Advanced Throwing Shapes
When a potter tries to build a tall lidded jar, the clay often collapses under its own weight before the form is finished. This common struggle mirrors the structural challenges faced by architects designing skyscrapers, where base support determines the height and stability of the entire building. To create complex vessels, you must master the art of sectional throwing, which involves creating distinct parts that later unite into one solid piece. This technique allows for grander scales and intricate shapes that are impossible to achieve when throwing from a single, heavy lump of clay on the wheel.
Mastering Sectional Construction
Because large amounts of wet clay tend to slump, you should throw your vessel in separate, manageable sections. Each section must be carefully measured to ensure the pieces align perfectly during the final assembly process. As you work, keep the rims of each section slightly thicker than the walls to provide structural integrity for the next layer. Think of this process like building a stone wall, where each layer must be level and sturdy to support the weight of the layers above it. If one section is too thin or uneven, the entire vessel will likely warp or crack during the drying phase.
Key term: Sectional throwing — a ceramic technique involving the creation of multiple separate clay parts that are joined together to form a single, complex vessel.
Once you have thrown your individual sections, you must allow them to reach the leather-hard state before you attempt any assembly. This specific firmness is critical because it provides enough rigidity to hold the weight of the next section without sagging. If the clay is too soft, the bottom section will deform under the pressure of the added weight. If the clay is too dry, the sections will fail to bond properly, leading to structural failure during the firing process. Timing your assembly is the most important skill for ensuring that your complex vessel remains stable and symmetrical throughout the entire construction.
Joining and Finishing Techniques
After achieving the correct state of dryness, you must prepare the connection points to ensure a seamless bond between the individual parts. You should score the edges of each section with a needle tool to create a rough surface that holds the liquid clay, known as slip, more effectively. Apply a generous amount of slip to these scored surfaces before pressing the pieces together firmly. You must then smooth the seam on both the inside and outside of the vessel to create a unified wall structure. This process is similar to how a welder fuses two metal beams together to create a stronger, singular support column.
To manage the assembly of your lidded jar, follow these essential steps to ensure structural success:
- Measure the diameter of your base section to ensure the middle section fits snugly without creating stress points.
- Score both connecting surfaces deeply to create a mechanical lock that keeps the wet clay pieces from sliding apart.
- Apply a consistent layer of slip to act as a glue, effectively bonding the clay particles across the seam.
- Compress the seam using a wooden rib to eliminate air pockets that could cause the vessel to explode.
Following these steps requires patience, as rushing the drying time or failing to compress the seams will lead to cracks. Once the parts are joined, you can refine the exterior surface to hide the seams and create a polished, professional finish. The goal is to make the transition between sections invisible to the eye, giving the illusion that the jar was thrown as one single, continuous piece. Mastery of this skill allows you to push the boundaries of your ceramic designs, enabling you to build vessels that are taller and more complex than your wheel alone would allow.
Successful assembly of complex ceramic vessels relies on precise timing and the careful integration of separate parts into a singular, unified form.
But this model of structural assembly breaks down when the clay sections have different moisture levels, creating uneven shrinkage rates that threaten to tear the vessel apart.