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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.)
[Illustration: 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.
[Illustration: 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.
[Illustration: 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."
[Illustration: 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
Lead carbonate 154
Whiting 25
Canadian feldspar 83
Florida kaolin 51
BRIGHT BASE
Lead carbonate 142
Whiting 20
Canadian feldspar 84
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: