As a city dweller, I am intrigued by geometric shapes and the spatial dynamics in an urban landscape. While working with slip casting, I became dissatisfied with rounded vessels. Instead, I wanted to make a series of work that responded to my living environment as well as to the spatial relationship between the vessels and the human hand.
While the design for the geometric vessels was based on the conventional rounded form, the different facets of flat planes, angular turns, and undercuts enfold it into an abstraction. Seen from different angles, the geometric facets cast shadows onto each segment to create a soft-looking contour despite its angular form. While holding the vessel, users quickly feel the different attributes of space under the fingers and intuitively adjust the way they interact with or handle it. This allows the user to create a subtle spatial association through touch and to become more conscious of holding or drinking from the vessel.
I sketch the different possibilities for a vessel and think about the work’s functions. As I developed the designs for these geometric vessels, I referenced the facets from typical shapes, juxtaposing them together to form larger units. These units were interconnected into a composition around a circular format. A scaled-up, rough clay form was produced; it was made larger knowing that the final, fired, slip-cast form will shrink 15% (1).
The clay prototype was allowed to dry a bit before using a modified hacksaw blade, a Surform, and other tools to shape and create the angular cuts (2). The design was reworked several times over the course of a week to finalize the flow of the facets into one another.
Once the clay reached leather hard, the edges were defined with a knife blade, and the surface smoothed (3). After finalizing the shape of the prototype, I planned the best way to divide the mold into sections to avoid undercuts. The best approach was to divide the plaster parts along the angular lines of the facets, starting from the top and leading to the bottom to avoid ugly seam marks jutting through the surface of the planes in the finished work. Based on the undercuts and planar shifts, I determined that it could be a 3-part mold, but I chose to do a 5-part mold (4 sides and a separate base) to avoid complications with removing the piece from the mold.
To create the plaster mold in sections, slabs were used as partitions; they were extended along the edge, then reinforced from the back to prevent them from collapsing from the weight of the added plaster while pouring (4). A pour spout and reservoir for extra slip was created by extending the top of the vessel prototype using clay of a different color so it could be easily differentiated and cleared from the prototype during clean up (see 4). Three pieces of plywood were selected as cottle boards, and every wooden surface brushed with mold soap for easy plaster removal. The two cottle boards that attach to the sides of the clay partition were placed first and clay coils were added to seal the seam (5). The third, narrower board was placed opposite from the prototype and clay partitions, then clay coils were added to seal the seams. Next, clamps were placed around the mold (6).
After securing the cottle boards and ensuring all seams were sealed with clay coils, plaster was mixed and poured. This first section of the mold is the largest of the 5 pieces that will make up the mold. Since half the size of the mold is done (7), the rest of the partings and resulting plaster mold sections will be smaller. The unevenness on the plaster should be leveled (8), taking care not to create any undercuts that will prevent the releasing of the next mold piece or disturb the interface between the edges of the model and the plaster mold (8). Sandpaper is used to create a smooth surface. Keys were created by twisting a coin into the plaster (9).
Apply mold soap on the plaster surface liberally to ensure that the sections release after the plaster dries. Note: I have also found that olive oil works well as a separator. Wait for the soap to dry, then brush on five additional coats. Steps 4–9 are repeated to make the 4 other plaster cast partings (see 10–13).
The 5-Piece Mold
The 5-piece mold is heavy after it is filled with slip. In order to reduce the weight and effort needed to pour the slip out, some corners of the plaster mold were cut away using a hacksaw. The mold sections were separated using a wide bladed metal scraper, slowly hammering with a mallet into the gap between the partings. An air gun could also assist in releasing the sections of the mold. The mold was washed thoroughly, lightly polished with fine sandpaper and allowed to dry for a week before slip casting (14).
Separating the mold sections for the first time can cause plaster to accidentally chip off. Since the mold is still wet, some small areas could be repaired by adding more plaster. I have experimented with adding white glue into the plaster mixture when making these repairs. It is not foolproof, but the repair lasted through many rounds of slip casting with the mold.
Casting the Forms
After filling the mold (15), then draining it once the wall reached an appropriate thickness, the clay casting can be removed from the mold after it shrinks and pulls away from the plaster, or it can be released with an air gun after the clay has firmed up (16). If shrinkage cracks appear at the rim, they can be easily repaired with some added slip compressed into the cracks. Next, the flashing on the edges of the vessel caused by slip seeping into the seams between the mold sections during casting can be trimmed and then the piece dried slowly (17). After bisque firing, soak the vessel in water and smooth the surface with sandpaper. When dry, only the interior is glazed. The porcelain slip is a translucent clay to which colored stains can be added. When using colored slip, I pour the slip out after less than half the thickness of the wall has been built up. I use the normal slip for the other half. This creates two tones on the outside and inside.
Making plaster molds and slip casting can be messy, but once you have successful molds, it will more efficiently make forms that would otherwise be time consuming to handbuild.
the author Huey Ling Teo lives and works in Singapore. She studied at the Nanyang Academy of Fine Arts, Singapore, and later graduated with high distinction in both ceramics and drawing from the National Art School, Sydney, Australia. Follow her on Instagram @hueylingteo and http://teohueyling.blogspot.com.