different and if successful, would invent a new type of glaze.

But this has provided quite enough to chew on for now, so again like London public transport, this post (intended for the Tang dynasty) terminates here.  

Old car batteries and the Tang Dynasty

Though I try to make these posts entertaining as well as informative, the truth is that this blog is also my scrap-book of useful information. Many times I’ve whipped out my phone to refer to a post: perhaps to show someone the new Famen Temple (cue yelps of disbelief), or to check if Mahendravarman I was the father of Narasimhavarman I (yes he was).

So while visiting a pottery-making village in Myanmar recently, I realised that I needed to put down some accessible facts on the complicated subject of ceramic glazes. This arose because I asked the potter (a nice young woman) what type of glaze she used, and she pointed to a pile of old car batteries.

“No, the glaze,” I repeated foolishly, making paint-slapping movements with my hand.

“Yes,” she said, “we grind up old car batteries to make glaze.” She showed us a bucket of what looked like lumpy black soot.

Because of my hazy recall of glaze technology, it was a while before I realised (with horror) that she was using the lead from recycled batteries. This was why her pieces looked a bit like Tang Dynasty sancai ware which has a lead-based glaze. I will make jolly sure that the little jar I bought (see below) never comes anywhere near food or drink. What happens to the potter families, who all seem to work without protective equipment, is anyone’s guess.

 (Left): Sancai lead-glazed jar (H: 19.5cm), China, Tang Dynasty (8th C). Art Institute of Chicago.
(Right): Lead-glazed jar (H: 10cm). Myanmar, 2019.

I had no excuse for not remembering lead-based glazes, as I’ve studied Chinese ceramics for a while and even wrote an essay on Song dynasty crackled glaze. So the next couple of posts will focus on this somewhat arid but crucial subject. Sorry! Normal service will resume eventually.

Probably the finest authority on this subject is Science and Civilisation in China, Vol V Part 12, by Rose Kerr and Nigel Wood, both masters in the field of Chinese ceramics. But what caught my attention on opening this massive tome was the dedication to Dr Lee Kong Chian, the late Singaporean billionaire and philanthropist. It turns out that Dr Lee and his friend Tan Chin Tuan (another heavyweight of Singaporean economic history) were major sponsors of the Science and Civilisation in China project, begun in the 1950s by the Cambridge academic Joseph Needham. This later grew into the Needham Research Institute which specialises in the history of Chinese science and technology. Kerr and Wood’s treatise on ceramics is only one of over 25 volumes published by the NRI on subjects ranging from mechanical engineering to language structures. The NRI is based in a secluded old house in leafy grounds behind Robinson College, Cambridge, and if I were offered even a cleaning job there, I would take it just to spend my days in such idyllic surroundings.

Meanwhile, I must stick to my aim of writing about ceramic glazes, so first stop: the Tang Dynasty!

The emperor's war-horses keep up the fight

 On a recent visit to the V&A, I was taken aback by this strange clay sculpture of a horse from 3rd or 4th century China. Is that an asparagus growing out of its head?

Source: Victoria & Albert Museum

Anyway, it set me thinking about horses in Chinese art, and in particular those depicted on carved stone panels at the tomb of the emperor Taizong. Looking further into this, I learned something about the panels’ troubled history.

Taizong (r. 626 to 649 AD), the second emperor of the Tang dynasty, is revered in Chinese history as a great ruler: a fearless warrior, highly literate, concerned for the welfare of his people, and open to foreign trade and culture. In many ways, he laid the foundations for the brilliance of the Tang dynasty. The Tang ruling elite were passionate about horses and equestrian sports, including polo which was especially popular among women. They imported top-quality horses from expert breeders in Central Asia whose livestock was superior to the rather weedy local ponies. The Tang love of horses was reflected in their art, notably in the horse figurines which are a must-have for any wealthy Chinese antique collector (see below).

Source: Metropolitan Museum, New York

More importantly, good horses were vital to the army and therefore a symbol of dynastic power and prestige. Taizong led his troops into battle on a series of mighty war-horses which he loved so much that he chose the six greatest ones and had their images engraved on stone panels, each accompanied by a poetic epitaph which he wrote himself. In accordance with his wishes, the huge panels (each measuring 1.6m x 2m) were installed as part of his tomb complex at Zhaoling, 60km north-west of Xian in Shaanxi Province.

Source: University of Pennsylvania Museum of Archaeology and Anthropology

The most famous of the six panels (shown above) depicts the horse named Saluzi, or Autumn Dew. The story goes that while carrying Taizong into battle, Saluzi was hit by an arrow. Taizong’s army chief, General Qiu, pulled the arrow out of Saluzi’s chest then and there, the brave horse showing no sign of pain or suffering. The sculptor (whose identity is unknown) has portrayed Saluzi standing calmly with his legs angled slightly forward, bracing himself, while the general’s knees are bent to show the force needed to extract the arrow.

Each of the six horses was chosen because it carried Taizong to victory at a particularly important battle. All of them sustained serious injuries in the process: for example, the horse named Quan Mao Gua (Curly-haired) was hit by nine arrows but continued to surge forward bravely, as shown in the carving below – the picture isn’t very good but you might just make out two arrows sticking out behind the saddle. 

Source: University of Pennsylvania Museum of Archaeology and Anthropology

A black horse with white socks named Bai Di Wu (White-footed Crow) reportedly carried Taizong on an epic 100km ride through the night. His panel shows him in a “flying gallop”, all four feet off the ground, and his poetic epitaph reads:

With a sword long enough to touch the sky

And this swift steed that could run with the wind

On a gallop I recovered Long

With one look I brought peace to Shu.

倚天長劒, 追風駿足, 聳轡平隴, 囘鞍定蜀.

It turns out, however, that the panels are the subject of a long-running dispute between the University of Pennsylvania Museum, which currently owns the two shown above, and the museum authorities in Xian where the other four remain. According to the UPM’s records, it first received the two panels in 1918 on loan from the Paris-based Chinese art dealer Loo Ching Tsai (known as CT Loo). The museum eventually purchased them from Loo in early 1921 for $125,000. 

It emerged that the panels’ provenance was shady, to say the least. The UPM received a letter in June 1921 from a French collector named Paul Mallon, who thought they might like to know that he had paid a fellow Frenchman named Grosjean to “obtain” the panels from Taizong’s tomb in 1912. Unfortunately, the grave-robbers hired by Grosjean were “attacked by peasants” while carting the loot away. The panels were confiscated by local officials and sent to the district museum. And so poor Monsieur Mallon was left out of pocket, quelle domage. 

The next problem is that no-one knows how the panels ended up in the US. After their sojourn at the district museum, they turned up in Beijing in the possession of the new ruler of post-imperial China, the warlord Yuan Shi-Kai. CT Loo claimed that the shipment to the US was arranged by a local middleman who was authorised by “the supreme authority of the country”, implying that either Yuan, his family or someone in his government had approved the deal, which is perfectly plausible but impossible to verify.

CT Loo himself had a controversial reputation. An orphan who moved to France in 1902 as servant to a Chinese businessman, he became the pre-eminent dealer in ancient Chinese, Indian and South-East Asian art, catering to wealthy collectors and major museums in the US and Europe. Anyone studying the provenance of Asian antiquities in the West will encounter his name repeatedly: an online search of the Smithsonian’s Freer-Sackler collection turns up over 300 hits. As a result, he came to be viewed with suspicion for his links with objects of questionable origin, the Taizong horses being a well-known example. He always denied any wrongdoing, and was in fact known for his philanthropy towards Chinese causes up until his death in 1957.

   

So where does that leave our heroic horses? Demands for their return have been made by authorities in Xian every few years but the UPM is not giving in. Perhaps tellingly, the issue has not come up at the highest diplomatic levels, suggesting that the Chinese central government is not (yet) interested in turning this into an Elgin Marbles situation. Will this change in the new climate of Sino-US relations? The horses probably don’t mind: they’ve seen a lot worse.

Reference material: "Emperor Taizong and his six horses", Zhou Xiuqin, Orientations 32, No 2 (2001); "CT Loo: highs and lows of a great art dealer", presentation by Geraldine Lenain to the Asia Society, Hong Kong (link here)