Porcelain and Bone China E-Book

Sasha Wardell

• Herausgeber: Crowood
• Kategorie: Lebensstil
• Sprache: Englisch

Veröffentlichungsjahr: 2020

Beschreibung

Porcelain and bone china have fascinated patrons, collectors and makers for centuries. This practical book looks at their composition, making methods and decorative techniques, as well as glazes and firing processes. It examines their different characteristics and explains how designers have worked with these clays within the ceramic industry. This new edition includes an additional chapter that introduces emerging technologies and new materials. It is a beautiful book that gives an authoritative account of these enduring materials, which ceramicists enjoy so passionately. It includes over 250 colour illustrations of instructional photos and inspiring finished pieces.

Leseprobe

PorcelainandBone China

PorcelainandBone China

Sasha Wardell

SECOND EDITION

First published in 2004 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

www.crowood.com

This e-book first published in 2020

Revised edition 2020

© Sasha Wardell 2004 and 2020

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 1 78500 680 7

Acknowledgements

First of all, I would like to thank all the ceramicists who have so readily contributed and whose work features in this book. In particular, I would like to extend further thanks to the following people whose contribution has been invaluable in the sourcing and preparation of this book: Angela Mellor and Sandra Black in Australia; François Ruegg and Wolfgang Vegas in Switzerland; Pascale Nobécourt in France; Hubert Kittel and Karin Bablok in Germany; Adrienne Kriel in South Africa; and Sue Pryke, Kathryn Hearn and Tavs Jørgensen in the UK, as well as Keeley Traae at Wedgwood and Nadia Demetriou Ladas at Vessel in London; Hélène Huret, Director of the Bernardaud Foundation, Limoges, France; Michael Eden, ceramicist and curator of the Sans les Mains exhibition at the Bernardaud Foundation; David Slinn, Global Ceramic Materials, Stoke on Trent.

I would also like to mention the assistance offered by the CPA Charitable Trust, the British Museum and the Museum of East Asian Art, Bath, for which I am most grateful. The technical advice given by Alan Ault of Valentine’s Clay Products and John Liddle from Ceram Research was invaluable, and thanks must also go Mary Clark and Peter Scott for their painstaking proofreading and to Charlie for his computer advice.

Contents

Introduction – ‘White Gold’

1Composition of Porcelain and Bone China with Recipes2Making Methods – Throwing3Making Methods – Hand Building4Making Methods – Slip Casting5Decorating Techniques – From Raw to Onglaze6Glazes and Firing Processes7Designers/Makers Working Within the Ceramic Industry (Introduction by Sue Pryke)8Advanced Technology9Emerging Technologies and New Materials

Appendix

Glossary

Bibliography and Further Reading

Suppliers

Index

Introduction

‘White Gold’

This introduction aims to give a brief overview of the history of the origins of porcelain and bone china, particularly with reference to the economic and social developments of the ceramic industry of the UK and continental Europe.

Porcelain

It is not possible to give an exact date for the discovery of porcelain, as its creation was a long, slow evolution that took place over several millennia. China, with its naturally occurring kaolin deposits and already skilled potters, presented the ideal combination for the beginnings of porcelain manufacture.

At that time, the Chinese empire stretched from Mongolia in the north to Vietnam in the south, and its population was subject over time to a wide variety of monarchs and regimes. It is believed that the first porcelain was made during either the Sui (AD 581–617) or early T’ang (AD 618–906) dynasties and was of an appearance which we today would liken to a high-fired white stoneware.

The Liao dynasty (AD 907–1125) produced what was termed a ‘porcellanous’ body, which was close-grained and white with a distinctive creamy glaze, whilst the Song dynasty (AD 1128–1279) produced some fine, varied and classically simple porcelain wares, which were predominantly flower-inspired. Taking the form of lotus bowls and vases, they were minimally decorated apart from subtle surface carving and pale green celadon glazes.

A melon-shaped ewer has been found in a tomb dated AD 1099. The long spout is typical of the period, while the blue tinge of the piece is indicative of early eleventh-century ware. In the first half of that century such blue was occasionally produced by accident; however, by the late eleventh century, this effect was actively sought.

Blue and white meiping vase decorated in the ‘windswept’ style. Ming dynasty, second half of the fifteenth century. (Permission of the Museum of East Asian Art, Bath)

Qingbai melon-shaped ewer.Northern Song dynasty. (Permission of the Museum of East Asian Art, Bath)

Qingbai meiping vase with carved peonies. Yuan dynasty, late thirteenth century to early fourteenth century. (Permission of the Museum of East Asian Art, Bath)

Following this period, the Mongols came to power and formed the Yuan dynasty (AD 1280–1368). Porcelain manufacture started to become grander and more complex, due to the improvements in technology and clay composition. However, weak monarchs, disorderly administration and general poverty coupled with natural disasters, such as droughts and floods, all contributed to the decline and collapse of this relatively short-lived dynasty.

The meiping vase shown here has a body decorated with a broad band of carved peony scrolls with incised details delineating the leaves, bordered by overlapping swirling petals on the upper part and tall lotus petals around the lower half. The vase is covered with a glossy bluish Qingbai glaze. The decoration is similar to that found on Longquan celadon wares of the Yuan dynasty. This type of decoration, whilst typical of celadon of the Yuan period, is rarely seen on Qingbai pieces. It has been suggested that it was probably produced at one of the celadon kilns of Zhejiang province rather than in Jingdezhen, a town that was significant in the production of porcelain.

Following the Yuan dynasty, the Ming dynasty (AD 1368– 1644) spanned a period of some 300 years of peace and prosperity. Seventeen autocratic emperors ruled over China’s transformation from an agriculturally based society to a more industrialized one. Profound social changes took place, which led to the development of a cash economy, technical advances, huge growth in cities, the spread of literacy and the industrialization of handicrafts.

It was during the Yuan and Ming dynasties that Jingdezhen became particularly significant in the production of porcelain. This town, in the southern province of Jiangxi, developed as the most important centre for porcelain manufacture due to its geographical position. Being well-situated on a system of inland waterways, and close to raw material deposits, it was an ideal choice for a manufacturing centre, especially as, with dwindling agricultural work, there was also a ready made workforce available for employment. Advances in technology went on to pave the way for more sophisticated and colourful porcelains, moving away from the previously popular celadons.

Porcelain was used throughout Chinese society, ranging from small-scale family use to the royal households, with decoration depicting five central themes: historical, technological, trade, religious and social. A variety of imagery and iconography was used on the ware, including cranes and peaches symbolizing long life, as well as hobby-horses, which were a metaphor for scholarly success.

The discovery of pottery and porcelain artefacts in burial graves has greatly assisted our understanding of these materials. Following the Buddhist belief of ‘life after death’, people were buried with bolts of cloth, gold ingots for currency, as well as entire miniature porcelain crockery sets, fully equipping them for the life hereafter.

Although Chinese celadon porcelains had been sent to the West centuries before, it was during the Ming era that the first large parcel shipments of ‘blue and white’ were exported to Europe (Portugal), America (New Mexico) and Africa (Malindi), fuelling interest and intrigue regarding this precious commodity. It was in fact the Europeans who coined the name ‘porcelain’ deriving it from the Portuguese word ‘porcellaneous’ meaning ‘shell-like’. There was direct trade between Europe and China after the successful achievements of maritime exploration. In 1517 Vasco da Gama returned to Portugal from one voyage with porcelain and pepper for King Manuel I.

After dominating these trade routes in the early 1500s, the Portuguese were superseded by the Dutch. This followed the closure of the port of Lisbon by Philip II of Spain during the war between Spain and Portugal. However, by then Chinese porcelain had reached nobility in other parts of Europe, including Henry VIII in Britain and Francesco I de’ Medici in Italy. The latter resulted in the earliest recorded attempts to recreate Chinese porcelain in his court laboratories in Florence in the 1570s.

Korea was the next country after China to produce porcelain, and a thriving industry developed. However, the Koreans suffered defeat at the hands of the Japanese in 1592 and the industry collapsed. A Korean potter was taken to Japan as a prisoner, in the hope that he would divulge his knowledge to the Japanese. He discovered a fine porcelain stone in the mountain of Izumiyama in the Arita region and production began. Being close to the port of Imari, from which it got its name, this famous Japanese porcelain was subsequently shipped all over the world. Although the Japanese gleaned their porcelain-making skills from the Chinese and Koreans, a typical Japanese style developed with the Arita potter, Sakaida Kakiemon, whose famous onglaze decoration was later imitated by the Worcester, Derby and Meissen factories in the eighteenth century.

The introduction of porcelain to Europe, by way of shipments via the English and Dutch East India Companies, provoked an enormous interest and quest to find the arcanum (recipe) for this precious material. During the 1600s, there had been several unsuccessful attempts to simulate porcelain which had, by then, become as important a commodity as gold, or ‘white gold’ as it came to be known. It was common practice for northern European monarchs to create a ‘porcelain room’ where huge collections were on show.

After the experiments in the Medici porcelain factory in Florence in the 1570s, there was quite a period of time before other countries such as Holland, Switzerland, Denmark, Sweden and Russia conducted experiments. However, Germany and France were to become the main players. In Germany, events were unfolding that would lead to the invention of ‘true’ or hard-paste porcelain. This colourful and compelling story is superbly described in Janet Gleeson’s book The Arcanum. However, to put it into some form of historical context, the main events are chronicled as follows.

Stem bowl decorated in underglaze blue and Langyao red.Qing dynasty, Yongzheng mark and period (1723–35). (Permission of the Museum of East Asian Art, Bath)

An alchemist named Johann Freidrich Böttger (1682– 1719) was taken prisoner by Augustus of Saxony, King of Poland. Böttger proclaimed that he could make gold and, latterly, porcelain – a rash claim. However, in 1708, after five years’ imprisonment, and with the assistance of scientist Pabst von Ohain and, subsequently, mineralogist Ehrenfried Walther von Tschirnhausen (1651–1708), Böttger was able to produce some early experimental pieces. The resultant ware using clay and alabaster (later substituted with feldspar) was the key to the breakthrough they had been working for – a white and translucent porcelain that held its shape. Coupled with the discovery of some kaolin deposits at Colditz, Böttger was well on the way to reproducing the highly acclaimed hard-paste porcelain of the Orient. Unfortunately, von Tschirnhausen died the same year as the breakthrough, which meant he did not live to see the results of his combined efforts and Böttger had lost his main ally and confidant.

In 1710 the Meissen factory was established under the patronage of Augustus of Saxony, with Böttger being appointed the factory’s administrator. However, following his death in 1719, at the age of 37, the factory was found to be in huge financial debt. Much of the subsequent developments have been credited to Johann Gregor Herold (1696– 1775), an Austrian painter and colour chemist, who had joined the factory in 1720, and to Johann Joachim Kändler (1706–75) in 1730, a gifted modeller who set the precedent for the famous Meissen figures.

In France, the perfection of artificial porcelain, known as pâte tendre or soft-paste porcelain, was first credited to the Poterat family at Rouen c.1673. The characteristics of this material were a lack of translucency and a ‘softness’ which meant that the glaze could easily scratch.

At that time, there were four significant producers located in and around Paris.

In 1678 at St Cloud a soft-paste porcelain was developed, although official production only started in 1702 when the patent was granted. Influenced by the Imari, famille vert and Kakiemon ware, this porcelain had the appearance of a creamy or ivory tone, with a soft and shiny surface indicating that a glassy frit was used as a flux, instead of feldspar.

Production then began at Chantilly in 1726, and the town became famous for its Kakiemon-inspired ware and distinctive opaque tin glaze. Later, production commenced at Villeroy, with an early ware that was similar to St Cloud and included rococo-style pot-pourris. Finally, a factory opened at Vincennes in 1740. This latter factory was an important landmark in the production of porcelain for, having been granted a royal warrant for the exclusive rights of manufacture of ‘porcelain in the style of Saxony’, it was able to produce richly decorated ware with flower and bird motifs using gold. However, Vincennes still had to be content with producing the soft-paste body, as kaolin was not discovered in France until 1768. In 1756, the Vincennes factory moved to Sèvres, becoming the most important manufacturer in France thanks to its technical expertise and variety of colour and decorating techniques.

During this period, the all-important discovery of kaolin in 1768 at St Yrieix in the Limousin occurred. This meant that hard-paste porcelain could, at last, be produced, leading to the development of new and extended colour ranges and techniques, in particular enamel on gold foil. The two pastes or clays were simultaneously produced up until 1804, when soft paste was abandoned in favour of hard paste.

In the midst of all this production around the capital, the town of Limoges became synonymous with porcelain, as it still is today, not only because of its proximity to the newly found kaolin deposits, but also thanks to a few entrepreneurial businessmen who capitalized on this discovery by mining and exporting kaolin all over Europe. They subsequently opened up porcelain factories where highly skilled craftsmen collaborated with well-known artists to produce some of the finest examples of European porcelain.

Bone China

During this time, England had been pursuing its own experiments. Triggered by the increasing popularity of tea drinking, porcelain was in great demand, so, by the 1740s, factories in Staffordshire, London and Bristol had embarked on the familiar quest. Prior to 1780, however, English porcelain was likened to the early soft-paste French bodies where a glassy frit was added and firings were carried out to 1100°C. This differed from the hard-paste porcelains found in Germany and later in France, where the firing temperatures reached 1400°C.

Although a relatively successful attempt to create ‘true’, or hard-paste, porcelain was made at Plymouth in 1768, these fritted wares were difficult to work with, particularly when used in conjunction with the unplastic nature of the English china clays. The successful manufacture of porcelain, therefore, was seriously inhibited until the introduction of bone ash, which lessened the risk of collapse during firing. By 1747 inclusions of this versatile material had been undertaken in factories at Bow in London and Lowestoft with some success. However, it was not until 1749, when Thomas Frye of the Bow works patented, for a second time, the use of bone ash, that any headway was made into the development of a relatively high-fired white clay or ‘china’. Frits, however, were still included in the body at that time.

This remained the case until finally, in 1794, Josiah Spode of Stoke-on-Trent initiated the change to the present mixture of bone ash, Cornish stone and china clay. This English hybrid between soft- and hard-paste porcelain was originally termed ‘Stoke China’, later becoming known as bone china. Having dispensed with the use of frits entirely, this resulted in a body that eventually became the basis of today’s bone china. Stoke-on-Trent became synonymous with bone china production, remaining so to this day.

Even in the present economic climate, factories such as Worcester, Derby and Wedgwood, which have their origins in the mid-eighteenth century, still exist and continue to produce both classical and innovative products, albeit for what appears to be a dwindling market. However, a new generation of small, independent factories has sprung up to cater for the ever-changing needs of today’s consumer (seeChapter 7).

An illustration taken from a series of twenty-four nineteenth-century album illustrations showing the manufacturing process of porcelain. Ink and colours on paper. (British Museum – given by Miss W. M. Giles)

‘Forest Floor’ by Les Blakebrough. (22cm diam. × 18cm h.) Thrown Southern Ice porcelain with water erosion technique. Unglazed. Reduction-fired to 1300°C. 2001. (Photo: Uffa Schultz)

1

Composition of Porcelain and Bone China with Recipes

Although porcelain and bone china are sometimes erroneously classed as one and the same material, there are some fundamental differences that distinguish them from each other both historically (see Introduction) and technically. Whilst they share some raw materials and characteristics in common, their differing ingredients, recipes, shrinkage rates and firing treatments serve both to highlight and contribute to their individual qualities.

Both possess ‘whiteness’, translucency and strength, to a lesser or greater degree, as well as being high-fired and vitrified when mature. However, there are some subtle differences concerning their properties: porcelain tends to be ‘warmer’, with tones of white ranging from creamy off-white (in oxidizing firings) through to bluish-white (in reduction firings). Bone china, on the other hand, tends to be ice-white, or ‘cold’ in colour, unless it has been under-fired, whereupon it takes on a pinkish hue. Some say that the colour of the body determines how translucent the clay appears, even when both have been fired to their maturing temperatures.

Porcelain is generally stronger in its ‘green’, or raw, state, allowing for certain decorating techniques such as piercing at the leather-hard stage. Bone china, however, requires a soft firing to 1000°C before the ware can be safely handled (seeChapter 5). The fired strength of these materials is determined by their respective high-firing temperatures, with hard-paste porcelain being particularly strong.

The following recipes highlight the differences between the two materials. The recipes are supplied courtesy of Alan Ault of Valentine’s Clay Products in Stoke-on-Trent (see Suppliers).

Basic Recipes for Porcelain and Bone China

A basic porcelain recipe is as follows:

50%

china clay

25%

feldspar

25%

quartz

2–3%

ball clay/bentonite.

Standard low biscuit firing: 1000°C.

Standard glaze firing: 1280–1450°C*

*(hard-paste porcelain).

Shrinkage after firing: 12–15% (depending on the firing).

Bone China

A basic bone china recipe is as follows:

50%

bone ash

25%

china clay

25%

Cornish stone*

1%

ball clay.

* A type of feldspar now replaced by a more stable Italian feldspar.

Standard high biscuit firing: 1250°C + 1hr 30min soak.

Standard glaze firing: 1020–1080°C.

Shrinkage after firing: 10–12% (depending on the firing).

Average length of biscuit firing cycle: twenty-four hours, including cooling.

When looking at these basic recipes, the two main differences in the ingredients become clear: porcelain contains quartz and no bone ash, whilst the reverse is true for bone china. The fact that there is no quartz present in bone china means that it can be fired straight up to its top temperature in two hours, without any of the concerns normally associated with quartz inversion (see Glossary). Although the ceramic industry has kilns that are capable of fast-firing, it is not recommended for the individual ceramicist, as this will quickly damage the elements of a studio kiln.

The bone ash that makes up half of a bone china recipe is a by-product derived from cattle bones that were originally imported from Argentina, Holland and Sweden. As animal bones are used in the glue industry, once they have been boiled for manufacture, the residue is calcined and ground, then introduced into the china body. (Crown Derby Bone China manufacturers use ox bone ash from a Dutch glue factory.) By-products feature quite prominently in the china industry, as bone china biscuit seconds are used as ‘landfill’ underneath Tarmac roadways!

Raw Materials

The analysis of raw materials can be obtained from suppliers.

China Clay (Kaolin)

(AL2O3 2SiO2 2H2O)

The name kaolin is derived from the Chinese word kao-ling, which refers to the ‘high mountains’ in which the deposits of the original clay were found. China clay is a primary clay, meaning it is closely associated with the parent rock, and is obtained by washing the rock using high-pressure hoses with the slurry being collected in settling troughs. It is found in large quantities in Cornwall (UK), Florida and Carolina (USA), Tasmania, New Zealand and other areas of Western and Central Europe.

It is a very white clay with a large particle size. This results in poor plasticity, or workability, and generally means that other ingredients are required to make it a viable material. Chinese kaolin is the most plastic, with Cornish china clay being the least.

China clays have a high alumina content and can contain very small amounts of titanium and iron oxides, which will ultimately affect the colour of the body – the lower the quantities, the whiter the body. Grolleg and Standard Porcelain China Clay from Imerys in Cornwall (see Suppliers) are amongst the whitest firing, along with Edgar Plastic Kaolin (EPK) from the USA and Tonganah kaolin from Tasmania (see Southern Ice porcelain recipe p. 15).

Feldspar (Potash Feldspar)

(K2O AL2O3 6SiO2)

Feldspars come from a large group of minerals that have decomposed from granite and igneous rocks. They consist of the alumino-silicates of potassium, sodium and calcium. The most commonly used in high-firing clays is potash feldspar, which is pinkish in colour and acts as a primary flux (that is, has the effect of lowering the melting point of silica) in porcelain bodies. Large amounts will increase translucency, as well as the possibility of distortion, whereas smaller amounts will raise the maturing temperature but reduce translucency.

Quartz

(SiO2)

This is almost pure silica occurring as rock crystals or as silica sand. Loch Aline on the west coast of Scotland is the main source for silica sand in the UK. Flint can also be used, but it is not as pure as quartz. Quartz is the glass-former in a porcelain body, rendering it hard and durable. It has a very high melting point of 1710°C, therefore must be used in conjunction with a flux. Quartz is finely ground and available in ‘mesh’ sizes, for example 300s mesh; the higher the mesh number, the smaller the particle size. If too much quartz is present, the porcelain may crack, whereas too little may lead to crazing problems in glazes.

The quartz is normally ‘leached’, a process whereby the iron is removed, resulting in as pure a material as possible.

Ball Clay

The name ‘ball clay’ derives from the 30lb balls in which this clay was originally formed for transportation by horse and cart. These are secondary, or transported, clay deposits, produced by the weathering and erosion of granite rocks, which are broken down and carried by streams.

Ball clay has a very fine particle size, therefore it is very plastic in nature, with a high shrinkage rate. It can cause discolouration if used in large amounts; however, small quantities of 1–3% will improve plasticity and strength in both porcelain and bone china bodies.

Bentonite

Bentonite is also a secondary clay. It can be used as a substitute for ball clay as it also has an extremely fine particle size.

The differing properties of these raw materials, whilst nonviable when they stand alone, form the basis of arguably the most seductive of high-firing clays when they are combined.

It is now possible to buy a range of ready made porcelain and bone china bodies from reputable manufacturers worldwide (see Suppliers), including the French Limoges porcelain, which is designed to fire to 1400°C and is a favourite amongst many ceramicists.

Ready-Made Porcelain Clays for Individual Makers

An increasing number of ready made clays have been created to meet the needs of individual makers. Notable examples of these in the UK are David Leach porcelain (Potclays), which was developed by him in the 1970s, and Audrey Blackman porcelain (Valentine’s Clay Products). Southern Ice porcelain (Walker Clay Co.) features strongly in Australia.

The basic recipe for the David Leach porcelain is as follows:

52%

standard porcelain china clay

25%

potash feldspar

20%

quartz 200

3%

Quest white bentonite.

Anne James (UK) (seeChapter 6) uses this as the basis for her raku body:

52%

standard porcelain china clay (powder or Grolleg)

25%

FFF feldspar

18%

quartz 200

5%

bentonite.

She makes a slurry and sieves this recipe twice (80s and 120s meshes) before adding 10% molochite (refractory grog) to it.

Audrey Blackman (UK) porcelain is another body which was specifically developed for a particular need – namely modelling and throwing. Due to the high plasticity of this body, it is not suitable for casting and is only available in pugged or plastic form. It has a firing range of 1220–1280°C. Both Margaret O’Rorke (UK) and Gilda Westermann (Germany/UK) use this porcelain body for certain aspects of their work.

Karen Downing (USA/UK) uses a 50/50 blend of Valentine’s Audrey Blackman and Special porcelain for her thrown work. She says:

After experimenting with a number of porcelain bodies, I settled on the Audrey Blackman because of its whiteness and responsiveness in throwing. However, problems with spiral cracking in drying make it untenable to continue using on its own. I now mix the two bodies in a de-airing pug mill and seem to have resolved the spiral cracking without compromising the qualities which initially drew me to the Audrey Blackman. The pots are then fired in an electric kiln to cone 8 (1260°C).

Les Blakebrough (Australia) has produced a porcelain clay with particularly white, translucent qualities (see the Chapter opening illustration). Southern Ice porcelain derives its name from the area where it was generated – Hobart, Tasmania, which is one of the southernmost parts of the Southern Hemisphere. It was developed over a period of six years by a small team of associates with support from the Australian Research Council and the University of Tasmania. Since its commercial release by Clayworks of Dandenong, Victoria, the clay is now being exported to several countries including the UK and USA.

One of the issues that drove this research was the fact that Blakebrough wanted a clay that would stand up to scrutiny even if it remained unglazed. Being dissatisfied with what was currently available, he embarked on the Southern Ice project, attempting to use the local raw materials. Kaolin deposits found at Tonganah, near Scottsdale, were already being used in a paper manufacturing plant and proved to be suitable. However, high-quality feldspar, silica and bentonite were not available locally, so it was necessary to turn to commercially produced materials for the rest of the recipe.

Therefore, after a series of tests involving slight alterations in the major body constituents of kaolin, feldspar and silica with the addition, or deletion, of auxiliary fluxes, the following recipe seemed the most favourable:

50%

Tonganah kaolin

30%

potash feldspar

20%

silica 300

5%

bentonite H.

(For further information on this research refer to Ceramics Technical, No.1, 1995, and Ceramic Art and Perception, Vol. 24, 1996.)

Stack of straight-sided porcelain dishes by Karen Downing. 2002. (Photo: Mark Somerville)

‘Whites’ by Juliet Armstrong. Slip cast, pierced and polished bone china.

‘Waterfall’ series by Angela Mellor. (18cm h.) Slip cast bone china with paperclay inlay. Fired to 1250°C. 2002. (Photo: Victor France)

A few UK makers have adopted this clay, reinforcing its popularity. Amongst them are Joanna Howells (see Chapter 2) and Peter Lane (seeChapter 5).

Bone china has the reputation of being notoriously difficult to make up in a studio situation, so makers generally rely on the commercial manufacturers to do the hard work (this is certainly true in my case!). However, being a particularly ‘English’ material, very few makers outside of the UK are willing to pay the high cost of importing what is already an expensive material. Nevertheless, this has not deterred South African ceramicists Martha Zettler (seeChapter 5) and Juliet Armstrong.

Armstrong has persevered in producing her own bone china body. However, she has experienced a high failure rate – with whiteness and translucency being her prime objectives, this has meant that the body has been pushed to the top of its vitrification range.

Her recipe is as follows:

50%

bone ash (using a chemical substitute tricalcium phosphate)

25%

SS porcelain (imported from UK)

25%

Blesberg feldspar (from South Africa).

Firing temperature: 1260°C with a one-hour soak.

Ceramicists working in bone china on the other side of the world have experienced the same type of problems. Both Sandra Black (seeChapter 5) and Angela Mellor use a recipe which was developed by Dr Owen Rye in Australia:

30%

Eckalite No.1 kaolin

45%

bone ash – natural

22.8%

potash feldspar

2.2%

silica.

To make this plastic body into a casting slip add:

2g

Dispex* per kg of dry weight

1g

sodium silicate

600ml

water per kg of dry weight.

* See Glossary

In the recent past, paperclay, used in combination with both porcelain and bone china, has resulted in some fine examples of heightened translucency. Anne Lightwood is a UK maker who has carried out extensive research into this area. Her book, Working with Paperclay (The Crowood Press), is an excellent source of reference on this subject. The porcelain recipe she uses, in conjunction with the paperclay, originated from Donald Logie (Duncan of Jordanstone College in Dundee):

45%

Grolleg china clay

20%

Hyplas 71 ball clay

20%

feldspar

15%

quartz

2%

bentonite

2–5%

molochite.

When in slip form, she adds one part soaked cellulose pulp to two parts slip.

Others who include paperclay are Frances Priest (UK) using it with bone china (seeChapter 3) and Maggie Barnes (UK) with porcelain. Barnes makes her porcelain paperclay from equal parts of Southern Ice porcelain and 100% cottonfibre pulp. The slip should be the consistency of thick cream and the prepared pulp should have as much surface water as is feasible. The mixture is well-beaten in a glaze-mixer, then poured onto plaster bats to remove surplus moisture. The resultant sheets are rolled thin for translucent work, or laminated together to create thicker slabs for tiles and panels.

Detail of ‘Reptile’ panel by Maggie Barnes. Porcelain paperclay with pure porcelain stained slip decoration. Unglazed and polished. Fired to 1260°C. 2002. This piece was created during a research and development project sponsored by Yorkshire Arts. (Photo: Jerry Hardman-Jones)

‘Earth Vessel’ by Jenny Beavan. (47 × 34 × 12cm) Porcelain, with Shigaraki clay mixed with combustible material, volcanic and beach sands.Made in Japan in 1999.

‘Deer Pond’ fruit bowl by Carol McNicoll. Slip cast in Shigaraki porcelain with paper pulp.

The less formal, more abstract tiles and panels are decorated by first brushing a layer of pure porcelain slip, either white or coloured, over the surface. Subsequent layers of colour are built up by sponging, or brushing slip, onto selected areas. Resist techniques are used on some sections: wax, masking tape and a variety of mesh screens assist in adding pattern and texture to parts of the surface.

Work is dried slowly, over several days, between sheets of absorbent paper and weighted boards. They are once-fired to 1260°C in either an oxidized or a reduction atmosphere and finished by polishing with carborundum paper.

Whilst porcelain is generally used for its translucent, white characteristics, Jenny Beavan (UK) prefers to combine it with other clays and materials, resulting in richly textured pieces. Her work is reminiscent of the Cornish landscape and coastline where she lives. Describing her work, she says:

In all my making processes, I aim to achieve a balance between freedom of expression and consideration of order. For example, when building a random form, this form then presents suggestions about its chaotic structure. Transformation, by imposing action, necessitates spontaneous decision making, trust and willingness within a kind of relationship, in order to explore and create a new inner form whilst retaining elements of a former existence.

Jenny Beavan’s piece ‘Earth Vessel’ was made as a result of a four-month study period in Japan. A cylinder of porcelain was wrapped around a sheet of local Shigaraki clay mix and rolled together. Using a cutting wire, a section was removed, leaving a ‘U’ shaped form. This was left to find its own form, determined by the water content of the clay. The piece was fired to 1270°C in an electric kiln.

Ceramicist Carol McNicoll (UK) has also used Shigaraki clay whilst working as Guest Artist for the Japanese Foundation Millennium project in Japan. Her ‘Deer Pond’ fruit bowl was constructed from slip cast elements using the local porcelain casting slip, to which she added a small proportion of paper pulp. It was reduction-fired to 1270°C with a clear glaze using locally bought underglaze transfers.

2

Making Methods

Throwing

Porcelain

Porcelain can be considered a difficult clay to throw with, especially for beginners. However, once mastered its possibilities are endless. The secret lies in deciding on the most appropriate clay for the desired form, as well as understanding the structure of the form. What appears possible in stoneware or earthenware will be entirely different when made in porcelain. Quite apart from the plastic nature of this fine clay, shrinkage and distortion are both factors that need to be recognized and understood for successful results.

It is advisable first to do some testing to establish the nature of the clay. The ‘knot test’ is a method whereby the plasticity of a porcelain can be determined. Roll out a thin coil of clay and tie it in a knot. Observe what happens – some porcelains will form smooth knots, whilst others will crack. Those that crack are too short to be easily used for handbuilding.

As far as shrinkage is concerned, commercially produced bodies will have a shrinkage guide that varies depending on the type, firing and so on, but a rough estimate from plastic to fired porcelain is between 12–15% at a temperature of 1250°C.

Oval thrown and pierced form by Horst Göbbels. (18cm h.) TM 10 Limoges porcelain. Reduction-fired between 1280–1320°C.

Preparation

Cleanliness in the studio is paramount. Particles of rust from equipment or tools, as well as contamination from other clays, will undoubtedly affect the porcelain. Good preparation of the clay is essential. If you are working in large quantities, a de-airing pug mill is a valuable piece of equipment and thorough kneading is necessary to achieve the right consistency. Jack Doherty (UK) (seeChapter 6) recommends spiral kneading on a wooden surface and suggests avoiding rapid-drying on plaster bats as this will alter the plasticity of the porcelain, making it short and crumbly.

Tall ribbed jar by Jack Doherty. (50cm h.) Potclays Harry Fraser porcelain (1149). Once-fired and soda glazed to 1300°C. (Photo: Sue Packer)

‘Unfolding Vase’ by Takeshi Yasuda. (45cm h.) Limoges porcelain. Fired to 1300°C. 2002.