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.

Lesson III

Part I. Making a Lidded Box

Materials:

  • The same materials as in Lesson II plus:
  • 2 pieces of wood 1 foot long, 1 inch wide, and 1/4 inch thick
  • A cigar box filled with sand
  • 2 pieces of wood, each 6 inches long, 2 inches wide, and 1/2 inch thick Wood screws
  • Several pieces of triple zero sandpaper
  • 1 plaster bat (see lesson VIII)
  • A razor blade
  • Paper and scissors

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.

Fig 8

With the razor blade shape the end of one orange stick to a smooth curve. Polish the curve to smoothness with sandpaper. A boxwood curved modelling tool may be used instead of the shaped orange stick.

Measure and draw on paper the pattern of the box pieces (Fig. 8). Cut out these paper patterns with scissors. Wet the shiny side of one piece of oilcloth and place this side on the breadboard. The dull side will be uppermost.

Fig 9

Wedge a handful of clay and place it on the oilcloth. Flatten the clay with the palms of the hands until it is about 1/2 inch thick. Now place the 1/4 inch sticks parallel on either side of the clay. With the rolling pin, roll the clay to a thickness of 1/4 inch, working the rolling pin from the centre outward. The sticks will determine the proper thickness (Fig. 9A). Place the paper patterns on the rolled clay. With the pen knife held vertically, cut out the clay pieces. Remove the excess clay by cutting and peeling it away, leaving the patterned pieces on the oilcloth. Carefully remove the paper patterns from the "model" pieces.

Now remove the model pieces. Place one hand under the oilcloth and lift up under each piece in turn. Turn the cloth over so that each piece will fall into the other hand. Carry these pieces to the plaster bat and lay them on the surface of the bat. After 10 minutes, turn the pieces over on the bat to remain for another 10 minutes.

These pieces are placed on the plaster bat so that they will dry and stiffen slightly. Turning them over insures uniform drying on both sides and prevents warping of the pieces as they dry. This process of plaster bat drying is known as "curing."

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.

Fig 10

Before putting on the end piece, slip paste the base and side of the side piece where the end piece is to touch, and slip paste the end piece along the corresponding areas. Fit the end piece in place. Cut two lengths of the snake, 2 1/4 inches and 2 1/2 inches, respectively. Apply slip copiously and then place these snakes in the angles formed by the end and side pieces, and the end and base pieces (Fig. 10A) .

Place the cigar box behind the end piece when wedging the snake to it and the base piece. Now place the right angle formed by the two pieces of wood (made at the beginning of this lesson) against the outside angle of the end and side pieces. This angle will support the corner when wedging the snake. It also preserves the corner and prevents separation (Fig. 10B).

The opposite side and end are slip pasted and wedged in turn and in like manner. Pass the moist finger on the outside of the joints between the side and end pieces to smooth and conceal the joint lines.
Set out the assembly to dry.
We shall now make the lid of the box.

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.

Fig 11

If it is desired to place a flower ornament or handle on the top piece, this ornament can be slip pasted to the top of the upper top piece (Figs. 11B and C). The ornament or handle should always be more moist than the lid.

Ordinarily the lid would be set upside down to dry. However, if an ornament or handle is put on the lid, take the following action. Roll a number of clay balls 1/4 inch in diameter and place them under the extending lips of the upper top piece. Paste the ornament or handle to the top piece. Permit these balls to remain under the lips until the lid is almost "bone dry." The purpose of the balls is to prevent the lips of the upper top piece from sagging while it is still moist (Fig. 11D). These clay balls will not normally adhere to the upper top piece and can be removed easily.

After the box is bisque fired, the edges of the box should be rounded slightly with sandpaper. All imperfections on the surfaces may be smoothed with sandpaper. The edges of the lower top piece may be carefully scraped with a knife to insure that the piece fits into the box. Allow about 1/16-inch all-around play between the lower top piece and the box; the fit should be loose, not tight.

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.
Hints: When the objects are set out to dry, if any holes are noted in the clay, these can be filled in with soft clay and smoothed over with the moist finger.

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.

Fig 12

Now pick up the side piece and, with the rolling pin or a perfectly cylindrical glass as a guide, curve the side piece around to form a perfect cylinder. The slant portions should overlap (Fig. 12C). Apply thick slip to each of the slant surfaces and wedge them together. Smooth the joint line with the moist finger. The shape of the cylinder can be carefully corrected with the palms of both hands.

Check to see that the base will fit exactly inside the lower end of the clay cylinder. It may be necessary to trim the base circle to smaller size with the pen knife to make it fit. Apply pasting slip to the inside of the cylinder at the bottom and around the edge of the base. Place the cylinder over the base piece.

Roll a 1/8 inch snake and cut it about 10 inches in length. Place it in a circle around in the inside angle of the cylinder and base. Carefully wedge it into the angle, as was done in the box angles in part I of this lesson.

Now taper the ends of the handle by pressing gently with the fingers. Shape the handle to the curve indicated in Fig. 12D. The handle is slip pasted against the joint of the side piece (cylinder). Apply slip to the inside of the tapered ends of the handle and to the cylinder where they are to join. Gently wedge the handle on with the finger-using the glass on the inside of the cylinder as a support.

Set the mug out to dry. After the mug is bisque fired, sandpaper the sharp edges at the bottom and along the handle. Round the lip of the mug with sandpaper. Smooth all imperfections.

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.

Fig 13

Roll out a slab 1/16 inch thick. Place the patterns on the clay and cut out the clay, as instructed in previous parts of this lesson. Smooth the oilcloth markings with the moist finger.

Refer to Fig. 13. Apply pasting slip to one end of part B. Place the centre of part A over the pasted end of part B. Now, with the finger, apply moisture to part A along the dotted lines. Fold over the outer parts of part A until the ends touch (Fig. 13E). Apply slip to the junction. Fold part B up, over, and back around part A (Fig. 13F).

Apply slip to the larger ceramic piece where the bow is to be fastened. Apply slip to the narrow inside ends of parts C and D and place them on the slip of the larger ceramic piece, leaving a gap wide enough for part B of the bow to fit in between. Apply slip to the lower side of part B, and gently wedge the bow into place. Let the ornament rest for 10 minutes to dry partially.

Now with the help of the orange stick or modelling tool, curl the parts C and D so that they will look natural (Fig. 13G). Apply slip at the outer portions where they now touch the larger ceramic piece.

Press indentations in the top of the bow and the loops with the tool to give an appearance of natural folding or creasing of a bow knot (Fig. 13G). Do not cut the clay when indenting; merely press in. A cut may crack on firing.

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.
Remember that all angles are slip pasted and wedged with a thin snake, for sealing and reinforcement. When wedging an angle, back up the outside of the slab pieces or support the angle with a block of wood or other solid object to prevent the opening of the joint. Do not exert much pressure to the wedging tools in wedging.

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.

Additional Projects

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.

Fig 14

Modernistic triangular pitcher: The pattern in cardboard must be made and assembled before this object is attempted in clay, thus insuring that the pieces will fit. If the pitcher is made in a large size (one quart size or greater) ribbing should be slip pasted on the outside of the sides to prevent warping. The ribbing shown on the illustration is about 1/8 inch thick and is in the form of a decorative design. Cut out the ribbing from a 1/8 inch slab. After bisque firing, the ribbing may be painted in contrasting glaze colour to the colour on the main surface of the pitcher.
The spout should be well wedged together at the joint and flared out slightly with the fingers. Where the sides come together, cut them and taper them inward, slip paste, and wedge on the outside to insure a closed joint. Wedge the snakes in the inside angles of the sides before the base is attached. Glaze the pitcher on the inside to hold water.

Retaining rim: In pitchers or other objects with a lid, it is necessary to provide a rim to keep the lid in place. If the lid is smaller than the lower object on which it fits, the rim is put in the lower object. If the lid is equal to or larger than the lower part, the rim is placed on the under side of the lid. Several methods are illustrated (Fig. 14). This rim may be part of a coil, or pieces cut from a slab. The slab in the lower part of the lid in part I, this lesson, was used not only to add weight to the lid, but also to retain the lid in the proper place on the box.


Ceramics:
  • Index
  • Coil method
  • Decoration
  • Glaze decoration
  • Glossary
  • Hand pressing
  • Kiln & firing
  • Mould making
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  • Potters wheel
  • Slab method
  • Slip casting

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