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   TECHNICAL NOTES

Hand-building  |  Hollowing the clay figure  |  Photo silk-screening  |  Silk-screening on nonplanar surfaces Trimming the foot


HOLLOWING THE CLAY FIGURE

 

Overview  |  Slicing the figure  |  Separating the segments  |  Scooping the interior  |  Reconstructing the work  | Repairing the seam

 

  • Kiln firing is responsible for damage to ceramic figures that have not been properly prepared for exposure to the very high temperatures of the firing process.  Inadequate drying and trapped air within the clay are major contributors to such kiln accidents.
  • To avoid them, it is advantageous to hollow out the interior of a clay work. Making the wall consistently uniform in thickness faciitates the drying process and considerably reduces the risks that occur during the firing. To emphasize the point, the novice ceramacist can guarantee damage if this process is not undertaken.
  • For teapot construction, the hollowing process does double duty in providing the necessary cavity for a functional vessel.
  • The hollowing process consists of several steps: Slicing the clay figure into two segments to gain access to the interior; separating the segments; excavating the interior by scooping out the excess clay until the remaining walls are uniformly thick; reconstructing the piece by putting the two segments together again; and repairing the seam to make it strongly adherent, not vulnerable to cracking, smooth and invisible to the eye.

 

SLICING THE FIGURE

 

Incision is begun in areas that will avoid damaging delicate structures.
  • The optimal time for hollowing a clay figure is before it has become completely dry, that is, while it is in the leather-hard state. More specifically, it is best done while kthe clay is still wet enough to work easily, but not so dry as to crack or crumble during the cutting and separating steps.
  • Equally important is choosing a time early in the construction process before detail work has been undertaken. This is solid practical advice that wil help avert the frustration that will come from unavoidably harming those delicate areas during the ensuing hollowing-out step.

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Tissue knife being used to expose inner clay core of sculpted head.

  • Head section is dealt with separately because its cavity will be separated from the body cavity by a plane of clay left intact at the neck. This is necessary because the fluid level in the teapot body cavity cannot be higher than the lid opening, which in this piece will be at the back of the neck as part of the hair clasp (see Be-you-tea-ful Dreamer).

  • A tissue knife is used to cut vertically straight down into an area of the sculpted head that is as yet not fully developed. Another incision is made horizontally at the neck level to expose the inner clay core.

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SEPARATING THE SEGMENTS

Separating the segments is begun.

  • Give some thought in advance to planning where to slice the piece to minimize potential harm to those areas that contain fine details of construction, such as projections and other delicate features.
  • Slicing the object can be done with a two-handled cutting wire, a fettling knife or, as in this case, a long flat sharp tissue knife. Images here are of the entire process being done on the piece called Hot Wet Tea-Shirt.

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The sliced face segment is separated from the back of the head.

  • The face component is separated from the head to expose the clay core that will be scooped out in the hollowing process to follow.

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SCOOPING THE INTERIOR

Scooping away excess inner clay.

  • After slicing the work into two or more sections, separate them slowly and carefully so as not to inflict any damage on the still-soft and vulnerable clay of the outer walls.
  • The individual segments are carefully separated from each other, as shown here.
  • Scoop out the interior clay using a ribbon or wire loop tool. While stripping away the moist clay to make the wall a uniform thickness, be particularly careful to avoid breaking through (that is, creating a button-hole) to the external surface.
  • If this occurs, repair it at once by moistenng the button hole with water or slip and applying bits of clay from the inside, smoothing it on the outside with some water.
  • Aim to make the wall between 1/4 and 1/2 inch thick throughout. Be especially alert to possible air pockets. Consider using the prongs of a fork to make a series of holes in the inner clay surface half-way through its thickness to help ensure against leaving undetected air bubbles.
  • Keep your free hand outside of the piece to judge the wall thickness during the scooping process.
  • Use a small loop to hollow out the clay of all delicate projecting areas of the piece.

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The face segment is marked to designate where inner clay will be scooped away to form the inner cavity and make the wall uniformly thick.

  • The face segment is inscribed with a needle point tool to demarcate the desired thickness of the wall that will remain after the inner clay core is hollowed out by scooping.

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The core clay is scooped out of the face segment by a ribbon tool.The sequence of scooping the back of the head segment is shown.

  • The excess clay of the face and head segments is scooped out by means of a ribbon tool, leaving a cavity unconnected to the main cavity of the piece and an outer wall of uniform thickness. To provide venting of the newly formed cavity and thereby prevent a kiln accident, a small opening is made in the ear canal of the piece.

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RECONSTRUCTING THE WORK

The edges to be joined are scored with a serrated edge rib too. to roughen them.

The edges to be joined are scored to roughen them and wetted with slip to secure the join.

  • A serrated edge rib tool is used here to score the edges of the cut segments that will be joined together. Roughening them helps to secure the seam. Scoring can be also be done with a needle point tool.

  • After scoring, the edges are brushed with water or preferably, as in this case, with slip which will act as a glue to further ensure the integrity of the seam. This is the score and slip method for joining clay segments.

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The component parts are reassembled.

The head section is reassembled; the rough seam is shown before smoothing.

  • After all cut edges have been scored and slipped , the work is ready to be reassembled.
  • The corresponding hollowed-out segments are placed together, aligning the cut edges precisely.
  • Firm pressure is applied to dispel any trapped air in the seam and ensure close, firm, tight contact.

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REPAIRING THE SEAMS

The seams are reenforced and smoothed so they become invisible.

  • The seams require reenforcement to prevent cracking during subsequent firing and to smooth the surface so they are not visible.
  • This is achieved by shallowly scooping out the external edge of the seams all the way around the clay figure.
  • Wet the channel made along the seams by brushing with water or slip and refilling with pieces of soft clay. Then smooth them with a moist finger or flat wooden tool to blend in with the surrounding surface. The seam, when reenforced in this way, will prove strong and resistant to damage during firing and yet be invisible to the examining eye.

 


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