Saggar

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Saggars in the Gladstone Pottery Museum
Saggars in use in the Manufacture nationale de Sèvres

A saggar is a ceramic, boxlike container used in the firing of pottery to enclose or protect ware in kilns. Traditionally saggars were made primarily from fireclay.[1][2] Saggars have been used to protect, or safeguard, ware from open flame, smoke, gases and kiln debris:[3] the name is a contraction of "safeguard".[4] Their use is widespread, including in China, Korea,[5] Japan and the United Kingdom. Saggars are still used in the production of ceramics to shield ware from the direct contact of flames and from damage by kiln debris.[6][7][8] Modern saggars are made of alumina ceramic, cordierite ceramic, mullite ceramic and silicon carbide.[9][10]

Staffordshire potbanks[edit]

By far the largest number of UK bone china manufacturers were based in and around Stoke-on-Trent in a region known as The Potteries. Their businesses known as potbanks fired their wares in distinctive bottle ovens. At the turn of the twentieth century over 4000 of these were in use while in 2014 only 47 survive, all of which are listed buildings. It was here that Josiah Wedgwood produced his china tableware and figurines. The highly decorated china required a white clay and consistent firing. The bottle oven was energy inefficient and the sulphurous fumes from the fires passed through the kiln. The ware was placed in saggars and biscuit fired, then glazed and again in saggars glost fired. It was then decorated, placed on ceramic bats and fired again in a sealed muffle kiln. Coal, china stone, clay and bone came into the towns by the Trent and Mersey Canal; which then took the products to Liverpool for export, or along the canal network for home use.

The saggars were used for the biscuit and the glost firing. They were expected to last for about 40 firings; each potbank made their own in a sagger making workshop. Saggars were made from fireclay, by a saggar maker and two assistants: the framemaker and the bottom knocker. The framemaker beat the clay into a sheet on a metal table using a large mallet, the mow or mawl. Using a frame he would cut it to size, sprinkle it with sawdust and wrap it round a wooden block to make the walls. The framemaker was usually an apprentice in his late teens. The bottom knocker, usually a boy in his early teens, did the same on a smaller scale, constructing the round or banjo-shaped bottom. Again the mow was used to beat the air out of the clay and flatten the sheet. The saggar maker was an experienced craftsman who paid his assistants out of his piece-work earnings: he took the bottom and the sides onto a wheel and using his thumbs joined the sides to the bottom.[11] The green saggars were dried and then placed on the top of bungs during the next firing of the kiln.

A Saggar Maker's Bottom Knocker[12] was a name considered sufficiently amusing for it to be featured on the television panel show What's My Line?.[11] Whilst saggar making was a skilled craft, bottom knocking was far less skilled, consisting of beating clay into a metal ring.[13]

Studio pottery use[edit]

From the twentieth century studio potters have used saggars to create decorative ceramic pieces.[14] In this use saggars are used to create a localised reducing atmosphere,[14] or concentrate the effects of salts, metal oxides and other materials on the surface of their ware.[15]

Some pots may be carefully prepared for saggar firing. One method creates a smooth surface covered with clay slip, terra sigillata, which responds particularly well to the saggar technique. This slip covering may be burnished to achieve a gloss. Prepared pots are nestled into saggars filled with beds of combustible materials, such as sawdust, less combustible organic materials, salts and metals. These materials ignite or fume during firing, leaving the pot buried in layers of fine ash. Ware produced in filled saggars may display dramatic markings, with colours ranging from distinctive black and white markings to flashes of golds, greens and red tones. Porcelain and stoneware are ideal for displaying the surface patterns obtained through saggar firing. In addition to the use of saggars, some studio potters bundle pots and burnable materials within a heavy wrapping of metal foil.

References[edit]

  1. ^ 'A Study of the Properties of Saggar Mixtures. Part XVIII: The Use of Fused Silica as Grog in Saggar Mixes.' White R.P, Rigby G.R. British Ceramic Research Association.RP13. 1948
  2. ^ 'Kiln Furniture Mixes Containing Highly Refractory Grog'. White R.P, Rigby G.R. British Ceramic Research Association. RP161. 1952
  3. ^ http://www.ironbridge.org.uk/learning/resources/resources/ccm.pdf.
  4. ^ 'The Concise Oxford Dictionary of English Etymology'. T.F. Hoad. Oxford University Press. 1996. Retrieved October 14, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-saggar.html
  5. ^ http://www.clickkorea.org/arts/curator/file/1-6_A%20Brief%20History%20of%20Korean%20Ceramics.pdf
  6. ^ 'Extending The Useful Life Of Saggars'. Karpova N.G., Voitovich V.A. Glass and Ceramics. Vol. 37, No 12. 1980
  7. ^ http://amic.biz/Data%20Brochure/AMI%20Kiln%20Furniture%20%28Cordierite-Mullite-Corundum%29.pdf.
  8. ^ http://www.ikf-solutions.com/pdf/KF%20for%20TC%20CFI%20April09.pdf.
  9. ^ 'Development Trend Of Dense Alumina Saggar For Electric Materials'. Hayashi K. Ceram. Jap. 38, No.8, 2003. pg.561-563
  10. ^ 'Silicon Carbide Sagar For Firing Non-oxide Ceramics.' Sakaguchi M., Taskeshita S., Hirota T., Aratani K., Kawakami T. Refractories in the Ceramics Industry. Aachen Proc., 32nd Int.Colloquium on Refractories Aachen, 12–13 October 1989, pg.75-78 Verlag Schmid GmbH
  11. ^ a b |Saggar making
  12. ^ http://www.adam-hart-davis.org/articles/Sagger-maker.htm
  13. ^ 'Automatic Saggar Handling Plants'. Lippert J., GmBH & Co. Pressath, 1991
  14. ^ a b http://members.iinet.net.au/~potters2/newsletters/tas-potters-news-june-06.PDF
  15. ^ Cort, Louise. Seto and Mino Ceramics. University of Hawaii Press, 1992, p. 68

External links[edit]