PROBLEM: A BOWL FOR FLOWERS

This problem naturally divides itself into six important steps, as follows: The design or profile; building and shaping; decoration, if any; firing (bisque); glazing; and firing the glaze.

Variety in dimensions

The Design or Profile.—As in all problems of decoration the first step is found in design. For present purposes we may consider a bowl as having a diameter as great as or greater than the height. The bowl will be more interesting from the standpoint of variety if there is a difference between its height and its greatest diameter, and also between its diameters at the top and at the bottom. The accompanying drawing shows such differences.

Suggestive profiles

Another example of the value of variety is to be found in the curve of the profile. A line that is simple but constantly changing in its degree of curvature—as, for example, an elliptical curve—is more pleasing than an arc of a circle, which is sometimes called the curve of limitation. It should be noted that a curved form, in order to be forceful, should have some dominant curve in combination with others which are subordinate. The profiles illustrated in the following drawings have this dominant element and are in no case composed of arcs of circles. These varied, interesting, yet simple lines—live lines as they are sometimes called—consisting in each case of only two or three elements, are given here merely as suggestive material. A little experimenting will show unsuspected possibilities in strong, forceful curves, and the young student is advised to make many experiments in the effort to discover such possibilities. An example of profiles to be avoided is given in Problem II, on [page 309]. That these are vase forms and not bowl contours is immaterial. A is commonplace because the two parts of the curve are too much alike. B is unrestful in its three curves of nearly equal size. If the suggestive profiles illustrated in the foregoing drawing be turned upside down it will be noted that very few of them seem as pleasing as before. It will be found also that a different ratio of height to diameter will give very different effects with the same profile. A bowl having top and bottom alike may, so far as design is concerned, be classed with the pill box. We don't know which is the top until we have spilled the pills. If attractive pieces of pottery are found with the top and bottom of equal diameter and with curves in themselves objectionable, it will invariably be found that the attractiveness consists in some beauty of glaze, colour, or decoration which is prominent enough to conceal the defects of form.

Natural Forms.—It may be well to add a word here in regard to the imitation of natural forms in designing the general shape of any piece of pottery; and that word is a very brief one. Avoid them. Nature is a great teacher in all branches of art; but in pottery her suggestions are to be used as decorative elements rather than for fundamental shapes. A fish with a flower in its mouth does not seem appropriate; but a bowl for water-lilies, while it may not take the form of a fish, might reasonably have a fish as an element of its decoration.

Testing Profiles.—A good way to study the effect of the profile of both sides of the bowl is to fold the paper on which the profile is drawn vertically through the centre and transfer the line reversed by rubbing the back of the paper, thus giving the other half of the drawing in exact symmetry. When the general shape of the profile has been tested in this way one side should be redrawn carefully; then, with the paper folded along the centre line, so that the pencil line falls outside, the whole form may be cut out; and then it may be unfolded. The next step is to begin to build up the design in clay.

The Building.—Roll out a coil of clay a little thicker than the bottom of the bowl is to be; perhaps ³⁄₈ or ¹⁄₂ of an inch will serve, since the bottom is to be hollowed slightly by scraping. The roll should be uniform in diameter and rolled as little as possible, in order that it may not become too dry. Upon the piece of paper or the plaster bat start to coil the roll from the centre until the desired size is reached, then smear the rolls together, working toward the centre. Turn the coil over and work the other side together, truing up the circle and making the bottom of uniform thickness. Avoid the use of water in smoothing the coils together. It may seem to make the work easier, but it softens the clay and invites careless work.

Manipulating the coil

With another coil begin to build up the sides, making a complete circle, and, having pinched off the ends where they meet, join them carefully. Lay two or three coils in this fashion, pressing each coil firmly into place as it is laid, and smooth them together as in the base. The process is illustrated in the drawing. If the clay is very soft, the work may be set aside to harden a little, while a beginning is made upon other pieces. It is well to have two or three pieces in the process of construction at the same time.

Testing the Work.—A template or gauge will be needed to test the work as it progresses from the first rough stages to the finish. This is made of card-board by cutting out an exact copy of the profile, leaving at the bottom sufficient width to insure rigidity when the template is held upright on the table or bat.

A template

As the work goes on, if the design requires that the form should be "brought in" toward the top, the coil must be laid a little inside of the profile desired, as the smoothing tends to increase the diameter slightly. In all the building, allowance should be made for this enlargement. When the coil is high enough and of the shape desired, it should be allowed to stiffen until it is rigid enough to handle. With the various modelling tools the surface should then be scraped wherever it is necessary to remove the hardened clay in order to give a symmetrical shape to the desired profile.

Scraping a square form

A drawing is shown to illustrate the process of scraping. The surface should be left smooth and even; and this may be accomplished without water or sponge. The flat sides of the scraping tool may be used to polish the clay as soon as it becomes leather hard—i. e., hard and stiff, but before it begins to whiten and dry.

The lip or top of the bowl will require special attention. It will probably need to be thinned down and have all sharp edges removed. Then the bowl should be turned upside down and the bottom hollowed out to a depth of ¹⁄₁₆ to ¹⁄₈ of an inch, leaving a "foot" or rim around the outside of the circle to give it steadiness.

The Decoration.—After the bowl is complete as to its general form, the problem of its decoration, if there is to be any, must be solved. This may be studied during the intervals when it is necessary to set the bowl aside to harden. If the form and colour are good, the bowl may possess a charm that will not be improved by decoration. On the whole, less decoration, rather than more, should be the aim. The three vases illustrated at the top of a following page are examples of pottery without decoration. (See [page 308].)

Bowls

[Plate XII]

Generally speaking, bowls like the one we are building may be decorated by one of three methods: By sinking lines or channels in its surface by means of a sharpened, chisel-like stick (D, [page 285]); by modelling or carving the surface; or by painting the surface with coloured "slip" or with coloured glaze. It should be explained that "slip" is a mixture of clay and water of the consistency of cream; it may be coloured or uncoloured. A combination of two or more of these methods is, of course, possible. Examples of the first two methods are shown in the illustrations of bowls, vases, and tiles. A combination of the first and third methods was used in decorating the tiles of the middle row shown in [Plate XIV opposite page 316].

Spacing in decoration

Classes of Decoration.—The form of the decoration is simply a matter of space division, as illustrated by two examples shown below. It is evident, too, that decoration, so far as form is concerned, divides itself naturally into three general classes: (a) The horizontal band; (b) the vertical division; (c) a combination of these two. The last will prove to be the most common of the three. It should be noted that an all-over pattern, which has been left out of consideration as tending to monotony, would commonly be a combination of both horizontal and vertical methods of division. It should be noted also that the presence of other than vertical and horizontal lines in pottery decoration does not affect the main classification. Typical examples of these divisions are illustrated in both bowls and vases, as well as in the cuts A and B. It will be seen in each case that one scheme or the other predominates and that there are possibilities for great variation in treatment.

Analyzing the patterns shown in all these illustrations, we find that the band or horizontal scheme offers a succession of large and small spaces, giving variety and rhythm. In many of those patterns showing the combination type there is a concentration or "knotting" of the line at regular intervals, frequently at the intersection of both horizontal and vertical elements. This is well illustrated by the left-hand bowl of the middle row shown in this plate opposite [page 294]. When the method of painted decoration is employed the concentration point is composed of mass instead of line. All this serves to give emphasis and rhythm.

For subject matter in decoration natural forms may be used as shown in the vase at the left of the top row illustrated in [Plate XIII, opposite page 312]. Or an abstract arrangement of lines may be employed, as shown in its nearest neighbour, which may or may not have had its origin in a very much conventionalized natural motif. The essential thing to remember is that the divisions of spaces must be varied and rhythmic and the decoration suited to the method of application.

How the Design is Applied to the Clay.—After the design has been studied as much as possible on paper it should be planned out on the bowl with a soft pencil, allowing sufficient space for the incised line or channel to be made. The clay should be leather-hard—i. e., stiff but not dry. The spacing around the circumference should be made exact, deviating somewhat, if necessary, from the spacing of the paper drawing. A good way to manage this important step in the process is to measure the circumference at the point of greatest width with a narrow strip of paper and then to divide this circumference by folding the paper evenly into the number of units desired. By wrapping the paper around the bowl again the points of division may be transferred to the clay and then projected upward or downward vertically to the belt that it is desired to meet. It is necessary to make sure that the vertical lines are true "meridians" and do not swerve to the right or the left. In order to test the horizontal lines, measurements may be made from top or bottom. All of this work is best done free-hand; for, aside from the value of the eye training derived, hand-built pottery is seldom exact enough to permit of a more mechanical method of planning its decoration.

The drawing on the clay having been completed, the next point is to choose the tool best fitted for the work and carefully make the cuts, deepening them from time to time as the work progresses. If the design is to be worked out in line, a chisel, like that illustrated in D ([page 285]), may be whittled from a pine stick. It is held nearly upright and used as a scraper to cut out at first a shallow channel. Reserve should be exercised in cutting, because, generally speaking, there is danger of making the design too insistent. Some of the best designs are very subtle and quiet. Care should be taken, however, to allow for a slight filling in of the hollow by the glaze when it is applied.

Modelling a Decoration.—If the decoration is to be modelled it would seem wise to do it, in whole or in part, as the work is built up; but in this case great care will be needed to keep a firm hold on the relief and unity of the decoration. It will be easy to over-model the work.

How Under-glaze is Applied.—For decoration with under glaze the colours given under the head of glazing ([page 304]) are mixed in different proportions with dry powdered clay and water to form a colour paste. This is painted on the "green" or moist clay, forming a smooth and even surface. Experience will teach the proportions of colour to be mixed with the clay. These proportions vary greatly with different colours. A very strong colour like cobalt will give a deep blue if mixed in the ratio of one part by weight of cobalt to ten parts of clay. Colours like the oxides of iron and copper are of medium strength, and antimony is quite weak.

Before the work is left to dry it would be well to make sure that all corners and rough edges are smoothed off as they will show light and rough through the glaze. The use of sand-paper, however, is not advised, though it may occasionally be used in the emergency of an accidental roughness remaining after the piece is dry. The aim should be to have all clay work show something of the plastic nature of the material out of which it is made.

Firing.—Pottery must be "bone" dry before it is fired. A very satisfactory portable kiln for firing may be purchased for from $34 to $175, according to the size. The smallest size, which is illustrated in the next drawing, will be ample for the needs of one or two persons. If, however, the amateur does not care to go to the expense of purchasing a kiln, it is generally possible to find a pottery factory in the vicinity that will undertake the firing and perhaps the glazing.

A portable kiln

Temperature Required.—Pottery is fired at a temperature varying, according to the clay and the glaze used, from approximately 1800 to 2000 degrees Fahrenheit. Modelling clay fires at 1958 degrees Fahrenheit, or what is called "cone 04." This term comes from the fact that the heat is gauged by pyrometric cones, which can be seen through a spy hole attached to the kiln. These cones are graded compositions of various materials and possess different degrees of resistance to heat. They are usually set up in clay in groups of three or more. When one of them melts it bends over, as illustrated in the accompanying drawing, which shows cone 05—the most fusible one—completely "down," and 04 at a point indicating that it is time to shut off the heat from the kiln. This must be done gradually and the kiln must be allowed to cool completely before it is opened. This is especially necessary when firing the glazes described in the following section, which require the same temperature as modelling clay. Further details about firing and caring for the kiln may, of course, be learned from descriptions accompanying the apparatus. Pottery comes out of the first firing in the kiln a dull porous ware and in colour either cream, buff, or red, according to the amount of iron in the clay. In this state it is called "bisque" or "biscuit."

Pyrometric cones

Glazing.—It is necessary to bring the pottery up to the condition of bisque before it can be glazed; or, to speak more accurately, before it can be over-glazed; for it has already been shown how the so-called under-glaze is put on before the first firing. The subject is somewhat technical, and it will not be possible in a single chapter to take up the details extensively. Briefly speaking, the glazes most used for this class of work are the lead glazes—combinations of "white lead" or carbonate of lead as a flux with kaolin, flint, whiting, feldspar, and other ingredients. These are supplied in powdered form and are ground together in water by means of a mill or a large mortar and pestle; a mortar 8 inches in diameter will serve.

Grinding the Glaze.—The grinding should continue about an hour. It should be said, however, that there is such a thing as grinding too fine. After the glaze has been properly ground a small quantity of gum tragacanth, dissolved in water, is to be added as a binder to prevent flaking and rubbing off in handling. It is also a good plan, though not always necessary, to strain the glaze, as soon as it is ground, through fine muslin. The tools and materials needed for this work may be itemized as follows: Lead carbonate, whiting, Canadian feldspar, Florida kaolin, French flint, white oxide of zinc, and various other oxides and colours noted in the text; earthenware bowls, 10 or 12 inches in diameter, for holding the glaze; large spoons, preferably aluminum; agate mortar and pestle, 8 inches in diameter.

Example of Matt Glaze and Bright Glaze Mixes.—Two mixes are given below calculated to fuse at cone 04. One has a "matt" or dull velvety surface, and the other has a "bright" or shiny surface. The matt will be found more desirable for general work because it harmonizes better with flowers and foliage. The figures given below refer to units of weight. Metric weights (grams) are most convenient to use, but any units will serve so long as the same one is used throughout. The matt glaze should be of the consistency of thick cream, the bright glaze somewhat thinner.

MATT BASE		BRIGHT BASE
Lead carbonate	154	Lead carbonate	142
Whiting	25	Whiting	20
Canadian feldspar	83	Canadian feldspar	84
Florida kaolin	51	Florida kaolin	8
		White oxide of zinc	8
		French flint	44

The bases itemized above are colourless and there must be added to them from 3 to 6 per cent. of colouring material that will stand heat. A list of materials with their colours when fired is given on [page 304], together with a few typical combinations of colours in quantity suitable to be added to the glaze bases given above. The following lists are by no means complete, and it is expected that the young decorator will make use of these colour mixtures simply as an introduction to quite extensive experimenting:

COLOUR MATERIALS
Black oxide of cobalt	Blue
Black oxide of copper	Blue green
Green oxide of chromium	Yellow green
White oxide of antimony	Lemon yellow
Red oxide of iron	Yellowish brown
Green oxide of nickel	Dirty gray (for neutralizing)
White oxide of tin	Makes glaze opaque
Black oxide of manganese	Purplish brown
Yellow ochre	Yellow
Burnt umber	Brown

COLOUR COMBINATIONS
Olive green		Blue-green
Iron oxide	5	Cobalt oxide	1
Cobalt oxide	.5	Copper oxide	7
		Yellow ochre	4
Dark brown		Dark gray-blue
Iron oxide	3	Nickel oxide	5
Nickel oxide	2	Yellow ochre	3
Manganese oxide	5	Cobalt oxide	2
		Copper oxide	1
Light gray-blue
Tin oxide	5
Cobalt oxide	.5
Copper oxide	1.7

Applying the Glaze.—Before applying the glaze to the piece of pottery or bisque, the latter should be soaked in clear water for about five minutes or until the air is expelled from the pores. When this has been accomplished it should be removed from the water and all moisture should be wiped from its surface. The piece is then ready to be dipped into the glaze, or to have the glaze poured over it, if the size and shape of the piece make it more convenient to apply the glaze in this way. It is usually best to glaze the inside first, shaking out all the superfluous glaze before applying the glaze to the outside. During this process the piece must be held firmly but by as few points of contact as possible. These points of contact will generally need to be touched up before it is ready for firing.

It is sometimes necessary to glaze large pieces with a brush, putting on several coats in order to cover the surface with an even thickness. The matt glaze requires a greater thickness than the bright glaze in order to develop its characteristic velvety texture. The greater thickness may be easily secured, because it flows more slowly than the thinner bright glaze and is less likely to drip from the sides of the piece to which it is being applied; but, on the other hand, it is at a disadvantage in that it does not, in flowing slowly, correct inequalities of thickness so readily as the more mobile bright glaze does. A certain thickness, however, is essential; and if, after firing, it is found that the glaze was put on too thin, a second coat may be applied and the article again fired.

Firing the Glaze.—Before the glazed piece is fired the glaze should be dried and what runs down and collects about the bottom or foot should be scraped off. It should then be set in the kiln on a kind of pointed tripod of hard burned clay, called the "stilt," which prevents the glaze from sticking to the floor or shelves of the kiln. All glazed ware should be placed in the kiln with at least ¹⁄₂ an inch of space between the pieces to prevent them from sticking together during the fusing state of the glaze, when it is apt to bubble or "boil."

The firing of glaze is a process very similar to that employed in the production of bisque, already described. Greater care, however, must be taken in controlling the increase in temperature so that it shall be even and steady—free from all sudden flashes of heat. The cooling also should be very gradual and, as in bisque firing, the kiln should be allowed to get cool before it is opened. With this second firing the pottery is finished unless it should happen that a second coat of glaze is found to be necessary. If only a few spots need attention, this second coat is best applied with a brush.