In the past, deciding when and how to apply terra sigillata was rather fixed; one must apply it before the bisque firing, and it should be burnished between layers. If a historically inspired use of terra sigillata is desired, then the application process should follow traditional approaches. Presently, the use of terra sigillata expands beyond the traditional method—when the burnished sheen and water-tight qualities are unnecessary, terra sigillata can be used for its waxy, skin-like coating, making an effective base surface that highlights sensitive mark making created during the object’s forming stages.
Because of the fine particle size and lack of a fusing layer, terra sigillata, when used alone, best adheres to the clay body when applied before the bisque firing. However, terra sigillata can be applied after the bisque firing or after multiple firings, but different processes and materials are needed to successfully adhere the terra sigillata to the form.
Other considerations for application include: surface qualities, structure and scale of the piece, and overall fragility of the unfired piece.
Leather Hard and Bone Dry
Applying terra sigillata by brushing or dipping at the leather-hard state naturally encourages, or creates, a waxy burnished-like sheen without the burnishing process. However, because there is elevated moisture content in the clay, the terra sigillata sits on the surface rather than being absorbed by the clay surface. This results in a less opaque covering of terra sigillata. This could be an interesting application when a semi-translucent layering effect is desired.
At the bone-dry state, when clay is the driest before the bisque firing, the brushed or dipped terra sigillata is more deeply absorbed into the clay’s outer surface, allowing more layers of terra sigillata to be built up, thereby creating a more uniform and opaque surface. This stage of clay is also when the clay is at its most fragile state, and care must be given when applying the terra sigillata.
How Many Layers?
Traditional terra sigillata application process advises no more than three brushed layers of terra sigillata be applied, otherwise flaking and peeling become more likely after the bisque firing. This suggestion assumes the terra sigillata has a specific gravity of 1.15.
If the terra sigillata is thinner, with a specific gravity of 1.10, more layers will need to be applied to reach an opaque surface or to create visual depth with multiple colored layers. With a more watery composition, single brushed on layers of terra sigillata will result in translucency, which is both potentially disappointing or advantageous depending on your goals for the surface of your piece.
Conversely, if the specific gravity is closer to 1.20, then fewer layers should be applied to avoid peeling terra sigillata.
Application for Translucent Effects
The translucent quality of terra sigillata can be used to your advantage in a variety of ways. Often, terra sigillatas appear very flat because of their opaque, flat nature. Thinner application layers allow a depth of color to be created by allowing colors from below to filter through layers above.
Timing and Pace of Application
Because terra sigillata is often applied at the most fragile state of clay, bone dry, it is important to consider the overall fragility of your piece. To avoid cracking in the application process, aim to apply the terra sigillata as quickly and as evenly as possible, regardless of the application method (brush, dip, or spray). Thinner clay forms are at greater risk of cracking during the terra sigillata application process. If one area of the piece becomes over-saturated with terra sigillata, it will likely cause cracking in the piece due to the difference in moisture content throughout the piece. In your beginning stages of working with terra sigillata, consider practicing the application process on pieces of lesser preciousness.
Soft- Versus Stiff-Bristle Brushes
When brushing on terra sigillata, remember that it reflects a history of its application because it has no glass formers, or flux, to melt away marks. A stiff-bristle brush will leave brush marks, and these could be considered a distraction, or they could be used to enhance the textural qualities of the terra sigillata surface.
A soft-bristle brush will be less likely to leave brush marks, but some soft-bristle brushes leave hairs behind in the application process, and these, too, will remain as surface marks in the fired terra sigillata. Burnishing the terra sigillata after application can remove any unwanted marks, so finding the right brushes for your application preferences can keep your process moving along.
Light Over Dark Process
Begin by brushing on a single layer of dark terra sigillata, like Rhonda’s Blue/Black Terra Sigillata, with a soft-bristle brush. Allow this layer to dry to the touch, lightly rub to burnish the surface; only a couple of gentle swipes of your hand are necessary. Next, apply a layer of light-colored terra sigillata (see recipe for a white terra sigillata). The darker layer will be semi-visible beneath the lighter terra sigillata layer (1).
Using marking tools, such as a manicurist’s dotting tool or a needle tool, begin making designs. The dotting tool can be used to make dots as intended, or it can be used to lightly carve the terra sigillata (2). A miniature loop carving tool creates variable lines and shapes that carve through both layers of terra sigillata, revealing the clay layer below (3). The needle tool, used like a pencil, scratches the surface, allowing delicate lines and hatch-like marks to be made through the terra sigillata layers (4).
Use a duster brush to remove the tiny clay burrs from the carving process (5). The resulting exterior surface has layered values and scales of marks (6).
I use many of the same tools on the interior (7, 8). A standard pottery tool kit’s wooden modeling tool is used to age a stripe of white terra sigillata (9, 10).
After the initial bisque firing, the Rhonda’s Blue/Black Terra Sigillata darkens and becomes more apparent through the carvings and marks (11, 12).
Learn more about terra sigillata in Rhonda Willers’ book, Terra Sigillata: Contemporary Techniques, published by The American Ceramic Society and available in the Ceramic Arts Network shop at ceramicartsnetwork.org/shop.
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In the past, deciding when and how to apply terra sigillata was rather fixed; one must apply it before the bisque firing, and it should be burnished between layers. If a historically inspired use of terra sigillata is desired, then the application process should follow traditional approaches. Presently, the use of terra sigillata expands beyond the traditional method—when the burnished sheen and water-tight qualities are unnecessary, terra sigillata can be used for its waxy, skin-like coating, making an effective base surface that highlights sensitive mark making created during the object’s forming stages.
Because of the fine particle size and lack of a fusing layer, terra sigillata, when used alone, best adheres to the clay body when applied before the bisque firing. However, terra sigillata can be applied after the bisque firing or after multiple firings, but different processes and materials are needed to successfully adhere the terra sigillata to the form.
Other considerations for application include: surface qualities, structure and scale of the piece, and overall fragility of the unfired piece.
Leather Hard and Bone Dry
Applying terra sigillata by brushing or dipping at the leather-hard state naturally encourages, or creates, a waxy burnished-like sheen without the burnishing process. However, because there is elevated moisture content in the clay, the terra sigillata sits on the surface rather than being absorbed by the clay surface. This results in a less opaque covering of terra sigillata. This could be an interesting application when a semi-translucent layering effect is desired.
At the bone-dry state, when clay is the driest before the bisque firing, the brushed or dipped terra sigillata is more deeply absorbed into the clay’s outer surface, allowing more layers of terra sigillata to be built up, thereby creating a more uniform and opaque surface. This stage of clay is also when the clay is at its most fragile state, and care must be given when applying the terra sigillata.
How Many Layers?
Traditional terra sigillata application process advises no more than three brushed layers of terra sigillata be applied, otherwise flaking and peeling become more likely after the bisque firing. This suggestion assumes the terra sigillata has a specific gravity of 1.15.
If the terra sigillata is thinner, with a specific gravity of 1.10, more layers will need to be applied to reach an opaque surface or to create visual depth with multiple colored layers. With a more watery composition, single brushed on layers of terra sigillata will result in translucency, which is both potentially disappointing or advantageous depending on your goals for the surface of your piece.
Conversely, if the specific gravity is closer to 1.20, then fewer layers should be applied to avoid peeling terra sigillata.
Application for Translucent Effects
The translucent quality of terra sigillata can be used to your advantage in a variety of ways. Often, terra sigillatas appear very flat because of their opaque, flat nature. Thinner application layers allow a depth of color to be created by allowing colors from below to filter through layers above.
Timing and Pace of Application
Because terra sigillata is often applied at the most fragile state of clay, bone dry, it is important to consider the overall fragility of your piece. To avoid cracking in the application process, aim to apply the terra sigillata as quickly and as evenly as possible, regardless of the application method (brush, dip, or spray). Thinner clay forms are at greater risk of cracking during the terra sigillata application process. If one area of the piece becomes over-saturated with terra sigillata, it will likely cause cracking in the piece due to the difference in moisture content throughout the piece. In your beginning stages of working with terra sigillata, consider practicing the application process on pieces of lesser preciousness.
Soft- Versus Stiff-Bristle Brushes
When brushing on terra sigillata, remember that it reflects a history of its application because it has no glass formers, or flux, to melt away marks. A stiff-bristle brush will leave brush marks, and these could be considered a distraction, or they could be used to enhance the textural qualities of the terra sigillata surface.
A soft-bristle brush will be less likely to leave brush marks, but some soft-bristle brushes leave hairs behind in the application process, and these, too, will remain as surface marks in the fired terra sigillata. Burnishing the terra sigillata after application can remove any unwanted marks, so finding the right brushes for your application preferences can keep your process moving along.
Light Over Dark Process
Begin by brushing on a single layer of dark terra sigillata, like Rhonda’s Blue/Black Terra Sigillata, with a soft-bristle brush. Allow this layer to dry to the touch, lightly rub to burnish the surface; only a couple of gentle swipes of your hand are necessary. Next, apply a layer of light-colored terra sigillata (see recipe for a white terra sigillata). The darker layer will be semi-visible beneath the lighter terra sigillata layer (1).
Using marking tools, such as a manicurist’s dotting tool or a needle tool, begin making designs. The dotting tool can be used to make dots as intended, or it can be used to lightly carve the terra sigillata (2). A miniature loop carving tool creates variable lines and shapes that carve through both layers of terra sigillata, revealing the clay layer below (3). The needle tool, used like a pencil, scratches the surface, allowing delicate lines and hatch-like marks to be made through the terra sigillata layers (4).
Use a duster brush to remove the tiny clay burrs from the carving process (5). The resulting exterior surface has layered values and scales of marks (6).
I use many of the same tools on the interior (7, 8). A standard pottery tool kit’s wooden modeling tool is used to age a stripe of white terra sigillata (9, 10).
After the initial bisque firing, the Rhonda’s Blue/Black Terra Sigillata darkens and becomes more apparent through the carvings and marks (11, 12).
Learn more about terra sigillata in Rhonda Willers’ book, Terra Sigillata: Contemporary Techniques, published by The American Ceramic Society and available in the Ceramic Arts Network shop at ceramicartsnetwork.org/shop.
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