Ceramic decoration howto

General: In the dawn of time, the first evidences of clay ware made by ancient man indicate simultaneously both his impulse to make useful pots and bowls and to beautify these crude utensils. The temptation to place a marking or design on the very impressionable soft clay before firing can be readily appreciated. It is thus that we note the crude marking, painting, and plastic decorative effects on ceramic objects among the prehistoric peoples, in ancient Europe, Egypt, Mesopotamia, and China, of earlier than 5000 B. C.

At first, ornamentation took the form of scratching or "incising" the surface of the object. Incising means literally "to cut into," and was performed possibly by a sharpened wooden stick, a stone knife, or bone instrument. The clay was also impressed by wrapping fibre or rope around the plastic surface and giving it a characteristic effect which is often found in ancient pieces.

It was but a step further to fill in the incised design with clay of another colour for contrast. This led in logical sequence to the painting of clay surfaces with clay slips of other colours-in other words, slip painting!

There is evidence to indicate that painted clay pottery was created prior to the Great Flood of biblical times; this painting included designs of several different colours. Incidentally, decorative figurines which had no practical utility were noted during this period. As time progressed and accidents of discovery took place, the use and application of glazes came into being.

Thus, all the basic methods of ceramic decoration were in existence long before man recorded the chronicle of history by the written word.

Forms of ceramic decoration

From the above and in previous pages, ceramic decoration takes two general forms-namely, plastic decoration, which is akin to sculpture; and surface colouring and finish, which is akin to painting.

The plastic form of ceramic decoration is usually accomplished while the clay is pliable. If you bear in mind that the moment a pottery object ceases to be purely functional, such as a plain cup, bowl, or pot, and you change its shape by any means to make it more pleasing to the eye, you have introduced a form of plastic decoration. This form includes the physical shaping of the object itself, incising, impressing, embossing, or adding clay ornamentation (ceramic flowers, etc.).

The painting form of decoration pertains to surface colouring and includes slip painting, underglaze, glaze, and overglaze types. The application of these colouring materials also affects the surface "feel" or texture of the object. This surface "feel" is referred to as the "tactile" effect. It is for this reason that we combine the colour and tactile qualities as one. In applying the painting form of decoration we appeal both to the eye and to the sense of touch.

The plastic form and painting form are invariably combined in ceramic decoration. In the following paragraphs, we shall discuss common colour and tactile effects. Having discussed the basic and more common types of plastic decoration in previous parts of this site, we shall not go into them further.

Colour and texture

The clay object may be coloured by any of the several methods; engobe, glaze, underglaze, overglaze, and lusters. The characteristics, texture, methods of application, and effects will be discussed in that sequence.

Engobe

Engobes are clay slips which are naturally or artificially coloured. When engobe is applied to the clay object while the object is "green" (unfired), we have, in effect, put a thin coating of coloured clay upon the clay "body" of the object. The engobe is applied to the "green" ware, and it is necessary to fire the object only once to "mature" both the body and engobe to bisque.

Note: The process of firing clays and glazes to their proper temperature is called "maturing."

Engobes can be purchased in natural colours in dry condition and converted to slips by the addition of water. These natural engobes can be blended with other colours, to almost any desired shade. However, the engobe can be purchased in dry state, already blended, in which case it is only necessary to specify the colour and mix the dry clay with water.

The engobe may be applied to the clay object when the object is leather hard or "bone dry." Engobe is applied with a camel's hair brush when a fine design is to be painted on the clay object. If the entire object is to be covered with engobe, it may be covered by painting with a large paint brush, by dipping the object in a pot of engobe, by pouring engobe from a bowl over the object, or by spraying on with a spray gun. In covering a plate a wide paint brush is usually used. A second coat of engobe is never applied until the first coat is completely dried. When a plate is to be covered with engobe, the second coat is always applied at right angles to the direction of the first coat, to permit both coats to adhere better to the body of the object.

Until the discovery of glazes, practically all painting of clay was done with engobes. With engobes therefore, many ancient Egyptian, Greek, Etruscan, Chinese, American Indian, and other antique or primitive types of ware were made which may be reproduced or imitated with identical engobe techniques.

Upon firing, the engobe surface will have the tactile quality of bisque. However, in time, the engobe surface is easily marked and may be rubbed off with handling. A transparent glaze therefore should be fired over the bisque in a second firing to prevent this rubbing off of the engobe.

Engobe techniques

There are several special techniques in using engobes which are quite popular today. These were employed in making Pennsylvania Dutch pottery, which is characterized by the use of engobe.

Pennsylvania Dutch pottery appeared in this country with the migration of these people from Europe to the new world at the invitation of William Penn in the seventeenth century. Their potters used characteristic designs in decorating ceramic objects, each of which is supposed to have particular significance.

They usually used red clay as the body, and employed other available clays in making their engobes. Their designs are not crude, and they have a freedom of movement, which, when mastered, gives quite delightful and colourful effects.

Slip painting should be employed for pattern designs and not for detail or realistic painting. Fine details cannot be easily drawn with engobe; subtle variations in tone and hue are better accomplished with underglaze and overglaze colours.

In this lesson we shall illustrate the techniques used. If you desire to make authentic reproduction, you should research in museums or books on Pennsylvania Dutch pottery and obtain the actual designs.

Lesson X. Decorating plates

Part I. Slip painting materials:

  • Red clay in plastic form, low firing
  • White, yellow, blue, green and black engobes purchased in dry state 6 camel's hair brushes
  • 6 small wide-mouth bowls
  • A boxwood or bone scratching tool Pencil and paper
  • A piece of thick cardboard

Comments: In this part of the lesson we shall first make a plate by the press method, permit it to become bone-dry, and then paint on a design in engobe.

Procedure: With the wedged red clay, roll and press three plates about 10 inches in diameter each, as indicated in lesson V. Let each plate become "bone-dry," and sandpaper each to smoothness. We shall use each plate to illustrate each technique.

Draw a 10-inch circle on paper with the pencil. Draw the desired design of the plate in the circle. Determine the colours you intend to use for each part of the design. A suggested design and colour scheme is illustrated in Fig. 36A.

Now mix each engobe to a fluid slip by adding the dry engobe to a small amount of water. Each slip is prepared in a separate small bowl. Use a different camel's hair brush for each colour. Test the consistency of the engobe by brushing it across a piece of cardboard to see if the slip runs freely and smoothly. The white slip will be quite thick, whereas the other slips will be thinner; the consistency depends on the material in the colour, and practice will indicate the proper consistency for each engobe. The consistency is tested by running a brush across the cardboard and noting how smoothly the engobe flows from the brush.

On one "bone-dry" red plate, draw the design free hand, with pencil, using the drawing on the paper for reference. Do not retrace the pencil lines. Draw them in with long single free strokes deftly and fairly rapidly. Do not dig the pencil point into the clay body.

Now with the brush, paint with the white engobe first. Paint over and along the pencil lines (which are to be painted white) quite rapidly. The brush stroke should be quite free and rapid. Seldom paint more slip over slip already painted on. Further, never paint one moist slip on another; painting slip on top of moist slip will leave the slip surface quite bumpy and ridged. As an exception some slips, such as green, are quite thin, and are painted over white slip after the white slip has dried. (The dealer will generally indicate which slips should be painted over others.)

The other coloured slips are painted over the lines and points indicated for them. Do not putter by adding a bit of slip here and there. The simpler and more free the design and brush stroke, the more characteristic and delightful will be the final result.

The plate is fired to bisque after the engobe has completely air dried. A low firing transparent glaze is applied over the bisque and the piece is again fired for final form. See the text on transparent glazes.

The brushes are cleaned by squeezing out the slip from the camel's hair over the pertinent bowl and then rinsing the brush with water. The engobe may be permitted to dry in the bowls. The clay of the dried engobe can be pulverized and used over again to make fresh engobe.

The engobes are generally lighter and pastel in colour, in slip form. The final colour after firing is generally much brighter and deeper. The use of a decorating wheel will be helpful in painting borders of plates.

Part II. Sgraffito method

Materials: Same as in part I this lesson, plus a 2-inch paint brush.

Fig 36

Procedure: With the 2-inch brush, paint the white slip across the "bone-dry" plate. All strokes should be in one direction. Avoid overlapping the strokes. Do not paint one stroke on top of another. Completely cover the plate with white slip. Allow the engobe to dry from 12 to 24 hours.
Apply the second coat of white slip at right angles or "crosswise" to the first coat (Fig. 36B) . Completely cover the plate with the second coat. Do not putter and touch up the plate here and there with more engobe. Permit this coat to dry from 12 to 24 hours. Do not handle the coated surface as the engobe may powder or crumble off.

Now trace the selected design lightly with a pencil on the plate (Fig. 36C) .

With the point of a scratching tool, scratch through the white engobe until the red body below is seen. Blow away the scratched off particles of engobe. The lines can be made thinner or thicker by the amount of engobe removed by the scratching tool. Do not dig into the red clay body to obtain thicker lines; just make the line wider by scratching off more engobe. For areas such as the border, the engobe is removed by using the flat edge of the scratching tool (Fig. 36D).

Handle the plate as little as possible after scratching in the design. The plate is now fired to bisque. After the bisque firing a clear transparent glaze is applied for glaze firing.

Note: The border is normally scratched out because it is most difficult to attempt to put the two coats of engobe properly on the plate inside a border line.

Part III. Polychrome method

Materials: Same as in part II, this lesson.

Procedure: The procedure for this method is exactly the same as for sgraffito, except that the scratched out areas are filled in by painting with engobes of different colour. It is desirable to draw the design in colour on paper in advance, as a reference when working in this method.
When engobes are dry, the plate is fired to bisque, a transparent glaze added, and the plate fired again.

Comments: The three methods of engobe decoration indicated above are not limited to flat plates or tiles, but can be used on any type of ceramic object.

Further, the body of the object may be coloured clay, and the engobe for slip painting, sgraffito, or polychrome decoration may be of different contrasting slips; not necessarily white.

Of course if the polychrome method is considered too arduous, different colours may be painted on the object directly without scratching out the first engobe coats. However, different slips have varying consistencies, and care should be taken to prevent thinner slips from infusing or running into the thicker moist slips; each colour should dry before applying another adjacent colour.


Ceramics:
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  • Glossary
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