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Basic Throwing
- by Bill Geisinger
Beginning potters who doubt their ability to throw, or believe that
throwing ability is an innate talent rather than a learned skill,
should be pleased to know that history shows without question that
nearly anyone can become proficient at throwing on the potter's wheel.
Because of their inexperience, beginning potters may assume that most
of the problems they encounter while throwing are the result of a lack
of skill. To improve their skills, beginners should be concerned with
the advantages and disadvantages of the various tools, equipment, and
materials used for throwing. At times a simple adjustment in tools,
equipment, or materials will solve a problem.
Tools of the Trade
There are many tools available to aid throwing techniques. A basic
group of tools for beginning potters might include the following:
* Elephant ear sponges for adding or removing water
* Wood modeling
tools or pencils for incising and for undercutting the base of
a piece of ware prior to removing it from a wheel head
* Wood ribs with one
curved and one straight side to use in place of the fingers for
pulling, flattening, or straightening a surface
* Needle tools with
the wood end sharpened for cutting and incising
* Cutting wire or
string for removing a piece of ware from a wheel head
There are a number of commercially manufactured tools which you can
add to this list as needed, and you can improvise with common items
such as pencils, dish sponges, etc. Personal experimentation will help
you decide which tools and materials work best for your own needs.
Clay Bodies
The clay body selected for throwing is as important as the type of
wheel and wheel head used. There are three general groups of clay
bodies - red or white earthenware, stoneware, and porcelain. Stoneware
usually has the best working properties. Because it is not always as
workable as an earthenware body, and porcelain is generally considered
a poor clay to use when learning to throw.
Wedging the Clay
After selecting a clay, you must wedge (knead) it to remove air
bubbles and insure uniform consistency. A clay body that has been
mixed properly and extruded from a de-airing pug mill is homogeneous,
and because a vacuum removes most of the air, it does not usually need
as much wedging for its first use.
There are two common kinds of wedging, the cut wedging method
associated with potters in the Western world and the spiral wedging
method associated with potters in the Eastern world. The spiral method
is more efficient, particularly when wedging a large chunk of clay,
but the spiral method does take longer to learn. Cut wedging is only
successful when the clay is very soft, so it is only recommended if
you are mixing a very wet and a very dry chunk of clay for later use.
Spiral Wedging
The spiral wedging method has three main steps:
1. Push a cone of clay away from your body on a horizontal surface
with the heels of your hands (the left hand does most of the work).
2. A thick slab of clay is created by this pressure. Partially roll
this slab of clay back onto the cone with a twisting
motion of your hands.
3. Repeat the process.
With each pushing motion, the tip and lower surface of the cone are
partially squeezed off, leaving the form with less mass. When the
rolling action takes place, new mass is added to the form.
Cut Wedging
Cut wedging has two steps:
1. Cut a chunk of clay in half with a wire that is attached
diagonally between a horizontal and a vertical surface.
2. Slap half of the clay, cut face down on the horizontal surface.
Throw the other half of clay, cut face up on top of the first half.
Repeat this step until the lumps, soft spots, and air pockets are
removed from the clay.
Preparing the Wheel Head
Prepare the wheel head for throwing by applying a thin film of water
or slip with your hand (wetting the wheel head is particularly useful
when the clay is rather hard; when soft clay is used, this step is not
necessary). Next, place a lump of clay on the wheel head and twist it
back and forth until it is firmly secured. If there is too much water
on the wheel head, it will take a long time to seat the clay.
Beginners should use soft clay, because it is easier to work with
during most of the throwing operations. If the clay is too stiff to
work with, you can dip it in a bucket of water and wrap it in plastic
or wet cloth. You can also cut stiff clay into chunks and sprinkle it
with water to soften it. If the clay is wet enough, it can be
re-wedged. If not, you can wet it again, wrap it in plastic, and
stored it until it is softened.
To attach clay to the wheel head without applying a film of water,
press or throw a lump of clay onto the surface as close to center as
possible. As the wheel rotates slowly, firmly slap the lump into
relative center. No lubrication (water) is applied to the clay during
this step. Peaks and valleys on the surface of the lump should be
smoothed with firm, rhythmic slaps, and the overall contour of the
clay should be forced into a symmetrical shape. If this is difficult,
the clay is probably too hard. Only when the clay is firmly secured to
the wheel head and relatively in center are you ready to begin the
centering process.
Centering the Clay
The theory of centering is simple. A lump of malleable material (clay)
is placed on a revolving surface (wheel head), forced into a
symmetrical form by contact with a fixed object (the hands), and
lubricated to reduce friction. Most beginners have difficulty with
centering because they release their hands from the fixed position
suddenly, thus affecting only a portion of the revolving surface of
the clay. You have to concentrate on releasing the hand pressure
slowly, so that the clay is not thrown off center.
The leverage which results from your hand-arm-body position is
particularly important for centering and is far superior to brute
strength. The heel of your hand, because it is the least flexible
surface of the hand and the most resistant to the pressure of the
moving clay, is used to apply pressure during centering. Your arms are
tucked against your body for support. If you allow your elbows to
move freely away from your body, you will loose leverage. By
positioning your upper torso over the wheel head, you can use your
body as a point of leverage and a bracing surface. There are, of
course, many potters who are able to throw successfully in other
positions; however, other positions require more physical strength. As
a beginner you will achieve better control in the braced position.
The Centering Process
1. Attach a grapefruit-size mass of clay to the wheel head, and slap
it into relative center.
2. Lubricate the clay with water, and increase the wheel speed to
about 160 rpm (or as fast as the wheel will comfortably rotate).
Periodical lubrication allows your hands to slide smoothly over the
surface of the hump. Keep the clay evenly lubricated, but work toward
the eventual reduction of the amount of water used. An elephant ear
sponge is a good choice for transferring water to the revolving clay.
3. Begin by repeatedly exerting upward and inward pressure from the
bottom to the top of the clay. Centering pressure involves more than
simply pushing the clay. Opposing muscles of the arms and hands are
tensed against each other to stabilize the hand contact surface - and
are gradually relaxed after the hump is centered. The best leverage is
attained when your upper arms or elbows are pressed against your body
to eliminate unnecessary movement. Avoid learning to center
with one or both of your arms resting on the splash pan, boards, or
other structures attached to the wheel. Although this practice may
seem to increase control at first, it will be limiting later when you
try to center larger amounts of clay.
The base of the hump is more difficult to control because the wheel
head interferes with your hand pressure. Also, if a heavily grogged
clay is being used, the abrasive nature of the clay may make working
with this portion of the hump uncomfortable. To minimize the
discomfort, use your fingers to apply pressure to the base of the
hump, or hold a sponge between your fingers and thumb to align this
surface. The sponge will protect your fingers from the abrasive
particles on the wheel head while distributing water evenly on
the surface of the clay ball.
There are three common problems encountered when centering:
1. If the clay is being forced to move too fast and cones up quickly,
it may break off in your hands. Insufficient or uneven lubrication can
also cause breakage. There are limits to what clay can do, and
beginners must learn to restrict pressure, speed, and friction to meet
the demands of the clay. (Broken off clay should not be replaced on
the hump. Instead, it should be re-wedged later with other clay
scraps.)
2. A hollow can form in the center of the hump as it is being raised.
To correct this, press down on the rim of the hollow while maintaining
the diameter of the hump; this pressure will force clay up from the
bottom of the hollow. Then, collar the form (collaring is discussed on
page 10) by applying pressure on the outside of the hump. Repeat both
processes until the hump forms a point. Avoid trapping soft clay,
slip, or air in the hollow as it is being closed.
3. The clay can move off center. If, during centering, the clay is
forced two inches or more off the midpoint of the wheel head, stop the
wheel and return the hump to relative center. Begin the centering
process again.
Successful centering is the result of practice and concentration, but
beginners have a tendency to underrate the importance of this process
because it does not produce a finished product. It is tempting to
rush through this preparation and "make something." However, centering
is extremely important. Failure to center the clay will impair all
phases of throwing that follow. Specifically, it will cause the thrown
form to collapse from the centrifugal force of rotation, or it will
produce an uneven wall thickness and height, which are difficult to
manage.
Alternative Centering Methods
You can use different methods of centering when throwing large amounts
of clay and/or wide-based forms. Because most hands will not cover the
entire surface of large humps, more strength or leverage is needed to
manage these forms. Consequently, the clay is manipulated from the
bottom to the top of the hump - pressure is applied and your hands
move slowly upward as the clay below is centered. The release of
pressure is gradual, and the process is repeated until the entire hump
is in center.
Two common centering methods call for opposing one hand's pressure
against the other at three and nine o'clock or at seven and one
o'clock, with the clay between the hands (hand positions are often
discussed as if the wheel head were a clock face). When using the
former method, your upper arms may be pressed against your torso; when
using the later method, your left elbow may be tucked against your
abdomen and your upper right arm pressed against your torso. Pull the
hump toward you with your right hand and force it away with your left.
This method offers much
more leverage because your back muscles and arms work together to
apply force. Once the sides of the large hump are in center, you can
center the top with downward pressure from one or both hands.
It is a good idea to master the centering process with small amounts
of clay before moving on to large amounts. There are many
possibilities for centering, and when choosing a centering method you
should consider leverage, adaptability for all quantities of clay,
comfort, and personal preference. It is encouraging to find a method
that works well and feels relatively comfortable when you are learning
to center on the potter's wheel.
Opening the Clay (Forming a Hollow)
Most conventional throwing involves the production of hollow forms,
and the rotating, centered clay must be "opened" by one or more
methods. The mechanics of opening are relatively simple - a centered
hole is forced into the hump to a suitable depth, leaving enough clay
beneath the opening for the base of the pot. The hollow thus forms the
beginning of the interior shape and wall thickness.
There are two steps to forming a hollow:
1. Press one or both thumbs, or a combination of fingers, into the
center of the hump. To avoid the formation of a peak at the bottom of
the hollow, apply pressure directly to the middle of the rotating
hump.
2. After reaching the desired depth, expand the hollow to form a flat
or slightly curved bottom. The bottom of the hollow is usually opened
slightly larger than at the neck, leaving a ridge inside which helps
the upward movement of the clay when the first pull is made.
Hints for Successful Openings
* Opening is performed at the same wheel speed used for centering,
and it also involves the tensing of opposing sets of muscles when
pressure is applied. The pressure used to open the clay should be sure
and even, and the downward movement should be direct, smooth, and
relatively fast. With the exception of the dimpling action, opening
is usually accomplished with one continuous motion; then pressure is
relaxed and the hand removed. Opening is a natural motion, because the
centrifugal force of the rotating clay helps guide you in achieving a
completely centered hollowing of the form. Quick or jerky movement,
particularly at the release of pressure, often results in an
asymmetrical and thus undesirable opening.
* If the clay is poorly wedged, you may find it difficult to make
an opening in the center. If you have this problem, the clay should be
re-wedged before further use.
* When you use your thumbs to open the hump, the depth of the
opening is limited to the length of your extended thumb. So this
method will only produce small or shallow forms, or it can be used for
opening the centered clay before further opening with your fingers.
Opening with the fingers is perhaps the most common method
because it is unrestricted - all sizes of forms can be produced and
only one method need be learned. With this technique, your fingers are
generally tensed together, and the fingertips are sometimes grouped in
an even line. Some potters brace or support one hand with the other
(right-handed potters may find it easier to open with the left hand
and brace with the right). The thumb is sometimes used to brace the
opening action of the fingers. If so, your thumb and fingertips are
grouped together as if trying to pick up a few grains of sand.
* Point the hand that exerts most of the opening pressure in the
same direction as the rotating clay. This helps prevent snags or digs
in the hump, which throw the form off center.
* Lubricate evenly. Some potters prefer to hold a sponge in the
opening hand to control lubrication and reduce friction.
* Form a small, shallow depression (sometimes referred to as a
dimple) at the top of the hump. This depression serves both as a
guide for further opening and as a container for water to lubricate
the opening action. This step is usually eliminated as potters becomes
more proficient, but it can be useful for beginners, particularly to
insure adequate lubrication.
* To form a stronger wall, use a thin clay slip to lubricate the
clay in place of clear water. Slip contains less water, and the less
water absorbed by the hump, the stronger the walls. This is
particularly advantageous to beginners, because they tend to overwork
the clay.
As you become more experienced, you will find the centering and
opening action flowing together, so that they are not separate steps
in the throwing process but rather are continuous patterns of
movement. Some experienced potters use withdrawal from opening as the
first pull of the clay wall. In this case, the thumbs or fingers move
outward from center when they reach the desired depth, and the clay is
squeezed as the hand is withdrawn.
Pulling the Clay
You are ready to pull the wall if the outside of the hump is centered
and the clay is opened in center. As your skill increases, it will
become apparent that pulling can also have a centering function - many
professionals use this technique. But as beginners, it will be
important to pull from a well centered and opened form. If the opened
hump is off center, the probable causes are either insufficient hand
tension, allowing the rotating cylinder superior force, or releasing
pressure too quickly.
Pulling has three main purposes: thinning the wall, extending the
form, and directing the shape.
Note: If further spreading of the bottom is needed, the indentation
is made prior to pulling. The lowest portion of the wall is squeezed
between a surface on the inside and another on the outside of the
wall. This helps trim away excess clay which spreads out at the base
of the wall by a method similar to the undercut described on Page 10.
Besides defining the base of the walls visually it helps the fingers
in raising the clay up from the bottom of the pot.
Thinning the Wall
The wall is thinned by squeezing the clay between a surface of each
hand and moving the hands (and thus the clay) upward while squeezing.
You can pull clay from the outside, inside, or both sides of the clay
wall, but pulling from both sides produces the best results.
Customarily, the distance between your hands remains constant
throughout each pull. This practice avoids the thick lower wall and
thin upper wall typical of the beginner's ware. Some professionals
keep the lower portion of the ware thick (for support) until the last
few pulls when the walls are evened. Regardless of your preferred
method, the distance between your hands must be shortened for each
pass (meaning one pulling action from bottom to top of the form). This
thins the wall further each time.
Common pulling surfaces include knuckles, fingers, sponges, wood ribs,
or the flat of the hand. Each surface has advantages and
disadvantages which are learned through experience.
* The knuckle is a stable and powerful surface which is especially
suitable for the first outside pulls.
* A finger (usually braced with other fingers and perhaps the
thumb) provides a low-friction exterior surface suitable for pulling
and thinning walls; it is also the most common pulling surface inside
the cylinder.
* A sponge reduces friction whether inside or outside the wall and
may require much less water for lubrication.
* A wood rib is somewhat limited but is significantly helpful for
straightening the inside or outside surfaces and eliminating ridges
left by the fingers or knuckle. It is important that the contact
surface of the rib faces in the direction of wheel rotation to avoid
digging into the clay.
* The flat of the hand is a relatively specialized pulling surface
because of its surface friction. However, it is quite useful outside
the wall when a large cylinder is in the early stages of development.
It is best that you develop a comfortable and personal style for
pulling, according to your strength and sensitivity to the clay. Don't
hesitate to try new methods, particularly those presented by more
experienced potters.
As a starting point, here is one example of a typical progression
through the pulling cycle: In the four o'clock position, at about 120
rpm, the first pull is made with the knuckle or fingers squeezing from
the outside of the walls and the fingers squeezing from the inside
(when the height of the wall permits, it is extremely helpful to brace
the left thumb on top of the right hand to strengthen and steady the
upward pull of the hands). The second pull repeats the first, except
the wall is thinned more by slightly decreasing the distance between
the fingers of the right hand and the fingers of the left. On the
third pull the shape begins to develop from the basic cylinder. The
fourth pull repeats the third, and the shape is completed. Throughout
the four pulls the wheel speed slowly decreases to about 70 rpm. Never
pull past the lip of the form. Always stop the pulling motion at the
lip or slightly below the lip to prevent over-thinning of the rim.
Sightly compressing the rim after each pull with a thumb or finger
helps to strengthen both the rim and the walls.
The specific speed of rotation during pulling is as varied as potters'
styles. The forms that defy centrifugal force (bowls) require slower
speeds than forms which are more vertical (bottles). Regardless of
the shape, most forms require a gradual decrease in speed throughout
pulling. Rotation must be fast enough to allow the potter to pull the
walls quickly but not so fast that it dictates shape. Through practice
you will learn to balance wheel speed, the speed of pulling, and the
amount of pulling force applied.
Hints for Successful Pulling
* Keep the clay evenly lubricated throughout the process by
periodically squeezing water onto the form from an elephant ear sponge
or using the sponge over your fingers on the outside of the pot.
* Although lubrication is essential, the less water you use when
throwing, the more strength and support the clay will have. There are
structural limits to the support clay provides. Water, basic clay
formation, centrifugal force, and the shape of the ware will all
determine whether or not your pot will be successfully completed. If
water begins to build up in the bottom of the form, use a damp sponge,
inserted into the opening as the wheel turns, to absorb the water.
Shapes thrown on the wheel consist of walls which are vertical or
walls which move out or in from the vertical plane. Learning to move
clay in these directions will help you throwing various shapes.
Pulling and collaring are the methods of directing clay. Generally
speaking, collaring moves clay in; pulling moves clay up or out.
Collaring
Collaring is the term applied to centering or reducing diameter of the
form after opening. The hands collar in the same manner as centering
- passing over the outside of the walls and squeezing them inward from
the bottom to the top of the desired area. To avoid twisting and/or
rippling, collaring must be progressively more gentle as the wall
becomes thinner. After collaring, the form may require an additional
pull because constricting usually thickens the clay.
Slight inward and outward movement, along with vertical directing of
the wall, are achieved by the position of your pulling surfaces and
the direction of the pull. When these forces cooperate, the clay will
generally follow. When they oppose each other, a pull may not increase
the height of the wall.
The interaction of pulling surface and pulling direction may be
illustrated using the knuckle of the right hand (outside the wall) and
the finger of the left (inside) as examples. When the knuckle is
above the finger, and the direction of pull is outward, the lower
finger should expand the form (if the pulling direction is away from
center, the finger provides most of the force). If the pulling
direction is inward, and the knuckle provides most of the force, the
form will tend to be collared. Thus there are two methods for pulling
the wall with vertically oriented pulling surfaces - either the wall
is moved directly in or out, or the wall is slightly stretched in the
opposite direction immediately before movement. If the pulling
surfaces are pulled upward at the same height, the wall will move
straight up.
Outward pulling direction tends to override the orientation of one
hand to the other. You will also find that thin walls are often more
difficult to constrict than thick walls. So if you are making tall
forms, maintain a constricted shape by periodically collaring
throughout the pulling process. If they are too thin, or if the clay
is overworked, some walls will not constrict.
Regardless of the direction the clay is moved, slow the pulling action
at the rim so you don't release the form too quickly. A speedy release
will throw the top of the form off center.
Troubleshooting
When learning to pull and collar, you may encounter some problems with
the clay. Hard lumps or soft pockets of clay, air bubbles, and foreign
matter (pieces of sponge, cloth, etc.) become more apparent and
problematic in the body as the wall is pulled thinner. If you find
such a defect, probe it with a needle tool to discover its composition
and size. You can usually lance an air bubble with the needle and
gently smooth it with your finger. Sometimes you can dig foreign
matter out of the wall and fill the hole with plastic clay. You can
also dig hard lumps or soft pockets of clay out of the wall and fill
the hole with new clay, but it is a better idea to re-wedge the clay.
When pulling, examine the throwing ridges (grooves left by the
fingers, knuckle, etc.) for evenness and spacing. Uneven ridges may
cause walls that are thick in some places and thin in others. Pulling
too quickly in relation to the wheel speed may form a spiral groove,
which is difficult to avoid in subsequent pulls. If pulling or
collaring pressure is too strong, the wall will twist or break off. A
twist can be corrected by gently applying pressure with a straight
finger on either side of the wall. An additional pull may also
straighten twists. If both of these methods fail, use a wood rib
inside or outside the form. Make sure that the clay is evenly
lubricated before applying pressure with the rib.
If you allow the twist in the cylinder to remain too long or it is too
severe, the form may slump or break during a pull. A wall that has
broken off should not be replaced on the form, but you can continue
throwing with the remainder of the clay; or a new hump can be centered
and pulled.
Collaring too quickly, or collaring overworked clay, produces a ripple
in the rim that can be eliminated using the steps to correct a twisted
wall.
If too much time is taken for the pulling process, if too much water
is applied, or if the walls are too thin to support the shape, the
form will sag or split. If this occurs, you will have to remove the
clay from the wheel head and re-wedge it. Do not try to use the same
clay more than twice during one session, because clay becomes too wet
and loses much of its plasticity as the clay particles break down.
If the rim becomes uneven from improper centering or opening, from
extensive collaring, or if the form breaks off, it should be evened by
cutting with the needle tool as the wheel rotates. Cut enough clay to
completely level the rim, because an uneven lip will throw the form
off center and will require further trimming. If the rim is only
slightly irregular, cutting may not be necessary. Instead, exert
pressure from the finger of the right hand to the rotating cylinder
while supporting the rim with the fingers and thumb of the left hand.
Completing the Form
When a successful form is pulled, it is completed with refinements of
the lip (also called the rim) and removal from the wheel head. During
both of these activities, speed of rotation varies according to the
stability of each shape thrown - greater stability allows faster
rotation. Horizontal ware, such as bowls, will require a considerably
slower speed. Fifty rpm is a starting point to experiment with for
slow rim refinement.
Refining the Rim
Once the shape of the rim is defined, it is finished with a wet
chamois, a wet sponge, or a lubricated finger. The finishing action
leaves a smooth clay surface and may also make subtle adjustments in
lip thickness and shape. Uniform lubrication is important for
maintaining a centered rim during finishing.
Cutting from the Wheel Head
When you are satisfied with the completed shape, cut it from the wheel
head or hump. Throwing all ware on bats will temporarily avoid the
problem, but you will eventually need to learn to lift ware from the
wheel head to develop full use of your throwing skills.
Most potters undercut the outside bottom of the wall before slicing
below the base. The undercut provides a ledge that helps you lift the
form and may also serve to complete the base if you don't want a foot
rim. To undercut a form:
1. Slowly guide a lubricated wood tool or pencil into the rotating
clay, beginning at a point which corresponds to the inside bottom of
the pot. With practice, you will be able to determine the proper point
of entry for undercutting by simultaneously sighting the inside bottom
and the point of the wood tool.
2. Line up the two on a horizontal plane, using simple depth
perception, and allow the point of the tool to make gentle contact
with the wall. Cut a shallow incised ring around the outside base.
Use the ring as a guide for starting the undercut. The cut is made at
a 45 degree angle.
Note: Be careful to keep the tool in its original groove rather
than cutting a
number of incisions; holding the tool with two hands will help to
steady it.
To cut the form from the wheel head:
1. Pass a tightly stretched wire (string or fishing line may also be
used) under the ware at the bottom of the undercut. Production
techniques usually require that this action be performed while
the wheel rotates, but it may be easier for beginners if the wheel is
stopped. In another version of the cutting technique, string is laid
against the bottom of the undercut while the form slowly rotates.
2. When it encircles the pot, pull the string. The wheel's rotation
helps cut the ware free.
Regardless of the method employed, all cutting motions should be
strictly horizontal to avoid a foot which is thick on one side and
thin on the other.
If the wire accidentally cuts a hole through the base, it is possible
to force the cut together again with throwing pressure on the inside
bottom of the form. Then another lower cut can be made with the wire
if there is enough clay for a base below the form.
Remove completed shapes after successful cutting. You may use your
fingers, manufactured or homemade pot lifters, or, if the shape has
been dryly thrown, you can use the flat of your hands (as if warming
them on a coffee mug). Horizontal or unstable forms which are thrown
on bats are cut and left to firm before removal. With practice, you
will be able to cut stable, small- or medium-sized forms as the wheel
turns, otherwise, a gentle twist frees the form from the stationary
wheel head.
When the form has been lifted to a ware board for drying, you can
correct any warpage by exerting pressure at the base of the elongated
axis. This forces the walls and rim back to the original circular
shape.
If you feel like a throwing problem cannot be solved, keep practicing.
Learning to throw involves reaching occasional plateaus where there
may be an almost complete lack of progress, but these periods will
pass. Practice and observation are the keys to throwing skill.
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