BUILDING A PIECE OF POTTERY
1. Making the First Coil
2. Testing the Outline
3. Continuing the Piece
Should the walls become weak and insecure from working them too rapidly, let them dry for a longer time, several hours or over night, before finishing. Test the shape constantly with the cardboard outline. When the jar is as high as the drawing, or even a quarter to half an inch higher, let it dry over night. It should then be smoothed with an oval steel tool, which has a saw-toothed edge (see Fig. 5), to take the worst unevenness off. The tool is bent to fit the shape of the jar and held at right angles with it, smoothing it with short strokes in different directions. This is done inside and out. The hollows are also filled in. To do this, wet the spot first with slip and fill in with clay as nearly the consistency of that in the jar as possible. The sides are then made perfectly even with the oval tool with smooth edges, holding it as the saw-toothed tool was held. When there are no hollows or ridges and the walls are about a quarter of an inch thick, the surface of the jar is smoothed with a damp sponge and polished with the fingers and thumb inside and out, taking care in handling it not to hold it by the edge, but rest it in the hollowed hand. Should it have become very dry, as it will in a comparatively short time in warm weather, so that it is light-gray in colour, it will be wise to smooth it with sandpaper instead of with the sponge, as in this state even a little water may cause it to crack. One cannot learn too soon, or have too often impressed upon one’s mind, the risk of adding wet clay to a piece of pottery that is much drier. The natural shrinkage which has already taken place in the dry clay will be repeated in the wet, and, as it shrinks, it will crack the drier clay. Cracks in clay are of two kinds—those caused by shrinkage of the unbaked or green clay, and those that come from cooling too rapidly in the biscuit or baked clay. The former can usually be mended satisfactorily, but for the latter there is no remedy; the piece is spoiled.
To mend a crack in clay that is only partially dry, put a little slip into the crack and then work in, with a modelling tool, clay of the consistency of the piece. If, after drying longer, the piece cracks again—a long, deep crack, that goes through to the inside—there is no way to mend it except by cutting the clay out on either side for quite a space beyond the crack, brushing both sides with slip, and filling in with clay as nearly as possible the consistency of the piece. This is pressed in in small bits, little by little, until the gap is filled. If it should crack again in small, short places, fill them with dry, powdered clay, pressed in and moulded with a steel tool.
In case of the piece cracking when it is bone dry—that is, after it has dried for several days and is pale-gray in colour—grind some pieces of baked clay to a fine powder, add enough water to make a soft, yellow paste, and fill the cracks with it.
The edge of the jar is cut as even as possible with a tool, and then made perfectly true by the following method: A little water is poured on a ground-glass slab, and the jar, held bottom up, is moved firmly but rapidly round and round on the wet surface, and then quickly taken up (by sliding it off at the edge of the slab) before it clings to the glass. The bottom must now be finished. The jar is first placed bottom up on a slab or table, then a circle is drawn with a pencil at about half an inch from the edge of the bottom. This is outlined with the pointed steel tool, and the bottom within the circle is evenly and carefully cut out with strokes of the oval, smooth-edged tool, so that the outside ring shall form a ridge not over one-sixteenth of an inch above the depressed interior of the circle. The potter now cuts his initial or mark, which is made in as simple lines as possible, into the bottom with firm, deep strokes. If the jar is not very dry, a wooden modelling tool may be used for this. Otherwise, the pointed steel tool is chosen. Care should be taken not to cut under the edge in making these incised lines. The edges should instead be bevelled, so that, when the glaze is put on, it will flow more freely over them.
If possible, this jar, being large, should be fired in the biscuit—that is, before it is glazed, and then again after it has been glazed; unless one is obliged to send it a long distance to be fired, so that more than one firing is impracticable, in which case it must, of course, be glazed on the unbaked clay.
A pale green glaze (see directions in Chapter V.) will complete it.
In packing to send pieces to a far-off kiln by express, use a wooden box, and, after lining it with newspaper, wrap the pieces in soft paper, and pack them carefully in sawdust.