This Project Will Help Students

  • Throw a closed form on the wheel
  • Trim a closed form using a chuck to support it, a skill also needed
    for trimming narrow necked bottles, and forms with fragile or uneven
    rims
  • Create a tight fitting lid from part of the closed form.
  • Analyze and address problems with throwing, trimming and
    craftsmanship after cutting the piece apart and reassembling it. For
    example, is the top of the form too thick, do you see excessive shifts
    in wall thickness, evidence of twisting in the clay?


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No Measure Lids


Throwing
Center approximately one pound of clay (figure 1). More could be used for larger round forms, but I prefer to keep these containers small and jewel-like.
Open the clay and leave 3/8 inch of clay on the bottom for a trimmed foot (figure 2).
Slightly curve the bottom to establish the contour of the entire form. Exert more pressure with the outside hand and throw a slight conical shape (figure 3). This makes the form much easier to close later. Keep the rim open only wide enough to get a couple of fingers inside.
Leave a thick bead of clay at the rim. A thicker rim is beneficial both for closing the form and creating a knob. Once the height is established and the clay wall thinned sufficiently,
round the form by exerting more pressure from the inside (figure 4).
Maintain some support with the outside hand so the form remains
centered and doesn’t twist. If the base is too thin or over extended
the form could collapse later. A lot of torque is placed on the form
when closing the rim and fashioning the knob.

 

Push through the thick bead of clay at the rim to close the form
(figure 5). Keep a finger or two inside the form to support the clay
wall while you close. If your fingers are too big, try using a pencil
or handle of a tool. To facilitate drying and deter S-cracks, use a sponge to remove any
water that might remain in the bottom of the form before you close it
completely.

The opening eventually becomes small enough to squeeze shut completely
(figure 6). A short column of clay should be preserved from the rim to
aid this motion. Keep your fingers very wet as you compress the rim
from both sides to prevent the rim from twisting.
Fashion a knob from the excess clay by applying pressure from the top and support from the side (figure 7). Undercut the knob slightly using the rounded end of a tool for a more
dramatic profile. This also makes the knob easier to grasp and hold on
to once it has been glazed and fired.
Use a soft flexible rib to refine the overall form (figure 9). Because
the form is closed, air trapped inside acts as a support, keeping the
form from collapsing even under rather aggressive shaping. Run a cutoff
wire underneath the form to release it from the wheelhead or bat and
move the piece from the wheel to a ware board to dry. Poke a small hole in the form with a needle tool to allow the air to escape while the piece dries and begins to shrink.
Trimming
At the leather-hard stage, place the piece in a bisque-fired chuck (figure 10). Chucks are useful for trimming forms that are uneven or fragile, or cannot be turned upside down on the wheel. Thrown chucks may be used in either the green or bisque state. Since clay doesn’t stick well to bisqueware, soak the bisqued chuck in water for several minutes before using to make the clay wads hold more securely.
To level the piece, hold a needle tool steady as it revolves (figure 11). The needle marks the highest spot. Shift the piece in the chuck until it is level and the needle makes an even mark around the bottom. Alternately, use a bubble or spirit level to check the bottom, placing it across the center of the foot in various directions to be sure that all sides of are level.
Secure the form to the chuck with wads of soft clay (figure 12). Apply only enough pressure to stick the wads to both the piece and the chuck. The piece should not shift in the chuck. Check for level again before beginning to trim. Center the chuck by holding the needle tool to the side of the form to
mark the side that protrudes farthest from the center. Align the mark
so that it faces you and push the chuck away from you slightly. Repeat
this until an even mark is made around the piece. Use additional wads of soft clay to secure the chuck to the wheel head. Again, be careful not to push the chuck off center as you
do this.
As the interior of the piece cannot be seen at this point, it’s
important to visualize the inner curve you established while opening
and throwing the form so that you’ll know how much to trim away from
the bottom and the foot. Trim the bottom of the form, creating a foot ring (figure 13). Mirror the exterior contour off of the visualized memory of the interior contour. Tapping the form and comparing the sounds produced at
various points indicates if the thickness of the clay wall is
consistent. Trim the bottom of the form, creating a foot ring (figure 14). Mirror the exterior contour off of the visualized memory of the interior
contour. Tapping the form and comparing the sounds produced at various
points indicates if the thickness of the clay wall is consistent.
Turn the form right side up in the chuck. Level as before and use a
needle tool to score two faint concentric circles (figure 15). These
circles are a guide for cutting out the lid, all of the undulations or
curves that you design into it will need to fit between the two lines.
Think of them as guidelines to facilitate both the design of the lid’s
and pot rim’s shapes. So, carefully consider the placement of these
two concentric circles in terms of visual proportions and adequate
access to the interior. Placing the lines further down on the form
creates a wider opening, but lessens the overall volume of the form’s
storage capacity. Placing them higher up, or closer to the knob,
creates more volume within the form, but narrows the opening and can
limit access to the interior. Place the lines so that they make sense
visually as well as with the intended function.
Cutting
Rather than cutting a circular lid that slides around on the form because it has no flange to help it register, draw a modified, notched lid. Use a round plastic form to trace semicircles between your two guide lines, creating the rounded notches (figure 16). The smaller, or top concentric circle establishes a uniform height for each of the arcs or semicircles that create the notches. The lines that create the arcs along with the larger, or bottom, circle determine where the lid will be cut from the base.

Looking down on the lid from the top (figure 17), trace the two rounded
arcs on opposite sides of the form, at 3 and 9 O’clock respectively.
Place a third arc or semicircle between the other two at 6 O’clock. The
notches are located at 90? intervals around the circumference of the
circle to prevent the lid from slipping either right to left or front
to back. Two notches would be sufficient, but add a third to visually
balance the composition or shape of the lid. Add more notches of
varying sizes and shapes if desired. Remember, however, the more
complex the pattern, the more difficult it becomes for the user to
orient and replace the lid during use.

Holding a thin knife blade at a 45? angle, cut through the lid following your guide lines to separate it from the form (figure 18). The cut runs along the larger, or bottom circle, and follows each of the three arcs. Once cut, the notches in the lid create a proper seat and prevent sliding. Cutting at a 45° angle provides enough of a seat on the rim to support the lid and ensure that the lid does not slide down into the pot. If the cut was made straight into the clay, it is likely that this would happen. The lid fits perfectly every time, even without measurements and calipers.

Smooth unwanted score lines, crumbs and sharp edges or corners with a
wet finger or sponge. These areas tend to trap glaze, even when waxed
over, and these droplets of glaze can be enough to fuse the lid shut
during firing.

 

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