Terra sigillata

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Roman red gloss terra sigillata bowl with relief decoration
Terra sigillata beaker with barbotine decoration.

Terra sigillata is a finish and decorating medium used on ancient Middle Eastern and Mediterranean ceramics, especially Ancient Roman pottery, which has experienced a resurgence in popularity in contemporary studio pottery. "Terra sig" can be made from any kind of naturally occurring clay, mixed as a very thin liquid slip and settled to separate out only the finest particles to be used as terra sigillata. When applied to greenware (unfired) clay surfaces, "terra sig" can be polished with a soft cloth or brush to achieve a shine ranging from a smooth silky luster to a high gloss. The polished surface can only be retained if fired within the low-fire range and will lose its shine if fired higher, but can still display an appealing silky quality. Traditionally, terra sigillata was only used on low-fired earthenware.

Contents

History

Red Glossed Ware

Terra sigillata (or "stamped earth") is a name for two distinct items in antiquity. First, it is one term by which decorated red-glossed Ancient Roman pottery was, and is, known. In English usage it is sometimes restricted to Samian ware, excluding Arretine ware and other types such as African Red Slip - in Italian and other languages it is used more widely. These were the dominant type of fine Roman pottery from about 50 BCE to the later Empire.[1] Definitions are not entirely consistent; one survey of Classical art says:
Terra sigillata ... is a Latin term used by modern scholars to designate a class of decorated red-gloss pottery .... It should be noted that not all red-gloss ware was decorated, and hence the more inclusive term 'Samian ware' is sometimes used to characterize all varieties of it.[2]

- whereas Anthony King's definition does not insist on "decorated", and says terra sigillata is "alternatively known as samian ware"[3] Scholars increasingly use "red glossed ware" to avoid these issues of definition.[4].

Medicinal Soil

Secondly, it was a term for a medicinal soil from the island of Lemnos. The latter was called "sealed" because cakes of it were pressed together and stamped with the head of Artemis. Later, it bore the seal of the Ottoman sultan. This soil's particular mineralic content was such that, in the Renaissance, it was seen as a proof against poisoning, as well as a general cure for any bodily impurities, and it was highly prized as a medicine and medicinal component.

Modern Usage

In contemporary Ceramic Art, Terra sigillata describes a watery refined slip used to facilitate the burnishing of raw clay surfaces and used to promote carbon smoke effects, in both primitive low temperature firing techniques and unglazed alternative western-style Raku firing techniques. Terra sigillata is also used as a brushable decorative colorant medium in higher temperature glazed ceramic techniques.

Making Terra Sigillata

Modern terra sigillata is made by adding a deflocculant such as Sodium Silicate to a watery clay/water slip mixture and then allowing the clay particles to separate into layers by weight. For undisturbed deflocculated slip settling in a transparent container, these layers are usually visible within 24 hours. Siphoning off the topmost layers of slip, which contain the smallest and lightest clay particles, produces terra sigillata. The remaining heavier settled layers of deflocculated clay slip are discarded.

Application

Terra sigillata is usually brushed or sprayed in thin layers onto dry or almost dry raw clay ware. The ware is then quickly burnished with a soft cloth before the water in the terra sigillata is absorbed by the raw clay. The burnished ware is allowed to dry again to remove the added moisture and bisque fired, often fired to a lower than normal bisque temperature of approximately 900C. Higher firing temperatures tend to remove the burnished effect in the clay surface.

References

See Also

External links

Notes

  1. King, 253 (definition) and 183-186.
  2. Boardman, pp. 276-77
  3. King, 253. See also the British Museum
  4. As both King and Boardman do in their main texts.

References

External links