How Did Romans Make Terra Sigillata?

Terra sigillata, meaning “sealed earth” in Latin, refers to a bright red glossy pottery that was mass-produced and widely distributed across the Roman Empire from the late 1st century BC to the 3rd century AD.

It is characterized by its thin walls, bright glossy surface slip coating, and decorative motifs stamped into the unfired clay. Terra sigillata was an important part of material culture in the Roman world and was both functional as tableware and decorative.

The production process involved skilled potters working on potter’s wheels to shape the vessels, which were then dried, fired, and coated with a glossy slip made from a refined clay source. The slip helped waterproof the vessel and gave it its signature shiny red finish. Molds and stamps were used to imprint decorative designs during the leather-hard unfired stage.

Terra sigillata was made in many production centers across the Roman world, but the major sources were in modern-day Italy, Gaul, and Germany. The pottery was widely traded and distributed, allowing local styles and decorative motifs to spread across the empire.

Clay Sources

Terra sigillata was made from specific types of clay that were sourced from certain locations across the Roman Empire. According to Terra Sigillata 101: How to Make, Apply & Troubleshoot …, the clay used often came from deposits around modern day Cologne in Germany as well as deposits in France and other areas of Western Europe.

The properties that made these clays ideal for terra sigillata production include their high kaolin content, which results in smooth surfaces, as well as finer particles and high plasticity that allow for thin vessel walls. Clays like these were able to hold fine detail well. Specific clay types used include ball clays, kaolin, and local clays near production areas. According to How to Make Terra Sigillata | Easy Peasy Terra Sig, clays like Redart, Albany, and Barnard clay were common choices during Roman times.

Clay Preparation

The clay used for terra sigillata needed to be extremely refined and pure to create the smooth surface and high gloss finish. To achieve this, potters engaged in an extensive process of levigation and mixing.

Levigation involves suspending the clay particles in water and allowing them to settle over time. The larger particles will settle first, while the extremely fine clay particles will remain suspended in the water. The water can then be poured off, leaving behind only the finest clay particles. This process is repeated multiple times to further purify and refine the clay (Georgies).

The levigated clay would be consolidated and mixed with water to achieve an even distribution of particle sizes and smooth consistency ideal for applying the terra sigillata slip. Additional levigation or sieving could be done at this stage to remove any remaining coarse particles. The end result is an extremely fine clay slip ready for application on the pottery vessels.

Potter’s Wheel

The potter’s wheel was an essential tool used by Roman potters to shape terra sigillata vessels. The wheel enabled potters to efficiently produce thin-walled vessels with symmetrical shapes and refined surfaces ideal for applying decorative slips (Terra Sigillata 101: How to Make, Apply & Troubleshoot …, 2024). Bowls, plates, cups and other terra sigillata vessels were centered on the wheel upside down and shaped by the potter’s hands as the wheel spun at a constant speed. The rotational forces allowed potters to stretch, thin and refine vessel walls to precise thicknesses and create uniform curves and profiles. High quality terra sigillata required mastery of the potter’s wheel to shape flawless forms that could showcase elaborate decorative slips.

Drying and Trimming

After the terra sigillata vessels were shaped on the potter’s wheel, they needed to dry completely before moving to the next steps. The clay items were set aside and allowed to air dry slowly to prevent cracking and warping. This drying process could take several days or even weeks depending on the size and thickness of the pieces.

Once bone dry, the vessels were carefully trimmed to remove any excess clay and refine the shape. Trimming involved using a metal rib or knife to gently scrape and smooth the surface while the pot spun on the wheel. Skilled Roman potters aimed for thin, elegant walls and symmetrical profiles. Any minor cracks, chips, or uneven areas were repaired at this stage before decorating. According to Ceramic Arts Network, terra sigillata was always applied to bone dry or nearly bone dry wares.

Decoration

One of the most distinctive features of terra sigillata was the decorative motifs added to the surface of the vessels. Potters used molds made of clay, stone or metal to imprint designs and patterns into the clay before firing. Some common motifs included mythological creatures, floral patterns, geometric shapes, and scenes of gods, goddesses or nature.

The molds allowed for mass production of decorated sigillata wares. Potters would press the interior or exterior surface of the vessel into the mold, leaving an impression in the clay. The molded motifs created texture and visual interest. Stylized plant forms, like laurel leaves, acanthus scrolls and tendrils, were prevalent decorative elements.

Decorative friezes with repeating borders were also popular. The friezes often contained figures from Roman mythology or daily life. Intricate molded designs increased the value and appeal of the sigillata vessels. The red slip coating covered and highlighted the molded decorations.

According to this source, the most prolific sigillata production centers became well-known for their particular decorative styles and motif molds. For example, potters in Gaul favored vertical friezes while those in Italy specialized in mythological scenes. The decorated surfaces of terra sigillata gave it an aesthetic advantage over plain utilitarian pottery.

Firing Process

The firing process for terra sigillata required multiple firings in updraft kilns to achieve the characteristic red gloss finish. According to Pottery Making Illustrated, terra sigillata pieces were fired in updraft kilns that reached temperatures between 1,832-2,372°F (1,000-1,300°C). Updraft kilns allowed heat to rise gradually and flames to move over the pottery, helping to develop the glossy terra sigillata surface.

The firing process involved multiple firings. The bisque firing was done first to harden and prepare the clay body. Next, the first terra sigillata firing occurred at a lower temperature around 1,832°F (1,000°C) to mature the terra sigillata coating. One or more additional firings followed at higher temperatures between 2,192-2,372°F (1,200-1,300°C) to fully develop the red polished surface. Firing terra sigillata required precision and experience to achieve the brilliant red finish consistently.

Slip Coating

To achieve the characteristic red glossy finish, terra sigillata wares were coated with a very thin layer of refined slip called terra sigillata slip. This slip consisted of an extremely fine clay suspension made from refined kaolinitic clay sources (Terra Sigillata 101: How to Make Apply and Troubleshoot Terra Sig. Ceramic Arts Network, 2024. https://ceramicartsnetwork.org/daily/article/Terra-Sigillata-101-How-to-Make-Apply-and-Troubleshoot-Terra-Sig). The clay was refined through levigation, a process involving mixing the clay in water and allowing the heavier particles to settle out over time, leaving behind a very smooth and fine suspension. This was further enhanced by adding a deflocculant like sodium silicate to prevent clumping and flocculation (How to Make Terra Sigillata | Easy Peasy Terra Sig. The Pottery Wheel, 2020. https://thepotterywheel.com/how-to-make-terra-sigillata/).

The terra sigillata slip was applied in multiple thin coats to the bone-dry ceramics, resulting in a smooth, glossy surface. Each coat was allowed to dry before applying the next. The wares could be burnished or polished while the slip was wet to further enhance the shine. Firing at about 1800°F resulted in the characteristic deep red color due to the oxidizing atmosphere.

Distribution

Terra sigillata was widely traded and distributed across the Roman Empire due to the extensive trade routes that connected the various Roman provinces. The major production centers were located in Italy, Gaul, and the Rhineland, and vessels made their way from these areas throughout the Empire.

Gaul was one of the main exporters of terra sigillata. Samian ware from La Graufesenque in southern Gaul has been found in large quantities throughout Roman Britain, the Rhineland, the Danube frontier, Italy, North Africa, and the eastern Mediterranean [1]. The scale of production at La Graufesenque and other Gaulish sigillata centers indicates that terra sigillata was produced specifically for export markets.

Italy also exported terra sigillata across the Empire. Arretine ware made in Arezzo was a high-quality Italian sigillata that reached its peak production in the Augustan period. It has been found as far away as India and the Black Sea [2]. Arretine ware declined around 40-30 BC when samian ware from Gaul became dominant.

The extensive Roman road networks and maritime trade routes enabled the large-scale distribution of terra sigillata across the provinces. Its widespread presence at archaeological sites indicates it was considered a high-status tableware and enjoyed by Romans throughout the Empire.

Conclusion

Terra sigillata was an important type of Roman pottery that was widely distributed across the Roman Empire from the 1st century BCE to the 3rd century CE. Its bright red glossy surface and refined decoration made it a desirable tableware and serving vessel. The production process was complex, requiring high quality clay sources, careful refinement and processing of the clay, skilled potters to throw and trim the vessels on a wheel, intricate decorative techniques like barbotine trailing, and specialized firing conditions to create the glossy slip coating and vivid red color.

The wide distribution and longevity of terra sigillata speaks to its cultural and economic significance in the Roman world. As a high status tableware, it was an indicator of Romanization and connected even the farthest reaches of the Empire to Roman customs and lifestyles. The centralized production in large pottery workshops, along with widespread trade networks, allowed terra sigillata to reach consumers across Europe, North Africa, and the Middle East. Even after the Roman Empire declined, terra sigillata remained influential, with potters continuing to imitate its distinctive decorative styles and bright red finish.