Slip casting

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Slip casting, or slipcasting, is a ceramic forming technique for pottery and other ceramics, especially for shapes not easily made on a wheel.[1] In this method, a liquid clay body slip (usually mixed in a blunger) is poured into plaster moulds and allowed to form a layer, the cast, on the inside walls of the mould. The process usually takes at least 24 hours per piece.[2][3] It gives very precise and consistent shapes, and is now the most common technique used for commercial mass-produced pottery,[4][5] although it began as a technique for fine pottery such as European porcelain in the 1750s,[6] and Chinese Jingdezhen porcelain considerably earlier.

Small-scale slip casting workshop of the manufacture nationale de Sèvres. Preparation of the firing supports
External video
video icon How it's made: Ceramic Slip Casting
video icon "Slip Casting at the Emma Bridgewater factory in Stoke-On-Trent, England
Some of the shapes made in the small-scale slip casting workshop of the manufacture nationale de Sèvres

The type of clay body suited for slip casting differs from that for throwing.[2] It is essential to make a good quality casting slip to get an intended result. The behavior of the slip will depend on multiple factors, including the types and proportions of water, clay, other chemicals, and deflocculant used; temperature, humidity and other local conditions; and the amount of energy involved in mixing the ingredients together to form a suspension. The process of changing a slurry from something thick and gooey to something thin and pourable that can be used in slip casting is called deflocculation. The process by which particles come out of the suspension is called flocculation.[7][8][9]

The technique is suited to the production of complex shapes, especially if with relief decoration and thin walls. Much modern fine factory porcelain is made by the technique, very often the entire production. It is also commonly used for sanitaryware, such as toilets and basins, and smaller pieces like figurines and teapots.[10][11] The technique can also be used for small-scale production runs or to produce limited edition, one off objects, especially reproductions of antique dolls and modern porcelain doll-making.[12]

Technical considerationsEdit

Accurately measuring the viscosity and specific gravity of a slip is important for determining whether it is properly mixed and ready to use. The specific gravity should be measured and adjusted before making adjustments to the viscosity.[13] The amount of time needed to form a casting will vary with the type of slip used in the casting.[14]

 
Part of a mould for making a teapot
 
Removing the last parts of a mould from a slip casting

In a solid cast mould, ceramic objects such as handles and plates are surrounded by plaster on all sides with a reservoir for slip, and are removed when the solid piece is held within. For a hollow cast mould, for objects such as vases and cups, once the plaster has absorbed most of the liquid from the outside layer of clay the remaining slip is poured off for later use. After a period for further absorption of water, the cast piece is removed from the mould once it is leather-hard, that is, firm enough to handle without losing its shape. It is then "fettled" (trimmed neatly) and allowed to dry out further, usually overnight or for several hours. This produces a greenware piece which is then ready to be decorated, glazed and fired in a kiln.[10]

As a processing technique for ceramic laminates, a ceramic powder is often placed in suspension to form a slip with a high solids content (>60 wt%) as well as a very low viscosity value (<40 mPa). The suspension is poured into a porous mold. As the mold dries, a solid particulate layer is formed on the mold through deposition of the solids in the slip. A series of ceramic layers can be formed by changing the composition of the slips used in repeated castings. If the chemistry of the materials being used is well understood, the thickness of the layers can be controlled by varying the length of time involved in the casting.[15]

An additive with deflocculant properties, such as sodium silicate, can be added to the slip to disperse the raw material particles. This allows a higher solid content to be used, or allows a fluid slip to be produced with a minimum of water so that drying shrinkage is minimised, which is important during slip casting.[16]

SlipwareEdit

Slip cast ware, objects that are formed using slip casting, should not be confused with slipware, pottery that is formed by any technique and then decorated using slip.[17] The French for slip is barbotine (coulée en barbotine means slip casting). As far back as the Roman empire, potters created what is termed "Barbotine ware" by using clay slip to decorate the surface of pots.[18] "Barbotine pottery" is sometimes used for 19th century French and American pottery with added slip cast decoration,[19] as well as (confusingly) 17th English slipware that is decorated with thick blobs of slip.[20]

ReferencesEdit

  1. ^ Morgenthal, Deborah; Tourtillott, Suzanne J. E., eds. (2008). The Penland Book of Ceramics: Master Classes in Ceramic Techniques. New York: Lark Books; Sterling Publishing Company, Inc. p. 72. ISBN 978-1-60059-275-1. Retrieved 16 October 2021.
  2. ^ a b Martin, Andrew (2006). The Essential Guide to Mold Making & Slip Casting. New York: Lark Books; Sterling Publishing Company. pp. 117–143. ISBN 978-1-60059-077-1. Retrieved 16 October 2021.
  3. ^ "Glossary of Ceramic Terms | Walker Ceramics". Walker Ceramics Australia. Retrieved 16 October 2021.
  4. ^ Rijke, Jenny (March 4, 2020). "Slip Casting Molds: What are they, why use them and how to achieve different aesthetics". Jenny RIjke. Retrieved 16 October 2021.
  5. ^ Toma, McKenzie (August 29, 2018). "What Even Is Slipcasting?". East Fork. Retrieved 16 October 2021.
  6. ^ Paxton, John L.; Fairfield, Sheila (18 June 1980). Calendar of Creative Man. London and Basingstoke: Macmillan International Higher Education. p. 273. ISBN 978-1-349-02577-0. Retrieved 16 October 2021.
  7. ^ "Deflocculation". DigitalFire.com Reference Library. Retrieved 16 October 2021.
  8. ^ Gadow, Rainer; Kern, Frank (1 January 2014). "2.06 - Advanced Manufacturing of Hard Ceramics". Comprehensive Hard Materials. Amsterdam: Elsevier. pp. 207–230. ISBN 978-0-08-096528-4.
  9. ^ Wandless, Paul Andrew. "How to Make Casting Slip from Your Clay Body - A Simple Technique". Ceramic Arts Network Daily. Retrieved 16 October 2021.
  10. ^ a b Osborne, Harold (1975). The Oxford companion to the decorative arts. Oxford: Clarendon Press. p. 746. ISBN 0198661134.
  11. ^ Bhargava, A. K. (2012). Engineering Materials : polymers, ceramics and composites (Second ed.). New Delhi: PHI Learning Pvt. Ltd.,. p. 196. ISBN 9788120346215. Retrieved 16 October 2021.CS1 maint: extra punctuation (link)
  12. ^ "Casting Your Miniature Doll Molds". Cynthis Howe Miniatures. Retrieved 16 October 2021.
  13. ^ "Reference Guide To Making and Adjusting Casting Slip". The Ceramic Shop. Retrieved 16 October 2021.
  14. ^ "Slip-casting for beginners". ClayCraft. 16 November 2017. Retrieved 16 October 2021.
  15. ^ Chan, Helen M. (August 1997). "LAYERED CERAMICS: Processing and Mechanical Behavior". Annual Review of Materials Science. 27 (1): 249–282. doi:10.1146/annurev.matsci.27.1.249. ISSN 0084-6600. Retrieved 15 October 2021.
  16. ^ Singer, Felix; Singer, Sonja S. (1971). Industrial Ceramics. London: Chapman & Hall. ISBN 9788120401624.
  17. ^ Hamer, Frank; Hamer, Janet (23 June 2004). The Potter's Dictionary of Materials and Techniques. Philadelphia: University of Pennsylvania Press. pp. 333–334. ISBN 978-0-8122-3810-5. Retrieved 16 October 2021.
  18. ^ Cooper, Emmanuel (2000). Ten Thousand Years of Pottery. Philadelphia: University of Pennsylvania Press. p. 52. ISBN 978-0-8122-3554-8. Retrieved 16 October 2021.
  19. ^ Frelinghuysen, Alice Cooney; Eidelberg, Martin; Spinozzi, Adrienne (25 September 2018). American Art Pottery: The Robert A. Ellison Jr. Collection. New York: Metropolitan Museum of Art. p. 43. ISBN 978-1-58839-596-2.
  20. ^ "Pottery - 17th-century slipware". Encyclopedia Britannica.