the potters wheeel for model making
Part I. The potter's wheel
The Wheel: Archaeologists, digging into
the ancient ruins of Ur near the mouth of the Euphrates River, have uncovered
pottery, in layers of the earth just above the level of the Great Flood
of Noah's time, which were made on a potter's wheel. At Tell Billa, near
the headwaters of the Tigris River, wheel-turned pots, made about 3200
B. C., were also unearthed.
It is believed that the first potter's wheel
was a crude balanced stone, which was rotated by hand. With human ingenuity,
however, various types of potter's wheels were evolved in different lands,
each varying slightly but using simple mechanical principles. The use
of an assistant to turn the wheel by hand; the use of a foot pedal in
a crank-like action; the turning of the wheel by rope or belt drive were
among the kinds developed. However, with the machine age, considerable
improvement in wheels is noted.
Of the types in common use today, the kick wheel is probably the
oldest and simplest. The kick wheel comprises a "throwing"
head (a horizontal circular disk) mounted on a vertical shaft which
is supported by a bearing. At the base of the shaft a heavy balanced
fly wheel is attached. The seated operator kicks the fly wheel with
the foot, while manipulating the clay on the throwing head with
his hands (Fig. 33).
An improvement on the kick wheel is the type which is operated by
a foot treadle which turns the fly wheel.
The latest improved types are electrically
operated, electrically adjustable in rotating speed by foot control,
have interchangeable throwing heads, and come with attachments for
catching clay drippings, for providing water, hand rests, and other
Throwing heads are made which are
removable-so that if several students are using the same wheel,
each can put on his own throwing head, or remove it to store his
work until a later time when he has an opportunity to use the wheel
again. Professional throwers
prefer a smooth wood or brass throwing head because the clay to
be worked is more easily centred thereon. However, for ease to the
beginner, a plaster bat type of throwing head is normally used.
Throwing: The procedure
of forming a clay object by hand on a potter's wheel is known by custom
as "throwing." It is practically impossible to learn how to
"throw" on a potter's wheel from a site. To learn properly it
is necessary to study under the supervision of a skilled operator; and
proficiency is gained only after considerable practice.
Here we shall describe the general principles and procedure so that you
may have an acquaintance with the subject. A plaster bat is cast inside
a circular metal hoop which fits into an indentation in the throwing head.
A ball of clay is slapped on as near to the centre of the plaster bat
on the throwing head as can be estimated (Fig. 34A). This clay is much
more moist than normal plastic clay and is frequently sprinkled with water
by hand during operation to keep it in the soft moist condition.
Remember that all during the following discussion
the wheel is spinning or rotating. The
head is rotated at a fairly rapid speed. At the outset, one hand is pressed
against the spinning ball of clay forcing it to centre itself. Both hands
are then pressed inward against the sides of the clay mass to cause the
clay to rise. In throwing, clay is never pulled upward. It is forced upward
by squeezing inward with the hands lower down on the clay mass.
As the second step, the
clay is wedged on the wheel. This is accomplished by squeezing inward
with both hands to force the mass up (Fig. 34B), and then pressing
on top of the mass to flatten it down again (Fig. 34C). The clay
is forced up and down in this manner several times until the clay
body feels smooth and uniform throughout.
After the clay is properly wedged,
the next step is to form a hollow object. The thumb of one hand
is pressed down on top in the centre of the mass, while on the outside
surface the clay is pressed inward with the fingers of the other
hand. As the hollow enlarges, the fingers of the inside hand are
inserted (Fig. 34D).
Pressing down and outward with the
thumb and fingers of the inside hand while opposing the pressure
with the fingers of the outside hand is the basis of forming a hollow
in a thrown object. If the inside finger pressure is greater than
the outside finger pressure, the wall of the object will move outward
at the point of pressure. If the inside finger pressure is less,
the wall of the object will move inward at the point of pressure.
If the pressure of both hands or fingers is equal and opposite each
other, the wall will rise straight up in cylindrical fashion.
The student next throws an erect cylinder,
making the walls as thin as possible without collapsing the object
(Fig. 34E). This practice gives him the feel of wall thicknesses
and the possibilities of the clay.
The student then practices to form a simple,
wide, shallow, flat-bottomed, straight-sided bowl in order to learn how
to form clay out at a distance from the centre of the throwing head (Fig.
After this, the student
attempts an upward outward curving bowl and thus learns the relative
inside and outside finger pressures required, and the positions
of the fingers of both hands with respect to each other. In curving
the wall upward and outward, the fingers of the outside hand press
in slightly below the fingers of the inside hand which are pressing
outward (Fig. 35A).
In like manner, to curve the wall
inward, the fingers of the outside hand press in slightly above
those of the inside hand (Fig. 35B).
After the outcurving and incurving
bowl shapes are mastered, the student practices in making globe
shapes, first curving the lower part outward, then bringing the
wall back in the upper part of the object (Fig. 35C). A good proportion
of the clay mass is forced toward the top at first as the shape
curves outward, so as to provide clay body for the top portion as
it is thinned and forced upward and inward (Figs. 35A and B).
In making a vase, the lower walls
are thinned to their final thickness before the clay on the top
is worked inward to form the neck. It follows that considerable
clay will have to be forced to the top at the beginning so that
there will be sufficient clay mass from which to form the tall narrow
neck. It is obvious that once the narrow neck is started, it is
impossible to get the hand inside to thin the walls of the lower
bulge further; these will have been formed to final thickness prior
to commencing on the neck.
Once the feel of the clay, the sense of
central balance of the clay mass, the relative pressures and positions
of the fingers of each hand, and the knowledge of the amount of clay to
force up to complete the top becomes instinctive through practice, the
student is capable of throwing any type of shape on the wheel.
But the real craftsmanship is evidenced
when the operator is given a drawing of an object with stated dimensions
and can fabricate the object exactly. He may make a template (a metal
or plastic profile of the shape) or use measuring callipers to check his
work as he progresses; but the final result must be accurate and correct.
Obviously, this capability is developed with a great deal of practice,
and the operator must have an innate feel for throwing.
Turning: While throwing
an object, the hands are always kept wet, and the clay is sprinkled frequently.
The clay is therefore quite soft, and shows every mark or imperfection,
intentional or unintentional. It is necessary, therefore, to "finish"
the surface of the object before it can be considered completed. The process
of finishing a "thrown" object is called "turning."
After the object is thrown on the wheel
to satisfaction, it is permitted to dry to leather hardness. It is only
when the object is leather hard that it is "turned."
In turning, a steel scraper is used to cut
the surface of the object. These scrapers can be purchased already shaped,
although many craftsmen prefer to buy the steel blanks, and shape and
sharpen scrapers to suit their own preferences. Broad scrapers are used
for slow curves, while narrow pointed scrapers are used to cut sharp corners.
The leather-hard object may be retained
on its original plaster bat throwing head and reinforced with plastic
clay lumps at the base. However, some prefer to remove the object from
the throwing head with a long thin sharp knife, or wire, centre, and remount
it on another somewhat moist plaster bat head. After remounting, the object
is reinforced with plastic clay to hold it in place.
In turning, the scraper is held so that
the cutting edge faces against the direction of rotation, and the plane
of the metal cutting surface passes through the axis of rotation of the
object (Fig. 35D). The scraper is held against a tool rest to insure accuracy
and prevent vibration. The scraper actually cuts the surface of the clay
to a fine smooth finish. It takes considerable practice to use the scraper
properly. After the surface is polished, the piece is centred on the throwing
head upside down, and a footing is cut into the base (Fig. 35E).
The type and quality of the footing of a
fine vase are a measure of the care and craftsmanship expended in its
construction. Several types of footing are illustrated (Fig. 35F). The
turning gives the object the fine finish and ultimate accuracy which is
the pride of the best craftsmen. However, considerable experience is required
before "turning," as well as "throwing," is mastered.
Part II. Aspects of plastic model making
The Model: Second to the
pleasure of creating a brand new ceramic design is the satisfaction of
making numerous reproductions of this creation-either for your own use,
to present as specially personalized gifts to friends, or for sale!
If the design is complicated, the making
of perhaps a dozen replicas by hand methods may prove quite tedious and
arduous. Obviously, the use of the original as a model from which a mould
can be made and replicas cast is preferable by far. However, there are
several principles and precautions that should be observed in making the
original model if you intend to make reproductions from it.
Modelling Media: As indicated,
models may be made from metal, wood, glass, plaster of Paris, plasteline,
modelling clay, plastic clay, bisque, or glazed ware. However, in creating
an original model, it is obvious that the plastic media-plasteline, modelling
clay, or plastic (ceramic) clay-are the easiest with which to work, are
the most responsive, and can be most easily corrected or modified if you
wish to change any details. But, if you use plasteline or modelling clay,
the model will always remain soft, and may be disfigured during the making
of the mould.
The use of plastic ( ceramic) clay is recommended
above all others in making the original model. In addition to requiring
a minimum of effort in making, a plastic clay model can be fired to bisque,
coloured to final design, and smooth-glazed so that you can actually see
what the final decorated result will be before you begin mould making
However, the use of leather-hard or bone
dry (green) plastic models directly in mould making is undesirable, as
these may collapse during mould making. Models fired to bisque are better
because they are more rigid. However, shellacking or other means of sealing
the pores of the bisque is necessary before mould making. The most desirable
method is to design the original in plastic clay, fire to bisque, and
then fire on smooth glaze. The use of smooth-glazed models simplifies
mould making and avoids complications which arise in using other types
Principles in ceramic model making:
Follow the principles listed below when designing original objects if
you intend to cast replicas afterward.
- Clay objects when fired to bisque shrink
about one-eighth in all their dimensions. In building the original model,
make it larger by at least one-eighth than the final desired size.
- Always use well-wedged clay in model
making. The model is to be bisque fired and then glaze-fired. If there
are air pockets or the clay is not of uniform consistency the model,
like any other ceramic object, may crack or warp on firing.
- At no place in the model should the walls
be more than 1 inch thick. Upon firing, the chemical water vapour released
in the clay may set up internal stresses within too thick walls of the
clay and cause them to crack. After establishing the composition, while
the clay is still plastic, and before finally finishing the surface
of the model, scoop out the clay from the inside of the model with a
spoon or modelling tool. Scoop so as to reduce the wall thickness to
less than 1 inch. The clay is generally scooped out from the bottom
of the model.
If it will spoil the model, or if the excess clay cannot be reached
through the bottom, another method of scooping may be used. With a thin
sharp knife cut the model in half in the middle or at the thickest portion,
horizontally. Scoop out the excess clay in the upper and lower halves
of the model and reduce the wall thickness to less than 1 inch. The
pieces are then carefully slip pasted and wedged together. Complete
the surface details.
Never cut the halves vertically or at a slant. Upon firing, the horizontal
pieces, because of the weight of the upper half, will fuse together
nicely. If cut vertically or at a slant, the parts may separate on firing.
If the object was cut across for scooping out, always fire the object
very slowly to bisque.
- Always design a fairly large base for
your model. This is done for support and prevents easy tipping over
and breakage of the model and its reproductions. Also, when the object
is being fired to bisque and the heat approaches maturity, the chemicals
and flux in the clay begin to fuse and melt, the clay may become somewhat
soft, and the object may collapse if a very small base is employed.
If you examine any ceramic object you will note that in most cases the
base is quite substantial-generally larger than the top. Figurines are
usually supported by tree trunks, columns, or other decorative support.
Incorporate supporting columns in the dynamic design of the figure.
Do not attempt to design a ballerina or other dancing object supported
by a toe or one foot, without incorporating a supporting block, column,
or other type support. The toe or foot will collapse on firing.
In the finer ceramic statuettes, the dancing or delicate figures are
designed and fired separately with special firing techniques. As an
example, in firing a long, thin legged colt, the belly of the colt is
supported by a "bisque saddle," which holds up the body and
keeps the weight off the legs during firing.
- Design your model so that it requires
a minimum number of mould pieces. This means that as much undercutting
as possible should be avoided. To best understand what is meant, you
should make at least one three-piece mould from a selected model. See
lesson IX. It will become apparent that if the model is kept simple,
and unnecessary undercutting is avoided, the number of mould pieces
is reduced, and the difficulty of reproducing replicas is considerably
In incising or embossing designs on the surface of the plastic clay
object, make sure that the cuts or rises are perpendicular to the surface,
or slant to avoid undercutting. Technically, in embossing, the sides
of the embossed clay should make a right angle or obtuse angle (in the
clay) with the plane of the clay surface of the model, at all points.
In incising, the sides of the cut should make a right angle or acute
angle (in the clay) with the plane of the clay surface of the model,
at all points. Plaster of Paris makes an exact reproduction of the model,
does not shrink, and will run into an undercut in incising or embossing,
and will make removal most difficult.
Where an arm or special part of the design extends out at some distance
from the main part of the model, this part can be cut off, fired, glazed,
a mould made therefrom, and the part cast separately. While the cast
part is leather hard, it can be removed from its mould, and slip pasted
to the casting of the main part. This is often done to avoid too numerous
and complicated mould pieces.
Note: When making a model for an important composition, the design should
not be sacrificed or abandoned because of the mould making aspect. The
design should be made in a solid unit, but if possible modified to avoid
or reduce undercutting and unusual protruding parts, to minimize the
number of mould pieces.
- In finishing the plastic model, avoid
sharp edges. Sharp edges will not always mould or cast well. Furthermore,
glazes, on firing, tend to run away from sharp edges. Gently round the
edges of the model while in "bone-dry" or bisque condition.
- Hint 1. Original, hollow,
round models, such as bowls or vases, are best thrown on a potter's
wheel. The model can be built by hand methods but it is most tedious
and difficult to get an absolutely symmetrical design. While it is true
that a student cannot learn throwing on a potter's wheel from a site,
the fact remains that the potter's wheel is the best means for making
symmetrical, cylindrical, or circular models.
- Hint 2. In modelling
a head or a straight up-and-down type of model, it is often convenient
to use a wooden broom handle as an "armature" or support,
around which to build the plastic clay. Upon removal of the broom handle,
the cavity remaining serves to keep the walls of the model thin, and
avoids to a great extent the necessity of scooping out the excess clay
in the centre.
- Hint 3. Always conceive
your design in terms of the material you are using. A design that is
suitable for bronze casting may not be suitable for a ceramic object.
A fine delicate design suitable for metal casting may collapse if cast
in clay, during drying, or during firing. Metal walls can be made much
thinner than is possible with clay.
- Hint 4. Metal, or glass
hardens after casting. Clay is fragile while leather hard or "bone-dry";
it softens on maturing in the bisque firing. It only becomes hard upon
cooling after firing. This must be constantly borne in mind.
- Hint 5. In designing
models for reproduction, commence with very simple items, requiring
only one- or two-piece moulds. After practice in designing and mould
making, you will have learned the capabilities of the plastic clay medium
and the precautions to observe in making the more complicated designs.
The more complex models should then be attempted.