MUSINGS FROM THE GARDEN OF GREENS AND BLUES: This is the text of an article printed in Ceramics Technical #106 (Ceramics Art+Perception/Ceramics Technical) published by Mansfield Ceramics
As a potter, I find myself conscious of legacy: having an understanding of what has gone before us is not only fascinating but can inform our own practise. In my early potting days I developed a particular fondness for the type of glaze known as Celadon, and was fortunate enough to be able to examine and handle many old Chinese pieces, and use more modern examples. It was the particular qualities of those old glazes that captured me…the soft, luminous sheen, a semi opaque depth created by a myriad of tiny bubbles, the cool hues of blues and greens, and above all, a quietness…
The most plausible view concerning the origins of our use of the term Celadon (in the West) is that it dates back to the arrival of Chinese ceramics into Europe in the mid 17th Century. This period of growing Orientalism saw large consignments of pottery that included green glazed wares, as well as blue-and-white, arriving in Paris. In attempting to describe these new greenwares, writers turned to popular culture. The most well known literary work of the time was a novel by Honore d’Urfe, ‘L’Astree’, first published in 1607. The story was a ‘romantic pastoral’ whose two principal characters were the shepherd and shepherdess, Celadon and L’Astree. As thwarted lovers, their discourses on love and morality were well read, and by the end of the century a commedia dell’arte theatrical production was popular. Celadon strode the stage dressed in a long jade green coloured cape: so, in describing these new ceramics that had appeared, with a colour and depth of glass that resembled green jade, it would have been a simple matter to describe them as ‘green - like Celadon’. Readers would have immediately got the picture. This term has remained with us in the West since, to the point where Chinese archaeologists have accepted and use the term.
The family of glazes known as celadon are a completely natural product, even ‘organic’. It is the predicted end result of a process whereby if you take selected parts of the earth - clays or rocks that contain a small amount of iron - and fire them until they melt, the most common product is a green glass. The celadon produced in northern China were quite fluid glazes, transparent and somewhat olive green in tone, fired in kilns where coal was the fuel: those later produced in the south were more stiff, semi-opaque and with softer hues of blue to green. To achieve this degree and control of melt depended on a sophisticated understanding and control of fire.
Shang Dynasty craftsmen (1500-1050BCE) had mastered the attainment of high temperatures early in their production of bronze wares. The evolution of the ceramic industries was contingent on the ability to build furnaces which could produce significant melting of fairly refractory materials. Current research indicates that proto-porcelains were produced as early as the 1000BCE, using the white clays of North China, which were secondary clays high in kaolin. This would have required firing temperatures up to 1200o C.
Over successive dynasties a wide range of ceramic work was produced, from domestic utility to the terracotta warriors, indicating considerable expertise in kiln construction and operation. As Edmund de Waal outlines in his book ‘The White Road’, makers in Europe in the 18th C struggled to build furnaces capable of achieving temperatures high enough to melt kaolinitic clays to a glassy state: this hindered the production of a true porcelain which could match the greenwares and blue-and-white wares being imported from China.
Recent geological work has proposed that north China and south China were once separate land masses that collided during the Triassic period, when north China struck Siberia some 225-195 million years ago.1 The two mountain ranges that were a product of this collision have given their name to a divide, the Nanshan-Qinling divide, running just north of the Huai river westerly toward Tibet and the Nanshan mountains. This has long been an important geographical, cultural and historical division: geographically, it separates the wheat and millet lands of north China’s Great Central Plain and loess plateau from the mainly rice growing south, and geologically provides quite differing raw materials for the ceramic industry.
Celadon glazes reached their peak productive output in the Sung dynasty in China, a period which lasted nearly 300 years, from 960-1267. Initially the capital of the Empire was based in Kaifeng (Northern Sung) until it was overrun by the Mongols, whence the capital moved to Hangzhou, in south eastern China (Southern Sung). The geographical shift is of great importance in the evolution of greenware glazes, as it brings into play the significantly differing geologies of the north and south. Northern stoneware and porcelain clays tend to be more kaolinitic, being higher in alumina and lower in silica than their southern counterparts. Southern materials also tend to be richer in alkaline fluxes, particularly potassium oxide from their high content of secondary hydro-micas.
Ash glazed precedents
Early pots produced in southern China were primarily made for ritual uses, and ceremonial burial, in a gradual replacement of bronze. These ceramics could be considered to be stonewares, using a low-iron clay fired in reduction to temperatures approaching 1200o C. The kilns were fired with wood, and at these temperatures wood ash has a natural glaze effect: it is only a small step from here to the deliberate application of dry wood ash by sprinkling, and another short step to developing a solution of wood ash and clay that could be dipped or sprayed. The employment of calcareous ashes (ashes high in calcium, or lime) was an approach that created compositions in the region of the silica-alumina-calcia-magnesia eutectic mixture, allowing a reasonably fluid glass surface as temperatures rose toward 1200o. A glaze mixture of ash and low-iron siliceous clay, fired in reduction, would naturally give a greenish glass. In reproduction, a balance of about 3 parts clay to 2 parts washed ash provides the best fit for most cases of these early glazes.
These glaze compositions are simple to prepare. Clay and ash will remain in suspension, so refined glazes could easily be prepared through levigation (washing, allowing the more solid elements to settle, and drawing off the fine material held in suspension). They were tolerant of temperature variations in the kilns, and at the higher end their transparency was conducive to lightly carved or incised decoration. Southern kilns were of the many-chambered dragon type: temperature rise to finishing was quite fast through side-stoking, with an approximate end of around 1220o C.
It is clear from the historical records that in burning botanical fuel to create wood ash, large amounts of shrubs and trees were cleared to provide sufficient washed ash for the widespread production of greenwares and other glazes. It has been estimated that as little as 1/250th. (0.4%) of the weight of the original fuel would survive as prepared ash for glaze making. This continual depletion of resources may have led to the adoption of limestone as an important glaze flux in southern Chinese kilns in the 10th to 11th centuries, and been responsible for the significant change in composition from a high lime glaze (using ash) to a lime-alkali formulation. This would have given the glazes a broader firing range and an improvement in glaze quality.
By the Tang Dynasty (618-906), greenwares had become more refined and were more widely accepted, but they were in competition with the growing popularity of high-fired whitewares – in effect, the first true porcelains. Tang porcelain, which includes Ding and Xing ware (Ding ware fired in oxidation, Xing in reduction), were made in kiln areas north of the Qinling divide using kaolinitic clays that were fired to high temperatures in the ‘mantou’ type kilns, with coal as the fuel. The following dynasty, known as Northern Sung (960-1127), with the capital based in Kaifeng, produced fine celadon glazes that were typically fluid, transparent and tending toward an olive green colour. Although these pots were a high quality ceramic, they were not as well favoured as the whitewares by the ruling court.
As dynastic changes forced the removal of the ruling Empire to southern China, cities such as Jingdezhen became the centre of production of white-fired ceramics. This move showcased the quite different geology of the southern raw materials, and allowed the development of bodies that often contained very little clay. Potters used a high-mica ‘porcelain stone’, known as baitunze, which has a low degree of plasticity. In the early southern whiteware, known as Qingbai or Yingqing (shadow-blue), the body was a combination of porcelain stone and a smaller amount of white clay: the glaze was then made from a mixture of the body material and limestone, probably in a ratio around 70/30. Recent analysis of materials and shards from kiln excavations in the Jingdezhen area indicate that some of the kilns may have further refined their processes to the point of using separate porcelain stones for body preparation and for glaze material. Baitunze stone is plastic and moderately fusible, and contains a high level of sericite, a potash mica. This was used as a body stone. A similar stone known as youguo, from Sanbaopeng (near Jingdezhen) is a high albite material (soda mica), and is more fusible and only moderately plastic. Bodies appear to have been made of baitunze and approximately 30% kaolin, and glazes of youguo and approximately 30% glaze-ash (limestone).
In the evolution of ceramic practice, it seems these two factors contributed to the growth of the type of blue/green glazes we know as celadon: the use of limestone as a glaze flux, and the use of a porcelain stone/clay mix for both bodies and glazes. In Zhejiang province, where celadon production reached its peak, the porcelain stone had a slightly higher iron content than further west, Jiangxi, the centre of whitewares. Glazes of a jade green tone (also called plum green, or kingfisher green) were a feature of the Longquan kilns, which appear to have used a glaze mixture of a sericitic porcelain stone with some red clay. The kilns of Dayao, some 30kms away, used a local porcelain stone mixed with a low-iron clay, and their glazes are more known for their distinctly blue tones.
A contemporary description of the process of firing celadon, still called ‘greenware’, or qingci by the Chinese, is contained in writing by Lu Jung from c.1475, the ‘Shu Yuan Ca Ji’, Miscellaneous Notes from the Garden of Beans and Peas…2
Green high-fired ware came first from Liutian…the clay dug from other areas was not as good as that from near the kilns. The glaze was composed with wood and leaf ash mixed with very fine limestone dust from the hills. Craftsmen first formed vessels on the wheel, or in moulds, then allowed the clay to dry, following which they glazed them, placed them in saggars which they positioned carefully in stacks in the kiln. The wood fuel burned night and day, and the fire door was closed and sealed when the fire was red hot and without smoke. The firing was finished when the fire had completely burned down.
The output of potters over the last two thousand or more years has largely been dependent on processing local raw materials. In the modern era, as ceramic suppliers become more international conglomerates, our materials are less likely to have a local origin. Clay makers use clays that come from England, France, Malaysia, China, as well as local Australian clays. Our glaze materials similarly have a global origin, as have the materials for stains and colours. We now have the luxury of being able to select refined materials of unspecified origin. If we can avoid this, and seek an opportunity to harness some material that is local, we potentially gain an element which can define our work as our own, or allow it to have an identity of place. We can add an intangible, the ‘known unknown’ of that material, which may bring a unique character to the finished work and provide a sense of connection.
In my own stoneware and porcelain, I am attempting to reproduce some of the character and quality found in the best of older Chinese celadon, making modern tableware which is strong and enduring with glazes that have depth and luminosity. I live and work in the Blue Mountains, which, being all sandstone, has limited materials useful for potters. I prospect for my materials in the Tablelands of NSW, west of the mountains. The largest clayfields in NSW are in the Mudgee-Gulgong area, and I use some clays from there to make a stoneware body for celadon. My studio is too small to store materials and machinery that would allow me to completely make my own clay bodies, so I am reliant on some commercially made bodies. My particular focus is on glazes, and glaze quality, and this is where I seek out raw materials that can make a contribution.
I have made many celadon glazes, with two currently in use: a ‘blue’ celadon using a schist from a hillside called Blue Biddy, just outside Gulgong on the Guntawang road, and a green celadon which uses a shale-like material from near Lue, on the road from Rylstone to Mudgee. The initial formulation for the glazes was based on analysis of historical examples published by numerous Chinese and western researchers, many of which have now been collated in Science & Civilisation in China vol. 12 by Rose Kerr and Nigel Wood.
I started with Australian clays and rocks whose chemical analyses were known, published in Ivan McMeekins’ book, “Notes for Potters in Australia”. Over the years, as I have found and experimented with other materials, I have only needed to adjust recipes, depending on the colours and qualities these new materials of unknown analysis gave me.
My blue celadon is related to the celadon from Dayao, based on a sericitic porcelain stone. The Blue Biddy schist is no porcelain stone, but is a soft, metamorphosed clay based material that does contain a significant amount of sericite mica. My green celadon is a more commonly recognized jade green type, related to the Longquan glazes which were slightly more fusible. The Lue shale in this glaze has a higher iron content and very little mica. The final composition uses the clay body as the clay fraction in the glaze, and is ball milled for several hours to finely grind all the ingredients. My celadons have a higher than usual clay content for glaze that is applied to biscuit ware, as this helps keep the Alumina/Silica ratio closer to 1:7.5, giving the glazes a broader firing range - the glazes have a soft, buttery opacity and sheen around 1260o, becoming more transparent as temperatures approach 1300o.
My interest in using raw, or found materials, is not new or unique. Many potters choose to work in this way, as it helps provide a cherished connectivity to their local landscape. The words of the scholar Zhao Kai, known colloquially as the Porcelain God, were written in the 7th century, and still remain apt.3
Knowing the secret ways of the winds and the rains, he penetrated deep among the slumbering rocks and learned their histories. He took the rocks and pounded them; using subtle mixtures, he formed the vessels and works of beauty from loaves of plastic clay. With precision he learned to blow upon the flames and transmuted his fragments of hillside into fragile bowls for the delight and use of man.
My ongoing academic and practical fascination with the glaze family celadon stems from that quiet beauty which they bring to the table: however, it is the intimate connection to the landscape made through finding, processing and transforming local clays, rocks and ashes into vessels that may make a contribution to the pleasure of our lives which is my inspiration.
1 Joseph Needham, Science & Civilisation in China, Vol. 5 Part 12 Ceramic Technology, by Rose Kerr and Nigel Wood pp. 49-51
2 Ibid. pp. 578-579
3 A D Brankston, Early Ming Wares of Chingtechen, 1938 p.61