Slab method for ceramics
The slab method is an essential technique for working with plastic clay. Objects can be constructed simply and with a minimum of effort. In this method, plastic clay is rolled to a certain thickness, and pieces are cut out according to selected patterns and are then joined with thick pasting slip and coil "snakes." The pieces or "slabs" may be employed flat, or may be curved prior to slip pasting.
The variety of objects that can be made by this method is infinite and gives a large field for the play of imagination. Simple items, with a modernistic appearance, employing flat or single curved surfaces are most attractive.
Items made by this method can be further varied by the addition of flower ornaments, coil method pieces, or with a certain amount of hand modelling. Also handles or other pieces made by the slab method can be slip pasted to moulded objects, or used as parts of objects constructed by other methods. Several illustrations are included to indicate the combinations possible with pieces made by this method and those of other methods.
In the parts of the following lesson we shall discover the details of working by this method.
Part I. Making a Lidded Box
Procedure: First we will prepare the tools with which we are going to work. Fasten together with screws the two 6-inch lengths of wood at right angles along their length.
While the pieces are curing on the plaster bat, roll a snake of clay about 1/8 inch in diameter. When rolled, place this snake under a moist cloth.
We shall now assemble the box. Place the base piece on the breadboard. Apply slip paste along one long edge of the base piece. Apply slip paste along the lower 1/4 inch of one side piece. Place the side piece vertically on the breadboard against the base piece. Put the cigar box on the other side of the side piece to brace and keep it erect (Fig. 9B). Cut a 3 1/2 inch length of 1/8 inch moist snake. Apply slip plentifully and then place the snake on the inside angle formed by the base and side pieces (Fig. 9C). Now with the curved orange stick end, wedge this snake smoothly into the angle. Press gently so as not to separate the base and side pieces (Fig. 9D). The cigar box on the outside assists in keeping the pieces from separating, as well as supporting and retaining the shape of the side piece.
Place the upper and lower top pieces on the breadboard. With the point of the pen knife score the surface of the lower top piece by crisscrossing it to a depth of 1/32 inch. Also score the surface of the upper top piece leaving a smooth margin of /4 inch on all edges (Fig. 10C). Apply thick slip paste to both scored areas. Now carefully fit the lower top piece to the upper top piece, so that the scored areas are together and a margin of 1/4 inch remains on all sides of the upper piece (Fig. 10D). With the upper top piece below set the assembly out to dry.
Explanation of techniques: The oilcloth is moistened on the shiny side before placing that side against the breadboard so that it will adhere to the breadboard, and thus will not slip while clay is being rolled on the cloth.
Clay pieces are placed on the plaster bat because plaster draws out the moisture from clay. However, the pieces are turned over frequently so that the moisture will be drawn out of both surfaces equally. As clay cures, it stiffens. However, at no time should the clay be so dry that it begins to show lighter dry portions; it should always have the appearance of being moist while it is being worked.
Thick slip should be applied plentifully at the joints. Do not worry if slip runs out of the joints when the pieces are fitted together. This excess can be smoothed with the moistened finger afterward.
When ornaments or handles are to be slip pasted to larger objects they should always be more moist than the large objects. Drier clay always draws moisture from wetter clay. If the handle or ornament were more dry than the larger object, they would draw moisture from the larger object and cause the surface of the larger object to warp in the vicinity of the handle or ornament. The handle, while more moist, has, over all, less water to lose and thus affects the larger object much less. Further, a very slight warpage of the handle or ornament would be scarcely noticeable.
The purpose of scoring the surfaces to be
slip pasted together is to give a better "bite" to the slip
and cause better adhesion of the pieces.
If it is desired to vary the texture of the clay surface, before the model pieces are removed from the breadboard, a piece of burlap cloth or other wide woven material can be placed on the clay, and the rolling pin passed over the top of the cloth. The cloth is then peeled off. The clay surface will take on the appearance of the cloth texture. Very striking and pleasing effects can be thus obtained.
If thinner slabs of clay are desired, thinner sticks of wood are used as parallel thickness guides for the rolling pin at the time the clay slab is being rolled out on the oilcloth and breadboard.
Part 11. Making a circular mug
Materials: Same as in part I, this lesson.
Procedure: Make the paper patterns (Fig. 12A). Wedge and roll out a slab of clay 1/4 inch thick. Place the patterns on the clay slab, and cut out clay pieces, as instructed in part I, this lesson. With the slant portion of a school type of ruler placed on the parallel sticks as a guide, place the pen knife against the slant surface of the ruler and cut the clay of the side piece along the edge at a slant (Fig. 12B). Turn the piece upside down and cut the opposite edge with the same slant. Let the cut-out pieces cure on the plaster bat 10 minutes on each side.
Hints: As a matter of regular procedure, whenever slab pieces are slip pasted together to form an angle, a thin snake of clay is always placed in the angle after applying slip paste. This snake is wedged in the angle to both sides to seal the joint and support both pieces. If the snake is difficult to get to for wedging into the angle, a tool with a small ball-shaped end (a ball 1/8 inch or 3/16 inch in diameter) may be used for the wedging.
Surface imperfections (except holes) should seldom be corrected while the clay is in plastic or "bone dry" state. Fill any small holes with soft clay and smooth them over with a moist finger before the clay is dry. Pimples and bumps are better smoothed off with sandpaper after the object has been fired to bisque.
Sharp edges are always sandpapered and slightly rounded in bisque, because the glaze sticks to a sharp edge with difficulty and may run off when fired, leaving the edge itself unglazed or uncoloured.
The handles should always be light in weight, so that, during drying, they will not pull and distort the wall of the object to which they are pasted.
Part III. Making a ceramic bow knot
Materials: Same as in part I, this lesson.
Comments: This slab type of ornamentation is pretty and attractive, yet easy to construct. It will beautify any kind of ceramic object to which it is applied. This part of the lesson is devoted solely to this item.
Procedure: Cut out paper patterns twice the size of those shown in Fig. 13.
The secret of making the bow is the wetting of part A along the dotted lines before folding, otherwise the edge will crack when folding over or when fired. This bow knot may be made in different sizes, by reducing or increasing the pattern proportionately.
Part IV. General techniques in making slab method objects
Once the general procedure for making ceramic objects by the slab method and the several points indicated in this part of the lesson are mastered, it is a simple matter to create new objects of almost any type. The examples shown indicate the variety of objects and the special points to be considered in each.
In creating a new object it is desirable to draw and cut out the design or pattern in cardboard for each individual piece; and then assemble the paper patterns with scotch tape to see that the clay pieces cut from these patterns later will fit together properly. The cardboard patterns should always fit before cutting clay pieces from them.
The clay may be rolled to varying thicknesses
as desired. The larger the object, the thicker the slab. In large pieces,
it may be desirable to reinforce slabs with ribs of clay to reduce warping
when the object dries, or is fired. This ribbing may be seen in several
of the illustrations.
Lines where pieces join are smoothed with the moistened finger to conceal them.
Slab pieces may be modelled to some degree with the hands or modelling tools to give variation to the surface. This is not always necessary, as a large part of the decoration of the object will take place when it is glazed and painted with various colour designs. Do not feel that the object is too plain, and therefore requires some kind of plastic decoration; the numerous types of glaze and painting decoration will add greatly to its attractiveness. Lessons X and XI will indicate how to decorate an object even though it is simple and plain-for example, a square flat tile piece.
You should decide upon the size of the final object and cut your cardboard patterns in proportion. This is excellent practice in learning to create new designs.
Do not attempt to smooth the pieces too much while in the moist state. After the object is fired to bisque, round the edges and smooth any imperfections with sandpaper.
Towel ring and support: The procedures given in the previous parts of this lesson cover the making of these objects except the making of the holes where the support is to be screwed into the wall. These holes should be cut out with a hollow metal tube, such as a curtain rod, while the back piece is still plastic. This assembly will look very attractive when fired in opaque mat glaze colour.
Cigarette tray: The curved portion of the tray may be formed halfway around the rolling pin or other cylindrical object. Very thin snakes (1/16 inch in diameter) should be wedged in the angle formed by the supports and the curved surface.
Ash trays: In cutting the semi-cylinder hollow where the cigarette is to rest, use a curved knife similar to one used for coring apples, or a half-round wood chisel.
Hot roll dish: Cut out the cardboard pattern for this dish and fit it together to make sure that it is correct in size and shape. After the clay pieces are assembled, the side pieces may be flared out by hand to vary the shape. Clay balls which are drier than the sides may be placed against the sides to support them while drying and removed when the assembly is almost "bone dry."
Book-end: There are any number of book-end designs which can be made. The base is usually thicker than the vertical side to give weight to the bottom. However, if a metal figurine is plastic-cemented to the base after the book-end is glaze-fired, it will add more desirable weight for the support of books; the ceramic book-end itself is somewhat light in weight. At no place should the clay be more than 1 inch thick.