Book: Ceramics - Art or Science? Author: Dr. Stan Jones

7. Pottery Technology 1

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7.15 Fritware (Stonepaste)

Early on, Egyptian potters added clay to the original faience constituents to make it more workable, and as a result it became stronger. As time went on ground glass was added so that the main constituents became typically 10% white clay, 10% ground glass and 80% quartz. From Islamic times considerable experimentation took place in Persia based on the Egyptian technology. This “fritware” was developed until it rivalled porcelain in its fineness and ability to be made into very thin-walled vessels in the Seljuk Period (1,037-1194 AD). In the 18th century European soft-paste porcelain was probably derived from this technology, as it was made from white clay, ground glass frit and sometimes ground calcined (roasted) bones or steatite. Calcining entails heating materials such as ores at a sufficiently high temperature for them to thermally decompose, but below their melting temperature.

7.16 Mosaics

Mosaics are pictures made up of a multitude of small coloured components. The Greeks regularised these components as cubes or dice called tesserae. Most tesserae are coloured stone, but ceramics were sometimes included, as well as glass from the Hellenistic period (323-30 BC) onwards. The Greeks also used terracotta threads as contours in some of their mosaics. For example, in the 4th century BC in Pella, Greece, long strips of terracotta were used to precisely delineate limbs and features. The Romans probably employed Greek mosaic artists to gain the technology that they used widely. Unless the base for the mosaic was adequate, the tesserae would dislodge and the mosaic would break up. For pavement mosaics the Romans would start with a thick stone foundation followed by a waterproof layer of tar or resin and two or three layers of mortar. Smaller areas would then have a fine mortar (possibly including marble or brick dust) applied into which the tesserae would be set. If applied to walls, nails would be used to help support the mortar. Sketches were made on the final sub-surface of the patterns and information on the colours to be used, which are now hidden under the Mosaics. Some of the more intricate mosaics found in Pompeii, having very small tesserae, were first set into terracotta trays that were then embedded into the mortar.

Roman Period Mosaics Pompei - source Wikipedia

Roman Period Mosaics Pompei
- source Wikipedia

This method was also used in ceilings, for example in the cupola mosaic in the church in Thessalonica, which was installed in 400 AD. The Byzantines frequently used terracotta tesserae for red objects and garments together with coloured stones. The Greeks continued to be the mosaic experts and their craftsmen were employed in 965 AD to produce the mosaics in the mosque at Cordoba, Spain.

7.17 Pottery Marks

Chinese Ming Jiajing Imperial Bowl with Six Character Jiajing Mark - courtesy R&G McPherson Antiques

Chinese Ming Jiajing Imperial Bowl with
Six Character Jiajing Mark - courtesy
R&G McPherson Antiques

“Signatures”, or more accurately names, are found on wares as early as ancient Greek vases. Also some Roman sigillata pottery was “signed” with stamps. Interestingly, fingerprints of a potter have been found under the glaze of Roman pottery in London and can be matched to other pieces he made. Chinese Imperial potters selected only perfect pieces to work on and rejected the rest, and “reign” marks were only supposed to be applied to Imperial pottery. However their use soon became widespread. Chinese porcelain marks usually record the dynasty and name of the Emperor.

Maker’s marks became common from 18th century in Europe, namely on Meissen, Sevres, Worcester and many more wares.

7.18 Copies and Fakes

Not all copies were made for financial gain, although many were. The practice of Chinese potters to manufacture pottery items identical to those made by their ancestors with identical marks as a mark of respect makes identification of real dates difficult.

Chinese Xuande Mark (1426-35) on a Jiajing Ming Bowl (1522-66) - courtesy R&G McPherson Antiques

Chinese Xuande Mark (1426-35) on a Jiajing
Ming Bowl (1522-66) - courtesy R&G
McPherson Antiques

It also explains why on many occasions such Chinese pots marked with low estimates in auctions as “19th century copies” are bid to high prices as two, perhaps better informed, bidders believe them to be the genuine article. Accordingly all pottery marks have to be treated with some scepticism, and great care taken in purchasing pottery to avoid costly mistakes.

There are a variety of techniques that help to determine the origins and dates of manufacture of pottery items. Modern technology permits analysis of the clay body in terms of composition, texture, hardness, colour and mineral content. Along with shape, style, decoration and firing, these methods can all point to production centres, manufacturing dates and suggest market areas. Sometimes detective work is needed, as with some medieval pottery found to contain Cotswold Oolite stone temper, but it was in fact made in Worcester, which is in an area where this stone does not exist naturally. The misleading stone came from the waste left during the building the cathedral! Thermoluminescence techniques can be used for dating the pot itself by taking a small sample and determining the number of years since firing, as firing “zeros” the internal radioactivity that then rebuilds. The previously mentioned carbon 14 dating can be used for associated organic material, for example bone or wood that starts to decay on death. These two methods are relatively expensive and are used only on high value items. Recently, scientists in Australia have come up with a non-destructive, detailed chemical fingerprinting of the composition of certain Japanese pieces, using a laser and specialised spectrometry, and believe this can identify the geographic area of manufacture and even the kiln used. This is clearly an area that will develop in the future.

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