Part 2 (1/2)
With great care and much taste pieces can be pinched and welded together into delightful forms, best shown in the refinements of the Cha Noya pottery of j.a.pan. This pinching must be done carefully and above all sympathetically. To those that know or feel the possibilities of the clay it will respond readily. Much more taste and judgement is required in the making of a really satisfactory pinched shape, than is needed in forming one with coils. Square, polyhedral, or irregular shapes other than circular may be _stuck up_ or pieced together in the following manner: Upon a table nail two strips of wood one quarter of an inch thick, ten or twelve inches apart. Sprinkle between the strips with flint or fine sand and batter out some soft clay thereon. Sc.r.a.pe the surplus clay off with a straight-edge and then roll the clay between the strips flat with a rolling pin. Upon this thin slab mark out the sides, base, top, etc., of the shape to be built. Run a thin knife round each shape, but do not cut quite down to the table. Cut along the inside edge of each strip to allow the whole slab to contract evenly and allow it to toughen slightly.
Carefully remove and reverse the slab and separate the pieces, being careful not to distort the shapes in the process.
The shape must be stuck up before the pieces become brittle or too stiff to bend. Roughen each opposing edge and moisten with slip, that is, clay mixed with water to the consistency of thick cream.
Press the edges firmly together and weld well each joint with soft clay.
(Fig. 5.) This operation should be most thorough, as any weak joint will inevitably open when fired. Lids should be cut slightly larger than the shapes they have to fit and sandpapered true when dry. Sharp edges and angles should be smoothed with the fingers before the shape gets hard.
[Ill.u.s.tration: FIG. 5--”STICKING UP” FLAT-SIDED POT.]
The chief pitfall to avoid in this process is a hard wooden look. The ductile plastic qualities of the clay should be remembered and such additions as feet or handles should emphasize this important point.
Finally, the careful sympathetic craftsman, with infinite patience, by utilizing all three methods, can build vessels of almost any shape,--square, round, elliptical, banded, strapped, bossed, fluted, and embellished with handles, spouts, and feet. Ancient and mediaeval pottery is rich in such forms.
[Ill.u.s.tration: TOOLS FOR CLAY WORK.]
CHAPTER IV
MOULDING, CASTING, AND PRESSING
”Our soundes is good, Our shapes is neat, Its Davis cast us so compleat.”
--From an old bell at Stoke Rivers.
The casting process, employed so extensively in commercial work, is in its essence mechanical and therefore can never have the spontaneity or character of thrown work. To-day when the thrower and turner with hand and eye trained for good shapes is rare indeed, it is often the only method by which the student can obtain large shapes of high finish for painting or glazing in transparent colours.
In the process the shape is first designed and carefully drawn on paper, allowance being made for the shrinkage of the finished pot which may be as much as 1 in 6 with some kinds of slip. It should be refined in profile with no returns that may bind or hold in the mould when drying, yet it is obvious that simple shapes that can be built or thrown by the beginner are not suitable for casting.
[Ill.u.s.tration: FIG. 6--MANDREL, ROLLED IN PAPER.]
[Ill.u.s.tration: FIG. 7--”ONE PIECE” MOULD FOR BOWL--METHOD OF RELEASING ORIGINAL.]
The shape correctly drawn, a mandrel, a steel tapering to a point, the b.u.t.t wormed to screw on a lathe, and long enough to give some play at either end, is rolled in stout paper, gummed at the edges, as in Fig. 6.
This is removed and allowed to set, thus giving a paper sh.e.l.l just fitting the mandrel. Trim this square at the base and stick it upright by means of a piece of clay on a well-oiled portion of a table. Around this as a centre is fitted a roll of linoleum, oiled inside and secured with string, with all its joints caulked with clay. The inside diameter of this cylinder should be about 1/2” larger than the greatest diameter of the drawn shape. Enough superfine plaster to fill this is now mixed. To do this shake plaster by handfuls into a bowl of water until it appears to refuse more, pour off any surplus water, and stir with a wooden ladle or the hand, avoiding air bubbles.
[Ill.u.s.tration: FIG. 8--A TWO-PIECE MOULD.]
[Ill.u.s.tration: FIG. 9--POURING IN PLASTER.]
A little practice in casting plaster bats will give the experience necessary for mixing plaster. When well mixed and a slight thickening is perceptible, it is poured very carefully into the cylinder, the paper sh.e.l.l being kept upright in the centre. (Fig. 9.) In about 20 minutes the surface of the plaster will feel warm. It is now set and the linoleum is removed. The plaster cylinder, when dry, is fitted on the mandrel, and this screwed to the lathe head. Two or three chisels are now required.
(Fig. 10.) The rest on the lathe is clamped in a convenient position and a cutting chisel held as shown (Fig. 11), cutting edge up. The cylinder is revolved briskly as indicated by arrow, and the shape is roughly hollowed out. Proceed gradually until the shape begins to emerge, taking care not to cut too deeply. (Fig. 12.) Towards the finish use the calipers frequently to check the measurements. At top and bottom about 1/2” waste is left (Fig. 13 A), turned straight, the actual line of top and base being slightly grooved in the plaster. The form may be pretty accurately finished with the chisels and then nicely smoothed with sandpaper. For this process the rotary movement is reversed.
[Ill.u.s.tration: TURNING TOOL.]
[Ill.u.s.tration: FIG. 10--CHISEL POINTS.]
[Ill.u.s.tration: FIG. 11--POSITION OF TOOL.]
The shape is now removed from the lathe and is ready for moulding.