Fig. 17.Fig. 17.Wheel head with detached bat.
Fig. 17.Wheel head with detached bat.
Throwing is not an easy operation to describe but the following instructions in the form of lessons will, with a large amount of practice, enable the student to become fairly expert. Every opportunity should be taken to watch a good potter at work. There are a thousand and one little tricks in the position of the arms, hands, thumbs and fingers which are impossible to describe but which can easily be copied. If a kick wheel be used some time must be given to practicing the motion without using clay. The action of the foot must become subconscious or automatic like the pedaling of a bicycle so that simply to will a change of speed is to accomplish it.
Fig. 18.Fig. 18.The progress of a clay ball on the wheel.
Fig. 18.The progress of a clay ball on the wheel.
Lesson I.Take the bat about to be used, plunge it in clean water and soak it nearly, but not quite, tosaturation. If the bat remain wet one minute after being taken from the water, it has soaked too long and must be dried off a little. The effect of a wet bat is that the clay slips and cannot be held in one place. The proper dampness is secured when the clay ball can be pushed along the surface of the bat but does not slip easily. This condition is important and should be secured by experiment, because if not right, good work will be impossible.
PLATE I.PLATE I.Throwing.—LessonII, 1.
PLATE I.Throwing.—LessonII, 1.
PLATE II.PLATE II.Throwing.—LessonII, 2.
PLATE II.Throwing.—LessonII, 2.
Lesson II.Place a small basin of water close at hand. Take a ball of clay about three inches in diameter. Set it on the center of the wheel as nearly as can be judged. Now spin the wheel at a fairly rapid rate. Brace the left elbow against the side and, wetting the hand, press the ball of the thumb and the lower part of the palm against the clay. The leftforearm being kept rigid, the clay as it revolves will be forced into the center of the wheel. Use the right hand to sprinkle water on the clay that proper lubrication may be maintained. With the fingers of the right hand pull the clay towards you, at the same time pressing inward with left hand and so squeezing the clay. As the hands come together the clay will rise in a cone. Do not pull it upwards but let it rise as it is squeezed. Now bring the hands over the top and with the thumbs together press down again. Lumps and irregularities will be felt in the clay and the operations of spinning up and pressing down must be continued until these disappear. Repeat the exercise of centering with a fresh ball of clay until it can be accomplished with ease and rapidity. The clay so used is not wasted. The superfluous water may be dried off upon a plaster bat and the clay wedged up for use again.
PLATE III.PLATE III.Throwing.—LessonII, 3.
PLATE III.Throwing.—LessonII, 3.
This wedging or waging of clay—the word has descended from the old English potters—is important. A strong table should be built of which the top, measuring about 30 by 20 inches, is made of two-inch plank. A raised edge two inches high is fastened firmly by being nailed to the sides; the trough thus formed is then filled with plaster and allowed to harden. An upright post is fastened in the center of one side and from the top of this a fine brass wireis stretched to the other side of the table, thus making a diagonal. The worker stands at the side of the table opposite the post. The ball of clay is taken in both hands and cut in two against the wire, then the pieces are slapped smartly upon the plaster, one on top of the other. The whole lump is then lifted, cut in two and slapped down as before. The lump of clay is thus formed into layers, the irregularities in hardness are corrected and the clay made smooth. A little practice will make the work quite easy but it will often be found necessary to cut and beat the clay fifteen or twenty times before a good texture is secured. If the plaster table be dry the clay will be stiffened rapidly but the plaster may be made wet to prevent this if it should not be necessary. A clay may also be softened in this way by sprinkling it with water as the wedging goes on.
PLATE IV.PLATE IV.Throwing.—LessonIII, 1.
PLATE IV.Throwing.—LessonIII, 1.
PLATE V.PLATE V.Throwing.—LessonIII, 2.
PLATE V.Throwing.—LessonIII, 2.
Lesson III.Center the ball as in Lesson II and moisten both hands and the clay. Grasping the clay lightly but with sufficient force, press the right thumb downwards and towards the palm and a cup-shaped hollow is formed in the clay. Raise the right hand slowly, still keeping a light pressure upon the clay with the thumb. The clay wall will rise with the hand. Now insert the two first fingers of the left hand into the hollow and hold them against the right-hand wall. Slacken the speed of the wheel a little. Bend the forefinger of the right hand and press thesecond joint and the knuckle against the outer wall so as to oppose the fingers which are inside. Press the thumbs together to steady the hands and raise both hands upwards together. The fingers inside and outside the clay should be kept at a definite distance apart so that as the hands rise, the clay is brought to a uniform thickness. The hands are brought steadily to the full height to which the clay will go and thus a cylinder is formed.
Repeat this lesson three or four times with fresh clay.
PLATE VI.PLATE VI.Throwing.—LessonIV, 1.
PLATE VI.Throwing.—LessonIV, 1.
PLATE VII.PLATE VII.Throwing.—LessonIV, 2.
PLATE VII.Throwing.—LessonIV, 2.
Lesson IV.Keep the hands wet. Shape the clay cylinder as directed in the previous exercise. Now repeat the action of the fingers inside and outside and, beginning at the bottom, take a closer grip of the clay and draw up the walls as before. The cylinder is now taller and the walls thinner. Do this again and again taking a little closer grip each time until the cylinder is as tall and as thin as the clay will bear. The walls will probably spread as the work proceeds and the hands must then be used outside. Grasp the clay with both hands and squeeze it slightly; at the same time raise the hands upwards. This will reduce the diameter of the cylinder and thicken the walls. The operation of the fingers can then be repeated until the full height is reached. There is, of course, a limit to the height of the cylinder which can be made from a given lump of clay and it is bestto begin on a small scale. A ball of clay which can be easily grasped with the hands is the proper size with which to learn. A very small ball is nearly as hard to work as a large one. Repeat this lesson until a tall cylinder can be made with ease and certainty.
PLATE VIII.PLATE VIII.Throwing.—LessonV.
PLATE VIII.Throwing.—LessonV.
Lesson V.Keep the hands wet. Spin up a cylinder with thick walls as in Lesson III. With the fingers of the one hand inside and those of the other hand outside, open the cylinder gradually. Keep the wheel at a slow speed. If the edge runs unevenly, use both hands outside to steady it, then work outwards again until a shallow bowl is formed.
PLATE IX.PLATE IX.Throwing.—LessonVI, 1.
PLATE IX.Throwing.—LessonVI, 1.
Lesson VI.Keep the hands wet. Spin up a cylinder of medium height as in Lesson IV. With the fingers of the right hand outside press inwards at the base of the cylinder close to the bat and with the fingers of the left hand inside, press outwards at a slightly higher level. This will reduce the diameter at the bottom and increase it in the middle, making a cup shape. Now raise the right hand and gently draw the top inwards. With the left hand inside press the upper edge outward and with the fingers of the right hand shape the upper part into the form of a jar or flower pot.
PLATE X.PLATE X.Throwing.—LessonVI, 2.
PLATE X.Throwing.—LessonVI, 2.
PLATE XI.PLATE XI.Throwing.—LessonVII.
PLATE XI.Throwing.—LessonVII.
Lesson VII.Keep the hands wet; proceed as in Lesson VI. Instead of making the top flange outwards, draw it gradually inwards into a globe form. Work the clay carefully upwards and inwards untilthe opening at the top is almost closed. Several attempts will probably have to be made before this result can be secured.
PLATE XII.PLATE XII.Throwing.—LessonVIII, 1.
PLATE XII.Throwing.—LessonVIII, 1.
Lesson VIII.Keep the hands wet. Spin up a globe shape with a narrow base as in Lesson VI but carry a good share of the clay to the top so that the upper edge of the globe is quite thick. Insert two fingers of the left hand and with the fingers of the right hand outside work the upper edge of the globe into a tall neck. The action is the same as in the shaping of a cylinder except that the diameter is smaller. A good deal of practice will be necessary in order to keep the neck thin and to raise it to any appreciable height, but perseverance will accomplish it.
PLATE XIII.PLATE XIII.Throwing.—LessonVIII, 2.
PLATE XIII.Throwing.—LessonVIII, 2.
These lessons if carried out conscientiously will enable the operator to produce almost any form in so far as the manipulation of the clay is concerned but the work up to this point is drill only. It is not intended that the pieces should be preserved. The next point is to insist that the clay obey the potter in the shaping of a form.
A simple drawing of a jar should be made exact to the size proposed. Two or three pairs of calipers are provided and with them the diameter of each part of the drawing is taken. Of course a single pair could be made to serve, but it is very inconvenient to change measurements while working. A piece of wood also is cut to the height of the proposed piece.The throwing is begun as usual by making a cylinder. This should be higher than the drawing for the clay sinks in the shaping. First the bottom is pressed into the proper size (Lesson VI). Then the body is enlarged to the required measure and, lastly the diameter of the top is taken and the height brought to the determined point. If too high the superfluous clay may be cut off with a pointed knife, the edge being carefully rounded afterwards.
It is only by checking up one's work in some such way as this that real power can be acquired. The skilled worker can think in the clay and create forms at will upon the moving wheel, but for the beginner to attempt this is like an endeavor to paint pictures before one has learned to draw. Shape after shape should be designed, drawn to scale and thrown to measure; in fact, for elaborate pieces no other course is possible.
It is not possible to finish work to perfection in the operation of throwing. The clay is too soft to handle and for proper finishing the piece must be turned over to get at the bottom. An experienced thrower reduces the final work to a minimum and this, of course, is the ideal plan but even in factory practice every thrown piece is passed on to the turner so that the phrase "thrown and turned" is used as of a single operation, though it, in fact, expresses not only two processes but the work of two men.
The artist-potter must needs, therefore, learn to turn, though this process should not be worked to death as it is liable to be. Many persons in the pride of having produced some sort of a form on the wheel will leave it in the crudest possible condition and trust to the turning tool to remove defects. If the lessons on throwing have been conscientiously carried out, this error will not be committed.
A half dozen cylinders of convenient size should be thrown on separate bats and set aside in a cool place to harden. They must not be dried but shouldbe in the condition known as "leather hard." If thrown one day they will be ready for turning the next morning. Pieces thus hardened are no longer flexible. They can be handled freely and the clay can be easily cut with a knife.
Fig. 19.Fig. 19.Turning tools bent and sharpened.
Fig. 19.Turning tools bent and sharpened.
The equipment for turning consists of a board support, a turning stick and a set of tools. The board is of soft pine, eight or ten inches wide and two feet high and is set upright at the back of the wheel frame opposite the workman. It may be screwed in position if it does not interfere with the throwing, or it may be set in a socket so as to be removed when notin use. Its purpose is to support the end of the turning stick. The stick is an ordinary broomstick in the end of which is a sharpened nail. In use the end of the stick is held in the left hand and the point is pressed into the board at any required height. The right hand, holding the tool, is rested on the stick just as the hand of a painter rests on the mahl-stick.
The turning tools are of soft steel.[H]They are purchased unshaped and the potter must learn to bend and file them to suit himself. A section of bench should be set apart for filing and care must be taken that the steel dust does not get into the clay.
One of the cylinders, with the bat upon which it was thrown, is now taken in hand. Many beginners try to turn their pieces without detaching them from the bat, trusting to the original adhesion to hold the piece in position. This is a very unsatisfactory plan. A fundamental principle in craft work is that the mechanical difficulties in manipulation should be met and overcome at the first. If one trusts to some method which is apparently easy one walks with crutches and there will come a time, if progress is to be made, when such helps must of necessity be abandoned and then the learning must be begun again. Therefore the student is advised to face the mechanical technique at the very beginning. The cylindermay be turned on the throwing bat, but there is a better way.
The piece should not become so hard that it will release its hold on the bat but with a long bladed knife it should be cut away. If the knife be held close to the bat a separation is easily effected. Set the leather-hard cylinder upon a new bat which is slightly damp and which runs true, on the wheel. The first problem is to center the work. A pencil line may be run upon the bat making a circle just the size of the cylinder. Then as the wheel is revolved it will be seen if the piece runs true. It is quite unlikely that this will be the case. Perhaps the bottom is true but the top circle is untrue. In other words, the axis of the cylinder is not upright. Turn the cylinder upside down and try if it will run any better. If it does the work may be begun in this position. If it does not, turn it back again. Now take a pencil and hold it with a steady hand so that it just touches the near side as the wheel goes round. Lift up the edge of the cylinder on the side marked by the pencil and slip a morsel of clay under it. Revolve the wheel and try with the pencil again. In this way raise or press down one side, keeping the bottom circle in the center until both top and bottom are running as nearly true as they can be made. This, so far, refers only to the horizontal planes. If one side is higher than the other it does not matter at present. Nowtake three small pieces of soft clay, and, holding the cylinder firmly with one hand, press them down at equidistant points in the angle where the piece joins the bat. This serves to hold the work in position. A square turning tool of small size is the best to begin with. It is held in the fingers as a pen is held but more firmly. The right hand rests on the turning stick and, the connection between hand and stick being as rigid as possible, both are moved together. This is better at first than moving the right hand freely for to do so will surely result in irregular work.
The tool should be held so as to cut with one corner at first and it is well to take one cut, remove the tool, take another cut and so on. The object should be to feel the clay and to test its resistance. No one can be a successful potter who does not cultivate a sympathy for the clay. The tool is to cut, not to scrape. That is, the cutting edge is to be opposed to the revolving clay. The point at which the tool touches the clay is opposite the center or at the same distance from the operator as the center of the wheel is. If nearer to the workman the tool will not cut; if further away, it will scrape and pull (Fig. 5, page 50).
The first efforts should be directed towards acquiring skill. The student should endeavor to make a cut at any desired point without regarding the effect upon the shape of the cylinder. In other words the clay is used merely as a practice piece. It is notto be preserved. It is a good plan to keep on turning the first piece until it is all turned away. Too many students fail because they wish to have a piece to keep. He will make the best ultimate success who cares nothing for the preservation of a dozen or two cylinders or other shapes, but uses them merely as exercises in manipulation. If the student is over anxious to avoid spoiling his work, he grows nervous and so loses control of his tools and material. To set no value on the practice pieces themselves begets confidence and this is the surest aid to success.
After two or three cylinders have been centered to the pencil line the attempt to center one free-hand may be made. Place a cylinder on the wheel but not quite in the center. Spin the wheel at a medium rate. Fix the attention upon the eccentric motion, trying to forget the circular motion. As the cylinder appears to move from side to side tap it lightly with the hand so as to drive it towards the center. In all probability this will result in driving the cylinder off the wheel altogether. Some little practice is needed, but if persevered in the result will be a power of convenient and rapid centering which is never forgotten and which is the greatest possible help to successful work. One may practice with a wooden cylinder or even a tin can if the weight approximates that of the clay pieces.
Fig. 20.Fig. 20.Turned feet.A B C, feet for small pieces.D E F, feet for large pieces.G H I, common faults in foot finish.
Fig. 20.Turned feet.A B C, feet for small pieces.D E F, feet for large pieces.G H I, common faults in foot finish.
Accompanying the practice in turning there should be some exercise in the shaping and filing of tools. Broad tools filed to the proper curve are indispensable in finishing concave surfaces. A curved edge may also be put upon one or two narrow tools. These will cut more rapidly than the broader ones but will not leave as smooth a finish. Whatever tool be used the final surface must be worked over with a soft sponge and water so as to eliminate the tool marksand leave a plastic surface. One of the principal troubles with which the beginner will meet is the vibration of the tool known as "chattering." This is sometimes so slight as not to be felt by the hand but when the motion of the wheel is stopped the work will be found covered with fine ridges like gathering on muslin. The way to prevent this is to avoid using the broad edge of the tool until some experience has been gained. The way to cure it is to go over the work again with a fine pointed tool and then to use the sponge liberally. The point of the tool cuts through the small ribs or wrinkles whereas a broad tool would ride over them and make the trouble worse.
While the whole surface of the work will probably need more or less turning, the chief part of the operation is concerned with the under part or foot. The formation of a good foot marks a good potter and vice versa. Before beginning to turn it should be decided what kind of a foot is desired. Each shape has its own style. Some sketches are given here with an idea of the form to which each is adapted. They are shown upside down because the work is done in this position. The small bevel at the outer angle is used for facility in glazing. A foot finished thus always has a neat appearance when the glaze has been removed from the beveled face.
There is a limit in size beyond which the non-professional will not be able to go. Men of life-long experience can throw very large jars but this involves not only more practice than the artist-potter can hope to secure but also great physical strength. On the other hand it is perfectly possible to form vases two or three feet in height by doing the work in parts or sections. No one need fear to put such a plan in operation on account of sentiment. It is, of course, worth while to make large wares in a single piece but section work involves great skill and, as a rule, the result attained is better. Work made in one piece is apt to be badly finished, especially inside, and unduly heavy. Work made in sections can be thrown with thin walls and finished with proper care. If tradition be of any help, be it known that the Chinese have used the piece method for hundreds of years, and that the Greeks used it three thousand years ago.
The first requisite is a drawing either actual size or properly scaled. The measurements should bethose of the soft clay and if a particular size be desired in the burned piece, the shrinkage, probably about one-eighth, must be added. The drawing must show the size of each section with the points of junction, and should indicate the upper and lower edges in each case. Some divisions are best made right side up; some are more easily thrown upside down. Care should be taken that the faces which are to be joined are thrown under similar conditions. In every piece of work one face rests on the bat, the other is in the air or free. A bat face should always be joined to a bat face and a free face to a free.
Suppose, for instance, a vase is to be sixteen inches high and is to be thrown in four divisions of four inches each. The bottom division is made first. This will stand in its normal position, right side up. The second section must now be thrown upside down, because, if it were not, its bat face would be joined to the free face of the first piece. So the sections are thrown alternately, every other one being inverted.
PLATE XIV.PLATE XIV.Making Large Pieces. The First Section.
PLATE XIV.Making Large Pieces. The First Section.
As the pieces are thrown they must be carefully measured to see that the faces which are to be united are the same size. The height of each piece also must be gauged and adjusted. The bats with their contents are now set aside to harden. As soon as they can be handled with safety the clay pieces should be removed from the bats upon which the throwing was done and set upon dry bats which will absorb themoisture and help to stiffen the clay. It is a good plan to pile the sections up as they are to stand in the finished piece, one upon another and to leave them so in a cool place for ten or twelve hours. The faces which are to be joined will thus acquire a uniform hardness and unequal shrinkage will be avoided.
When all is ready for the turning, the sections being of the proper hardness are taken in hand. This work should not be hurried. It will take a whole morning to put together a large piece. First, the bottom section is placed on the wheel, centered and made to run true as regards the top edge. It is then inverted and the foot is properly finished, signed and dated. Then the second joint is likewise turned true on both faces, the inside turned smooth; and so on, each piece in turn is prepared for the fitting, the measurement of each face being accurately adjusted. At this stage it is possible to correct the diameter of the faces to some extent either by pressure as the wheel revolves or by building up with soft clay. In either case, however, the new work must be hardened before proceeding. The whole piece is now put together carefully but with dry joints. It should be slowly revolved on the wheel and the proportions carefully criticised. If satisfactory it is taken apart again and the actual fitting up may proceed.
The bottom section is again centered most carefully on the wheel and steadied with three pieces ofclay. A thick slip is now prepared, the same clay as that used for the work being of course, used. This slip must be quite free from lumps and should be as thick as molasses. The upper edge of the work is carefully sponged with clean water and a good coating of slip is applied at the junction. Care must be taken that every part of the face is covered with slip. The second joint is now moistened at the junction and set in position upon the bed of slip. It is placed very lightly and the wheel is gently revolved to see if the running is true. If so it is pressed home and the superfluous slip is removed. The joint should be quite close like a glued joint in carpentry.
In the same way the third section is placed upon the second and the fourth upon the third. It is now possible to work over the face of the vase with a little soft clay. There is almost always some irregularity in the line, especially at the joints, and this must be adjusted while the work is moist. Then the whole face is gone over with turning tools and sponge and the vase is set aside to dry. It must not be expected that large pieces, made by any method, will be produced with as much ease as small vases and bowls. The risks are much greater and, owing to the size of the work, the faults are much more apparent. When the vase is perfectly dry it should be set on the wheel, centered and slowly revolved. If it is very untrue in its motion there is no remedy. Itshould be broken down and the clay used again. A very slight irregularity may be corrected by rubbing off a little clay on one side of the foot but this cannot be done to any considerable extent. The courage to break unsatisfactory work is never more valuable than at this juncture. It will pay in the end, for no imperfect piece can be a source of satisfaction to the conscientious craftsman.
PLATE XV.PLATE XV.Making Large Pieces.Measuring the Foundation of the Second Section.
PLATE XV.Making Large Pieces.Measuring the Foundation of the Second Section.
PLATE XVI.PLATE XVI.Making Large Pieces.Drawing up the Second Section.
PLATE XVI.Making Large Pieces.Drawing up the Second Section.
PLATE XVII.PLATE XVII.Making Large Pieces.Shaping the Third Section.
PLATE XVII.Making Large Pieces.Shaping the Third Section.
PLATE XVIII.PLATE XVIII.Making Large Pieces.The Three Sections Completed.
PLATE XVIII.Making Large Pieces.The Three Sections Completed.
PLATE XIX.PLATE XIX.Making Large Pieces.Turning the Edge of the First Section. (Note the other sections on the table.)
PLATE XIX.Making Large Pieces.Turning the Edge of the First Section. (Note the other sections on the table.)
PLATE XX.PLATE XX.Making Large Pieces.Finishing the Bottom of the First Section. (Note the second section in the foreground ready for turning.)
PLATE XX.Making Large Pieces.Finishing the Bottom of the First Section. (Note the second section in the foreground ready for turning.)
PLATE XXI.PLATE XXI.Making Large Pieces.Checking the Size of the Second Section.
PLATE XXI.Making Large Pieces.Checking the Size of the Second Section.
PLATE XXII.PLATE XXII.Making Large Pieces.Fitting Together Dry.
PLATE XXII.Making Large Pieces.Fitting Together Dry.
PLATE XXIII.PLATE XXIII.Making Large Pieces.Setting the Third Section in Place.
PLATE XXIII.Making Large Pieces.Setting the Third Section in Place.
PLATE XXIV.PLATE XXIV.Making Large Pieces.The Three Sections Set Together in the Rough.
PLATE XXIV.Making Large Pieces.The Three Sections Set Together in the Rough.
PLATE XXV.PLATE XXV.Making Large Pieces.The Finished Vase.
PLATE XXV.Making Large Pieces.The Finished Vase.
It is not likely that many craftsmen will care to produce table wares or even that they will be able to acquire the necessary skill. Simple as these wares seem, they are, in fact, the most difficult of all to make well. In factory working, one man makes nothing but cups, another saucers and another plates, so that each attains the skill of constant practice, but this is out of the question for the studio worker. At the same time it is well to know how it is done and it may be that some one will undertake to produce a few pieces for the sake of the enjoyment arising therefrom.
It is possible to finish a cup upon the wheel just as a vase is made. The handle is modeled in clay and fastened in place with slip when in the leather hard condition. Saucers and plates cannot be made in this manner; first, because the broad thin bottom will surely crack and, second, because it is impracticable to turn a plate or saucer over in order to finish the bottom. The risk of breakage is so great that there is nothing to be gained.
If cups be needed of uniform size they must be molded. The making of the molds has already been described. A small cylinder of the proper size is thrown in clay and removed from the wheel while soft. A number of these should be made at one time so as to avoid changing the wheel head often. When all are ready a hollow head shaped to receive the cup mold is set on the wheel and a mold inserted. One of the soft cylinders is now lowered gently into the mold and as the wheel is revolved the soft clay is pressed firmly against the walls with the fingers. A piece of wood, called a rib, cut to the exact shape of the inside of the cup, is used to smooth off the interior. The top edge is cut off and rounded and the mold is set aside for the cup to harden. As soon as the cup can be turned out it is set upside down upon the wheel and the bottom turned.
Another method dispenses with the formation of the cylinder or "lining." A ball of clay of the proper size is dropped into the mold and pressed into shape with the fingers, the wheel, of course, being spun. The finishing is accomplished with the rib as before. This method will answer for wares which are to receive a low fire but for high temperatures the clay must be handled by the first-named plan.
The cup is not complete without a handle. This may be modeled as already stated but to make eachone of half a dozen in this way is unduly tedious. The better plan is to model a handle in wax and make a mold as already directed. A roll of soft clay is then laid in the mold, the two halves pressed together and the handle taken out and finished. Care must be taken that cup and handle are of the same degree of moisture, leather hard, for choice, or they will part company as they dry. The fastening is done with thick slip.
The method for saucers is the same as that for plates, so that one description will suffice. The first step is to make a tool or profile. A large handful of soft clay is rolled out into a thick cylinder and laid down upon the plate mold. It should extend from the center to the circumference, forming a radius of the circle. The clay is pressed closely to the surface of the mold and part of it is squeezed into a knob which will form the hand-hold of the tool (Fig. 16, page 66). The clay is left in this position until it becomes nearly but not quite dry. It is then taken off and whittled into shape. The front edge must be straight and must lie along a radius of the plate. The foot is cut in at the proper point and a broad wedge-shaped hollow is made so as to gather the clay and pile it up into the foot. The hand-hold is shaped so as to fit comfortably between the first and second fingers of the right hand. When properlyshaped the tool is thoroughly dried and then burned in the kiln. The fire must not be severe as it is important not to shrink the tool to any great extent. After burning slight corrections can be made with a file or a hard stone. The heel of the profile must be exactly at the center of the plate and the toe or curve must rest on the outer edge of the plate mold.
In making plates a "batting block" and "batter" are used. The former is a heavy block of plaster which is fixed to a strong table. It must be saturated with water when in use. The wedging table already described will serve for this. The batter is a disc of plaster to which a handle is attached. It may be made of a thick plaster block, the handle being cut out of the substance itself. This is also kept saturated with water so that the clay will not stick. A ball of clay is laid on the block and gently beaten out with the batter into a disc of the proper size and thickness. The face of this is then polished with a steel blade and the disc is then lifted, turned over and laid, polished side downward, upon the mold. The wheel is then revolved and the clay pressed firmly to the mold with wet hands. The tool is now dipped in water and pressed steadily upon the revolving clay. The heel must be adjusted accurately to the center and the foot will be seen to rise up in its proper place. The operation is not easy and many failuresmust be expected but practice will accomplish the desired result. When leather hard the plate is gone over with a thin piece of rubber and when quite hard it may be removed from the mold. The edge is now trimmed and the face sponged over and the plate is ready for the kiln.
In commercial production the casting method is constantly used. It is a means of making light and delicate pieces with ease and, of course, all the pieces cast in the same mold are alike. This very fact, however, has led to the method being disregarded by the studio worker who does not wish to duplicate anything that he makes. If a single piece only is to be made the work involved in molding is a waste of time and it is better to strive for skill at the wheel, and yet there are occasions when a knowledge of casting is of great value. In the preparation of trial pieces there is no method better. To make these in sufficient number on the wheel would be tedious except for the benefit of the practice involved.
Directions for making molds have already been given and the slip which will have been prepared in the process of clay making is ready for the casting process. This slip should be thick, about the thickness of buckwheat batter. To be accurate, a pint should weigh 26 ounces. For small pieces or for vases with narrow necks it is advisable to use theslip rather thinner. For large wares, on the other hand, or for open bowls it may be slightly thicker. A few experiments will show the reason for this. Two quart jugs are needed. They should be large of neck and should deliver their contents freely and completely. Jugs with a deep shoulder are not good as the slip hangs in the pouring. One of these jugs is filled with slip which is to be poured carefully from one to the other, allowing it to flow gently down the side. This is to break the air bubbles which are nearly always found to be present and the pouring should be repeated until the slip flows smooth and even.
The mold, being thoroughly dry, is tied around with twine, if in parts, and wedged firmly so that it cannot leak. The slip is then carefully poured so as not to touch the sides and the mold is filled until a small mound of slip rises over the edge. This mound will at once begin to sink as the water is drawn into the walls of the mold and slip must be added, little by little, to make good the loss. A small quantity of clay will now be found to have stiffened at the rim of the mold and if this be carefully removed with a steel tool the thickness of the wall of the vase will be seen. If not thick enough the mold must be continually filled up until the necessary thickness is attained. The mold is then carefully lifted, making sure that the bottom is held firmly, and the slip is poured out. Itshould not be poured back into the casting-jug but into another vessel.
The mold is now set upside down to drain. It should not be placed upon the table but upon two sticks laid parallel so that the drip may hang clear. Several molds may be filled in this way at one time and after about twenty minutes the one first filled may be opened. The bottom is gently detached and the upper part of the mold, consisting of two halves, is laid upon the table on its side. A little gentle manipulation will now suffice to lift the one half and the vase will be seen lying in the other half as in a cradle. The clay is still very soft and must be treated carefully. The half mold, with the contained vase, is taken in the left hand and held nearly upright, the fingers below, the thumb on the top. Now set the fingers of the right hand under the bottom of the vase, rest the thumb lightly against the side and tilt the half mold gently forward. If mold and clay are in good condition the vase will fall forward to be supported on the fingers of the right hand and steadied by the thumb. The half mold is now laid down and the vase taken in both hands, set gently on a plaster bat and put aside to dry. It often happens that the vase leaves the mold with reluctance. If the slip be very new, or the mold either damp or hard or worn out there will be some difficulty in effecting a separation. By allowing the work to stand a while, however,and by slightly jarring the mold from time to time with the ball of the thumb the piece can generally be removed without damage.
In using a new mold it is customary to make what is called a "waste filling." The mold is filled with slip and at once emptied. After standing a few minutes it is forcibly opened and the thin layer of clay inside is picked out with a ball of plastic clay pressed against it. A tool should never be used as this will damage the face of the mold. If the clay should stick obstinately a soft cloth used over the finger will remove it. The reason for this waste filling is that it removes the scum which occurs on all new molds.
Cast ware should not be touched until quite dry and then the spare at the neck is carefully cut off, the seams scraped down and the whole surface smoothed with fine sand paper and a soft cloth. Worn out linen serves excellently for this purpose.
Cups and bowls, if molded, are made without spare at the top. In this case great care must be taken to see that the edge is left clean and smooth in the casting. The spare neck on a vase acts as a margin of safety, as it is completely cut away in the finishing. If a piece has no spare the edge must be left without blemish at the first.
There are two methods of making tiles, the dust-pressed method and the plastic. The former is the more usual commercial plan but the appliances for preparing the dust and the heavy presses necessary are not adapted to studio work. The dust-pressed tile is, moreover, somewhat mechanical in surface. It is not suitable for modeling or for any treatment but those of glaze and color. The plastic tile, on the other hand, may be treated by plastic methods and the surface offers a texture which appeals strongly to the artist.
For the successful production of tile a special body is necessary. Ordinary pottery clay is too close in grain and straight tile cannot be made from it. Small square pieces, however, such as tesseræ, can be made from any clay.
It is presumed that a pure white tile body is not required. For studio work the most pleasing white surface is found in an opaque enamel, but for the most part the craftsman will wish to work for colored tile. A cream or buff body is all that is necessary,therefore, and the foundation of this is a clay known as sagger clay. In order to secure the necessary porosity a fine "grog" must be used. Grog is burned clay. After working awhile there will be an abundance of this in broken unglazed pottery but at first some soft fire-bricks must be pounded. This is laborious work, but a boy can usually be hired to do it. The brick or broken pottery is crushed in an iron mortar but should not be broken too fine. Two sieves are necessary, one of 20 and one of 40 meshes to the linear inch. The coarse powder which passes through the 20 mesh and lies upon the 40 mesh is used. This is called 20-40 grog. The dust which passes through the 40 mesh may be saved for kiln work. It is useful for setting biscuit pieces one upon another as it will effectually prevent sticking. This powdered grog is also useful in the case of flowing glazes. A thick layer on the bottom of the kiln will catch any drops of glaze and save the kiln from damage.
A quantity of the 20-40 grog having been prepared, a mixture should be made of:—
The clay should be finely pulverized and the whole mixed in the dry state. Water is then added, littleby little, until a rather soft mass is obtained. It is not practicable to mix clay of this description by the slip method because the grog would settle out and fall to the bottom of the vessel. It sometimes happens, however, that the stoneware clay contains grains of iron which cause black spots to appear in the tile. If these cause trouble the clay must be made into slip first and lawned through 120 mesh. It is then allowed to become very thick and the grog is stirred in. This is a good deal more trouble than the first named plan and is not often necessary.
Tile are sometimes made in plaster molds. A tile of the proper size is cut from a plaster block and a mold is made from it. If a modeled surface be desired clay may be modeled upon the face of the plaster tile before the mold is made. The mold will then receive the embossment in reverse and all the tiles made from this mold will be alike. The clay is pressed into the mold while quite soft and is scraped off level at the back. Thus it is the face of the tile that is shaped by the plaster. If this plan be adopted the tile must be removed from the mold as soon as possible. If left to dry in the mold they will warp because of the unequal absorption.
A better method has been devised by the author and has been put into practice with considerable success. When the size of the proposed tile has been determined a board is made which is large enoughto hold a square of the tile, say twelve or sixteen. Thus if a tile five inches square is to be made the board would be fifteen by twenty inches for twelve tile or twenty inches square for sixteen. On each side of the board a wooden rim is fastened and this must stand higher than the board to the exact thickness of the tile. About five-eighths of an inch is enough. The board must be perfectly rectangular and marked off at even distance of five inches and a shallow groove is cut at each point.
To make the tile the board is wetted and an even coating of grog dust is sprinkled upon it. A ball of clay is laid in the center of the board and rolled out with a rolling pin to fill every part of the frame. With a straight edge the clay is struck off smooth and clean, working always from the center outwards. Reversing the plaster mold method the tile are now face upward and any kind of surface may be given at will. The clay may be lubricated with water and made smooth or it may be sprinkled with grog dust which will give a sandy or toothed finish. The square is now to be cut into tile and this is done with a slender knife and ruler. The ruler should not rest upon the clay but upon thin strips of wood or cardboard which may be laid along the edges for the purpose. The cutting should not go quite through the clay as, if a slight connection be allowed to remain atthe bottom, the tile will keep each other straight. When the cutting is finished the board should be set at an angle of forty-five degrees for the clay to harden. When leather-hard the whole may be turned gently over and the tile allowed to fall on to a board placed in readiness. They are now broken apart, trimmed if necessary and set aside to dry.
Tile made in this way can be kept straight without difficulty and the method is much more expeditious than pressing in plaster molds.
If a modeled surface be intended it is quite easy to work on the tile in the tray while the clay is soft. Forms may be cut in wood and pressed into the clay in any variety and the charm of individual treatment is preserved.
The body given above will prove quite porous when fired but it will take matt glazes well. A little crazing is no detriment to tile because they are not like vessels which are meant to hold water. If a denser body be wished for some of the flint may be replaced by spar.
One of the most attractive methods of decorating tile is by means of a white or delicately tinted enamel and color. The opaque tin enamel given on page 134 will answer well and if the whiteness prove too intense it may be modified by a very small addition of under-glaze color according to the tint desired. The tile should be glazed rather thick. Not as thick as a matt glaze but thicker than bright glazes. The glazeor enamel should be poured into a flat tray which is large enough to receive one tile. The tile is taken by the edges between fingers and thumb and held face downwards. Do not let either fingers or thumb project beyond the face. The glaze having been well stirred the face of the tile is allowed to rest upon it for about two seconds. The hand is then lifted quickly and reversed so that the tile is face upwards. Every effort should be made to avoid streaks or tears and a little practice will accomplish this. If the glaze shows a bad surface it should be scraped off. It can be mixed up and used again. Sometimes a slight wetting of the tile before glazing will help the surface to flow evenly.
The decoration is carried out with ordinary under-glaze colors. These may be mixed together to produce any hue which is sought and a little of the glaze itself, about ten per cent., should be mixed with the color. This will assist in uniting the color with the glaze so that they melt together.
To produce enamel decorations at their true value the color should be painted upon the dry glaze before it is burned. The best relation between surface and color is thus secured. The color must be worked quite thin with water and a little glycerine. A quick, sure stroke is needed as no change or erasure is possible. The design may be made on paper and traced or pounced on to the glaze with lamp-black.
For burning the tile there is nothing better than little fire-clay boxes. These can be made in a mold without difficulty and the inside of each should be washed with glaze. If some such protection be not provided dirt is almost sure to fall on the flat surface and the tile will be spoiled. It is not possible to rear them on edge in the kiln for burning as then the glaze would flow to the lower side and cause an unsightly ridge.
Much of the fascination of pottery making centers in the glaze. At one time a great deal of mystery appeared to surround the composition and use of glazes, but if one will take the trouble to learn, much of this may be dispelled. Some knowledge of chemistry is desirable if an understanding of the theory of glaze-making is to be acquired, but a good deal may be learned even without this knowledge. Only such simple instruction as can be assimilated by ordinary intelligence will be attempted here, as an exhaustive treatment of the subject would be long and tedious.
It is possible to purchase glazes ready for use[J]but the true craftsman will not be satisfied until he can prepare his own.
Glazes[K]belong to a class of chemical compounds known as silicates; that is, they have silica as the characteristic ingredient. Clear glazes are compound silicates of lead, zinc, lime, potassium, sodium, aluminum and boron. Matt glazes are characterized by certain of these ingredients being present in excess; and stanniferous or tin glazes are, as the name implies, rendered opaque by the use of oxide of tin.
The commonest type of glaze is that which is made from ready prepared, commercial substances. These are called raw glazes as being made from raw materials or materials which need no preparation.
It is possible to mix a glaze in a druggist's mortar by hand, using fine sieves, but if the best results are to be secured, a small mill must be used for grinding. The best form of mill is the ball mill or jar mill. This consists of a porcelain jar which is set in a frame and made to revolve upon its axis in a horizontal position. It is about half filled with porcelain balls and these as they roll against each other perform the grinding. These mills may be purchased ready for use, either as a single jar to be worked by hand or a battery of two or more revolved by power.[L]
A good pair of scales is a necessity and it will be found convenient to use metric weights which needno calculation into pounds and ounces. Suspended scales are not as easy to use as the form known as counter scales or balances. They should have movable pans which are usually nickel plated. Upon these the materials can be placed direct without the use of pieces of paper, which are always troublesome and inaccurate. There should be a graduated bar on the front for the adjustment of weights of five grams and under. This avoids the use of small weights which are always being mislaid and lost. Dealers in chemical supplies keep these scales in stock and the cost is about eight dollars. A set of weights must also be procured from one hundred grams to five grams inclusive. These need not be of the accurate adjustment which are used in analysis. A good inexpensive grade is sufficient.
The ingredients for glazes are given in the following list:
For coloring, the following metallic oxides are used:
Under-glaze colors may also be used for coloring glazes, the color being ground with the glaze batch.
It is not absolutely necessary to commit the formula and equivalent weight to memory. They will soon be remembered as use becomes second nature.
A glaze is usually expressed as the chemical formula. In this there are three divisions given, each of which expresses a distinct function. On the left hand are the bases, the foundation of the glaze. These indicate the type, such as lead glaze, a lime glaze, an alkaline glaze, etc. All glazes being silicates, this is the usual way of distinguishing them. In the center are the alumina and boron oxide. These regulate the behavior of the glaze in the fire. They make it viscous or sluggish as it melts and prevent a too rapid flow. The alumina is infusible, the boron is fusible, but boron cannot be used in a raw glaze for reasons to be presently explained. At the right stands the silica, the dominating factor with which all the other ingredientscombine, and which controls the behavior of the whole as regards the fitting of the glaze to the body.
The very simplest form of glaze is a bisilicate of lead, represented by the formula PbO, SiO2, or one equivalent of lead oxide and one of silica. The term "equivalent" means that the mixture is calculated, not upon the actual weight of a substance but upon its equivalent or unit weight. Thus the equivalent weight of lead oxide, PbO, being 222, in order to produce the formula in actual weight 222 grams or pounds must be weighed out. It does not matter what weights are used so long as they are the same for all.
In like manner the equivalent weight of silica is 60 and as flint is pure silica, the formula PbO, SiO2would be produced by weighing—
Litharge is not, however, a convenient substance to use. It is very heavy and does not mix well in water. The most usual substance for the introduction of lead oxide is white lead. This is not lead oxide but it changes to lead oxide when burned. White lead bears the formula Pb(OH)2, 2PbCO3, which, being dissected is found to be 3PbO, H2O, 2CO2. H2O is water and CO2carbonic acid, both of which pass off in burning. Both, however, are weighed when thewhite lead is put on the scales and therefore the equivalent weight of white lead is 258 and not 222.
The mixture for practical purposes then would be—
Which, when ground and spread upon the ware would be a very fusible glaze of a yellowish tone.
This was spoken of as a bisilicate of lead because the measure of the silica, also called the acidity of a glaze, is calculated upon the oxygen contained in the base and the silica respectively. PbO contains one molecule of oxygen, SiO2contains two. Hence the relationship of the oxygen in the base to the oxygen in the silica is as one to two. This is called simply the "oxygen ratio" and is of great importance in determining the behavior of a glaze. While this simple bisilicate of lead will be a glaze under certain conditions it is found to possess two faults. 1. It is too fluid under fire. The glaze will run down a vertical surface and leave the upper edge of the piece bare. 2. If subjected to a long slow fire it will lose its gloss and become devitrified. This devitrification is often seen in commercial work and appears as a dull scum in patches and around the edges of the ware. It is, in fact, a crystallization of the silica which separates out, as salt does from an evaporated brine. Both these faults may be corrected by the addition of a little alumina to the glaze. A whole equivalent of aluminawould be too much, in fact it is found in practice that .2 equivalent is sufficient for most lowfire glazes. In order to maintain the oxygen ratio and to keep the glaze as a bisilicate the silica content must be raised. Alumina contains three molecules of oxygen so that the total amount of alumina is multiplied by three and the silica brought to the equal point thus:
PbO, .2Al2O3, 1.6SiO2
The amount of silica required in any bisilicate glaze may be found by the following equation:
SiO2= 2(3Al2O3+ 1) / 2
Thus if the alumina content were .25 equivalent this would be expressed:
SiO2= 2(.75 + 1) / 2
Or—
SiO2= 3.50 / 2 = 1.75 equivalent
Now in order to produce this as a mixture it would be possible to introduce the alumina in the pure state, but pure alumina is expensive and clay which contains alumina is cheap so that clay is generally used to supply the alumina. Clay, however, contains silica as well, and therefore allowance must be made for this. On referring to the formula for kaolin, the purest form of clay, Al2O3, 2SiO2, 2H2O, it will be seen that there is twice as much silica present in equivalence as thereis alumina and therefore .2 kaolin will contain .2Al2O3and 4SiO2. Subtracting, then, the 4SiO2from the 1.6SiO2needed there will be 1.2 left to be supplied in the form of flint. The mixture therefore is—
This is a glaze of the same character as that first given except that it no longer flows unduly from the higher places nor will it devitrify in a long-continued fire. The alumina will have counteracted both these evils.
A glaze with only lead oxide as the base is not, however, desirable for general use. The color is yellowish and the lead oxide is apt to destroy the hue of any colors which are used with it. The available bases may be classified under three heads. 1. The metallic oxides, lead and zinc oxides. 2. The alkaline earths, the oxides of calcium and barium. 3. The alkalies, potash and soda. Barium oxide is not often used and soda cannot be used in raw glazes because there is no convenient substance which contains it. As glazes are always ground in water only insoluble ingredients can be employed without preparation. Potash is found in feldspar which is insoluble and while there is a so-called soda feldspar it can rarely be obtained of sufficient purity.
In arranging the bases with which to compose a glaze it is desirable to use one at least from each class, but it must be borne in mind that however many bases are introduced the total must always be unity. This unit is, for the sake of brevity, described as RO. For example the following groups may be set forth:
The reason for the unit rule is that if one formula is to be compared with another there must be a uniform basis upon which to work and, furthermore, it makes no difference whether the silica combines with one, two, three, or four bases, the chemical action is the same and, so long as the sum of the bases is kept at unity, the same amount of silica will be required.
If two glazes be taken as an illustration this will be made clear:
Both of these formulae are bisilicates and each being properly fired, will stand, without crazing, on the same body.
The use of the formula is to give an insight into the composition of the melted glaze. It takes no account of volatile ingredients or losses in the fire but for this very reason it must be translated into the substances to be weighed before use can be made of it.
Of the ingredients given on pages 142, 143, some contain but one item of the formula, others contain several, as in the case of kaolin already cited. Feldspar, of the variety known as potash feldspar and named by mineralogists, "orthoclase," is a very useful ingredient in raw glazes, being, in fact, almost the only source of potash. The formula, page 142, shows that a molecule or equivalent of feldspar contains one molecule of potash K2O, one of alumina Al2O3, and six of silica SiO2. This fact is taken into account in calculating the mixture or batch weight.
Base No. 5 (page 148), is as follows:
And this made up into a bisilicate glaze would be:
These items are extended in a horizontal line, a space being left on one side for the list of ingredients.