“I began to think that if I should discover how to make enamels I could make earthen vessels and other things very prettily, because God had gifted me with some knowledge of drawing.”—Palissy.
—Palissy.
It is in this department of potting, with its surprises, difficulties, and disappointments, its rare but exciting successes, that for most potters the greatest interest lies. To those of a scientific bent it is perhaps the summit of the craft, but the artist groping amidst formulas and methods may take heart. The finest work in pottery was not produced by scientists alone and does not depend altogether upon the quality of its paste, its unique colour, or strange lustre. The last word, the form, decoration, and craftsmanship, is with the artist.
It is beyond the scope of a book of this description to enter into a necessarily long and complicated account of the different processes concerned in the composition of glazes. It will be sufficient to indicate their leading characteristics plainly enough to enable the student to start experimenting. Nonecan afford to miss opportunities for experiment, just as surely as none can afford to be always experimenting. For a full description of materials and glazes and their manufacture such books as those of Drs. Shaw, Furnival, and Hainbach are recommended.
Putting aside salt glaze we find a countless number of both lead and leadless glazes. They range from the thin silicious coating of the ancients up to the rich alkaline glazes of the Persians and Chinese; from the raw galena of peasant pottery to the rich Majolicas and fine hard glazes of modern commerce. Salt glaze is obtained by the vaporizing of salt inside the kiln at a great heat. The sodium oxide so formed combines with the silicates in the clay to form a very thin coat of refractory glass, intimately connected with the body. Porcelain glazes, though not differing so much in composition from the ordinaryfineearthenware glazes, are extremely hard, being compounded of kaolin, felspar, and quartz, with possibly limestone and ground sherds. It has in common with the salt glaze the close union with the body, so that when fractured the line of demarcation between glaze and body is indeterminable.
With a few minor exceptions the following list comprises the ingredients of all colourless glazes:
These materials must be free from all trace of iron. They are pulverized and some are calcined or oxidized. Then they are mixed in varying quantities to form the glaze mass. This mass is easily fusible when lead or borax is present in large proportions, more infusible or harder the more silica it contains, and very refractory if alumina is present in any quantity. The silica forming the glassy part of the glaze is stiffened by the presence of alumina, which stops any tendency to run.
Lead is very largely used as a powerful flux at low temperatures but is unsuited to hard glazes. Borax and boracic acid are important constituents of leadless glazes. They are used to replace some of the silica, than which they are more fusible. Matt or non-reflective glazes are opaque and less vitreous than the glassy glazes. They do not flux or run.
All these minerals are finely ground before mixing. Then those insoluble are mixed andfritted; that is, fused in a crucible or fritting furnace to a greater or less degree, according to the hardness of the glaze. Iffused into a glass, the melted mass is poured into water to facilitate the next process, which is its reduction to a fine powder by re-grinding. Then the completing ingredients are added and the mass coloured by the addition of metallic oxides. Of these the chief are:
and the more precious metals, in various forms, as oxides, carbonates, sulphates, and nitrates soluble in the glaze at great heat.
These metals impart the many varied colours found in pottery. Zinc oxide is used to brighten a glaze or to stabilize colour. Tin oxide, which is insoluble at great heat but remains in suspension, gives opacity.
This is no more than a skeleton outline of the intricate processes often used in the fabrication of a glaze. The manifold minerals, metals, oxides, acids, and alkalies are used in a variety of ways by the modern chemical potter.
To all this seeming complication is added the question of pastes and bodies. There then arises the great problem of fitting one to the other. Salt glaze and porcelain excepted, the finished pot presents three stratas. Outside is the glaze, next the body, then inside the glaze again. If the coefficient of expansion of these three layers differs, in otherwords, if the glaze does not fit, the result iscrazing, that bugbear of the potter.
This crazing, which has been followed up and developed into their delightfulcrackleby the Chinese, may show itself at once or only after a lapse of months. It appears as a minute network of fine cracks over the entire surface of the pot. It is often not unsightly, but sooner or later it must cause devitrification. The glaze after a time assumes an evanescent iridescence followed by a dull smoky appearance; finally, perhaps not for many years, it decomposes and peels off.
With low-firing natural clays rich in silica and iron, the craze is not of much consequence. The body itself at a moderately high temperature becomes non-porous. With hard short bodies containing lime or chalk it may have quite disastrous consequences. Water placed inside will eventually percolate through leaving a network of grey lines all over the pot and completely spoiling its appearance.
It will be readily granted that, whether porous or non-porous, a craze is most undesirable on any piece of pottery that may be used for food or drink.
It is here that the commercial potter is such an admirable fellow. Many of the glazes on modern tablewares are perfect for their purposes. Sometimes only a little more fire is needed to stop the nuisance, but a bad craze usually needs more attention.The glaze requires stiffening, and the addition of ground flint or quartz, China stone or clay and felspar introduces alumina and silica and raises the fusing point. The substitution of borax for a portion of the silica can also be tried and will permit the use of slightly lower firing point.
If the glazes are bought ready mixed, the body must be altered instead. Refractory China clays should be replaced by more fusible clays or some reduction made in the amount of infusible materials. The addition of ground sherds or flint will have a contrary effect should the glaze peel or crack at the edges, as it may do on a very silicious body. In working with natural clays on a moderate scale it will be found best to mix “fat” or rich natural clays with those of a more porous or hard nature. A few graded mixtures submitted to a thorough trial should soon show when a sympathy has been established between the body and glaze.
The receipts given on pages183and 184 will make good colourless glazes without fritting if thoroughly ground in a mortar and passed through a sieve. Numbers 3 and 7, when calcined, will give much more even results and they can be coloured by the addition of the oxides named. But simple as it sounds, the washing, grinding, fritting, re-grinding, and sieving is a long and laborious process demanding machinery, and on that account is unsuited to schools or potters of moderatemeans. Glazes like Nos. 1 and 2 will do quite well for elementary work but unless the appliances are to hand the manufactured article will have to be relied on for more finished and ambitious work.
If, indeed, you are already in possession of a good receipt for a fine colour and glaze, one quite worth while, so much the better. Mix it and feel the joy of the Compleat Potter unafraid of spoiling his own good shapes with a faulty or unknown glaze.
Admittedly, to get anywhere in an original direction systematic research is essential. One must keep on experimenting, keep on hoping, and keep on taking notes; but at the start let us not be too impatient or independent if we wish to produce good pots.
There is often among young potters a false pride that prevents them using, and among old potters acknowledging the use of, the manufactured article. Why this should be is a little difficult to understand. A painter might far more reasonably be ashamed to use modern tube colours or a stained-glass craftsman as logically insist on making his own glass, as a potter in the twentieth century refuse to avail himself of the wonderful range of glazes that modern research has placed at his disposal. These resources should be used intelligently, not mechanically, or by the book—artistically, inventively, secretly, if you will, but they should be used—until the multitudinous experiments have borne fruit and repeated trialsconvince you that at last you possess some gem of research worth, as well it may be, the months of patient toil engendered in its production.
The various receipts are given on pages183and 184 without analysis of the composition of the paste or body to which they were applied. The first group have been used on common earthenware clays with complete satisfaction. They are to be considered as points of departure for future experiments in which they may be modified at will, and not regarded as a contribution to the science of glaze making.
In colouring it will be found that combinations of cobalt, iron, and copper oxides give an interesting range of simple blues or greens; iron and manganese browns; and so forth. The colour mass or stain is ground fine and lawned, and from about 2 to 7 per cent mixed with the colourless glaze mass, according to the depth of colour required. The ordinary under-glaze colours may be used to stain glazes, the percentage being fixed by small trials. For the rare colours—turquoise, crimson, or purple—a more complicated process is necessary and only perfected after many trials. The ingredients of these fine colours are naturally kept secret by their fortunate possessors.
It must be noted that a glaze suited to one body may peel or run off an unsuitable one. Then a colourant is affected differently by a lead oran alkaline base in the glaze. Again, copper and iron oxides may help to flux a glaze, whilst cobalt or nickel will exert a contrary effect. Cobalt, being a strong colourant, will need a sparing use, whereas a similar percentage of iron will merely tinge the glaze mass. And soad infinitum.
It is self-evident that any attempt to emulate the vast range of the modern ceramic chemist is doomed to failure. To a craftsman the fabrication of one fine individual glaze or lustre is an achievement of which he may be proud, and for which he will find abundant and varied uses. In this connection it is encouraging to the craftsman to learn from so high an authority as W. Burton, Esq., F.C.S., that it is impossible to obtain with purified oxides the fine tones got by the Orientals with impure materials. Further, that the simple glaze of the Persians—a mixture of clean white sand with soda or wood ash or potash—is still the best for under-glaze painting. Although tastes differ so widely, invariably it will be found that more and more heat will be the cry. Imperceptibly this leads to the desire for hard, cold, “fat” translucent glazes, neither matt nor glossy. And on the summit, far out of reach, stand the wonders of the Old Chinese.
Lustres
There are several kinds of lustres, but the true lustres possess a pearly iridescence in addition to their colour. The copper and silverlustresof the eighteenth-century Staffordshire potters were thin metallic films over the whole surface of the glaze. Gold or silver solutions were used. Only where the gold was fired on a white clay is there any iridescence, and then hardly so pronounced as to deserve the name of lustre. The bismuth and other lustres made by the modern potter are combinations of metallic oxides and resinates dissolved in ethereal oils. These are painted on the glaze, transparent or opaque, but having almost invariably a lead base, and then fired at a dull-red heat. The medium disappears, and the metal in a finely divided state is deposited on the surface of the glaze. This, however, gives a painted look very different from the lovely irradiance of the Persian Hispano-Mooresque or Italian work.
With these the lustres were fired in a reducing atmosphere, one supercharged with combustible gases, the metals decomposed and fixed to the semifluxed glaze. The manipulation was not infallible and was attended with much risk; but the successful pieces are unrivalled, and according to Piccolpasso “paid in gold.” De Morgan, who more nearly approached the works of the Italian masters than any othermodern potter, used a very similar medium and method with his fine lustres. In the last few years lustres have been brought to such perfection, in preparation, application, and firing, that accident is practically eliminated. Glorious colours and gorgeous effects are obtained. Yet it may be said without senseless adulation of the merely mediæval that nothing has been produced superior, or even akin in spirit, to the work sent out from Persia, Spain, or the botega of the inimitable Maestro Georgio of Gubbio.
Lustres may be bought ready to apply. They are then painted on the glazed pot, which is re-fired at a dull-red heat in the ordinary oxidizing atmosphere. Once the painted look has been contrasted with the lustrous appearance of thereducedeffects there is only one kind of lustre for the artist. Fortunately, perhaps, their preparation is not easy, and the correct method of reducing is a difficulty to be overcome by practical experiment alone. Hainbach gives many practical receipts for lustres that are not beyond the scope of a craftsman. The reducing atmosphere can be obtained in an open kiln by the introduction at the right moment of any combustible giving smoke free from all traces of sulphur.
In firing with a muffle kiln the introduction of coal-gas free from sulphur is a matter attended with some risk at the necessarily low temperaturesrequired by the lustres. It should be approached with caution, and each mixture will have a varied firing point, the correctness of which is established only by trials.
Lustres applied with skill and restraint enhance the most beautiful glaze, but in unskilled hands they inevitably vulgarize and cheapen. The fresh, unsophisticated renderings of the Persians or the Moors and the virility of the Italians should be studied, but not merely imitated before working in this medium.
PAINTING OUTFIT.Fig. 55
Decoration
“The world is still deceiv’d with ornament.”—Merchant of Venice.
—Merchant of Venice.
Decoration has been touched upon briefly in one or two of the preceding chapters. To attempt a description of the various kinds of decoration which it is possible to place on a pot, another book would be needed. Their name is legion. They range from the simple and entirely satisfactory work of primitive and peasant peoples to the wonderful enamel decorations of the Chinese. With such an enormous field and varied choice it is difficult to particularize and foolish to dogmatize. The hints below are intendedbut to stimulate interest in the at present unexplored fields that lie beyond the beaten track.
Any representative collection of ceramics will prove a veritable treasure house of suggestion to the student. All will be there. The difficulty is to choose, and choose aright. The bold brushwork of Cyprus foils the marvellousfamillesvert and rose of the Chinese, the faultless Wedgwood sets off the virile Toft. One sees how the Italians, with almost crude colours,—blue, green, red, yellow,—developed their wonderfully robust school of figure painters; then their fancifularabesquesare prolific of ideas. The Greek style—red and black and white—is a rich field waiting for the reaper. The peerless Persian pots, the plaques from Spain, the steins and stoves from Germany, the fresh Delft wares; these and many others crowd round for recognition and disconcert the choice.
But having come so far, let us not choose the horrific style that models most faithfully a cabbage, tops it with a lifelike snail as handle, and cunningly converts the whole into a vegetable dish!... (in S. K. M.). Nothing should be more distressing to the artist than to see great skill and craft thus misapplied. Yet how often does the search after false originality lead only to meretricious cleverness or vulgarity, which creeps in unseen during the too close struggle with the craft.
But our muttons need tending. Broadly speaking, all decoration falls under three heads: Glaze; Relief; Painting;—subdivided into many combinations of these three classes.
The application of glaze has already been described. A pot possessing a noble form and glaze is obviously in no need ofdecoration; no artist would attempt it. The Chinese and Japanese are safe guides here. Their rich glazes and fine forms are set off in the simplest and most effective manner. This is potting, pure and simple.
Under relief, we group all modelling,—raised or sunk, embossments, flutings, mouldings, feet, handles, or applied figures. At one extreme come the earliest attempts at decoration in slip or clay, highly developed in the Gallo- and Egypto-Roman and Romano-British wares. The matured slip must be applied fairly thick to the still moist pot and then dried slowly. Any work applied to dry shapes is liable to crack in drying or leave in firing. Probably the most effective use of slip is seen in the old tygs and dishes of Toft and others of his time.
The simple spotting and surfacing has been carried to perfection by the Martin Brothers, who have drawn largely upon the vegetable world for their inspiration. Roman Aretine ware shows finely executed reliefs of foliage and figures. The enrichment was probably worked on the original shape, a mouldwas then taken, and the vessel pressed. (See chapter on Casting.)
Wedgwood carried this method still further (too far, maybe) and used different coloured bodies. The reliefs, so finely modelled by Flaxman, were fired, and from them moulds of a very refractory clay were made, calledpitcher moulds. The reliefs were then pressed and affixed to the vase, and the whole touched up by a skilled craftsman. A naïve and unpretentious form of this decoration is seen in the stoneware and salt-glazed pottery of the eighteenth-century English potters and the jollyBellarminesof earlier times. Small dies were used in the Orion ware, the pattern being stamped into the clay. German stoneware and theGrés of Flandersshow sunk and relief patterns. Between the two extremes lies a rare choice of style.
This method of using patterns lends itself particularly to fine commercial work when used with the restraint seen in the best of the above-mentioned styles. To the craftsman it offers a welcome chance to enlarge his production, but he must be well equipped. It is easy to acquire the mere mechanism of commerce without its splendid technique. Finally, the further the relief is developed the less will be the appeal of form and the less the possibilities of glaze.
The next division is painting.
It is in this branch of ceramic decoration that thewidest choice lies. The scale ascends from the simple earthy colourants applied to the unglazed pot in the manner of the American Indian up to the splendid enamels of China and the sumptuous but sterile wonders of—shall we say—Sèvres or Worcester. Much of the modern eighteenth- and nineteenth-century work is such a technicaltour de forcethat one hesitates to criticise it. But careful scrutiny will often show that the artistic difficulties have been undermined rather than overcome. Thus the frank frontal attack of the Persians on their absorbent ground or of the potters of Delft on their unfired tin glaze is never attempted, and probably never can be attempted in the factory of to-day.
The modern method of painting in fat oils on a prepared ground induces in any but the most accomplished a cramped and finnicky style. The best and really most beautiful results are seen in the delicatevertuof the eighteenth century. Snuff boxes and ladies’ knick-knacks exhibit the loveliest miniatures in an impressible medium. How far it is desirable to decorate pots with such pictures depends on the sophistry of the craftsman. (For, ever since painters were pampered by princes each erstwhile honest craftsman must needs try to turn painter!)
The Chinese who laboured with infinite patience upon their pots still seemed to preserve a spiritlacking in the works of their western imitators, and their avoidance of realism saved them from the many pitfalls that yawned for the Occidental.
The manner in which the Persians and Dutch preserved their freshness has been noticed already, but the encountering and surmounting of similar difficulties is at the bottom of most successes. A few of the methods of painting pots are here set forth, with some odd variants.
The colourants described under Glazes are also used for painting. Very finely ground and prepared, they are mixed with a flux or other vehicle and applied in various ways under or over the glaze. Simple colours can be made from the metallic oxides. They should be finely ground in a mortar well mixed with a little of the glaze with which they are to be used. This will do for the simplest work. For more subtle colours rather involved processes are necessary. The range of manufactured colours, both over- and under-glaze, is wide enough to suit all tastes, and when working on a small scale are infinitely to be preferred on the score of economy and dependability.
A method of painting entirely suited to beginners is as follows: A simplepaletteis prepared with the colours ground upon a slab of glass. The medium employed is a solution of gum arabic and water, the colours being applied directly to the green shape with a brush. The difficulty of firing glaze on theraw clay deters any attempt at high finish, and the absorbent ground develops a desirable freedom and directness of touch. When painted, the pot is dipped or poured in a transparent glaze and fired. The gum prevents the colour shifting during the immersion, but does not prevent the glaze adhering. This method can be satisfactorily employed on biscuit. More finish can be obtained and a richer glaze used without risk. Much skill and practice will be required to produce good stuff, as each touch, although not apparent before, will stand out distinctly and often disagreeably after the fire. The gum must be used sparingly; any excess will cause peeling and prevent the adhesion of the glaze.
For a still higher finish the biscuit is sized with a solution of gum tragacanth. This is smoothly applied until the pot is non-absorbent. The design, if elaborate, should be drawn upon the pot with a fine graphite pencil or, better still, India ink and brush. A common pencil is likely to show after firing, but the ink disappears entirely. The colours are then well ground and laid in with fat oil of turpentine or lavender oil.
To prepare the first oil, half fill a cup with pure turps, stand it in a saucer, and spill a little over the sides of the cup. After standing a little the fat oil is deposited in the saucer and the clear turps left in the cup. Long, flexible brushes holding plenty ofcolour are used and the fat oil thinned if necessary with clear turps. The colour should flow easily from the brush, being neithertackynor too fluid, and constant retouching is to be avoided. Keep all free from dust. Heavy, greasy-looking masses should be scraped off and repainted, otherwise they will flake off.
When the painting is finished, the colour ishardened on; that is, the gum and medium are fired off in the kiln, a dull-red heat being sufficient. This does anything but harden on, however, and the pot must be handled very carefully or the colour will rub off. The glaze should now be gently sprayed on, and then the final fire is given.
Another way is to apply a very thin spray of glaze before hardening on, just sufficient to fix the colour. The pot may then be dipped or poured without risk. In each case the oily medium must be quite dry before the hardening on takes place. After the glost fire the decoration is fixed and unalterable. Where possible, a hard transparent glaze is best for fine work. A soft glaze will always run if slightly over-fired, and the result is the obliteration of all brushwork.
Over-glaze decoration is applied in a very similar manner. Turpentine, fat oil, and lavender oil are used: the turps to run the colour, the fat oil to stiffen, and the oil of lavender to retard the drying.The colour must be applied evenly and thinly, thick patches being likely to peel or crack. On hard glazes this process lends itself to elaborate effects. The hard and fast colours, the blues and greens, may be fired first, the delicate pinks and greys last. The whole effect may then be enriched with low-firing lustres. These, when bought in bottles, are ready to use and are applied directly with a fine brush, then fired at a dull-red heat. The pot should then be quite finished; quite frequently it is.
Pâte sur pâteor painting in relief colours is another process that has many attractive features. The colours have a clay carrier and are applied with a gum medium. Painted boldly with a certain amount of relief, this gives a rich enamel effect very suitable to simple figure decoration.
The full equipment of the painter will be as follows:
Before risking decent shapes in the fire, trials,—onbiscuit for under-glaze, on glaze for over-glaze,—should be made repeatedly. Graduated strips and stripes tartan fashion are the most useful and easily tabulated. To lay perfectly flat grounds some skill and practice are necessary. One method is to paint in the ornament or rather the space it will cover with thick molasses or black treacle. This is allowed to harden and the background colour applied with a soft dabber. It must be ground fine with fat oil and applied very evenly. Then the tile or vase is soaked in water, which causes the treacle to peel off. The oil is allowed to dry and the piece fired. This fixes the background, and the decoration itself is next applied.
Pierced work if skilfully done is most attractive. The pattern may be incised on the “original,” which is moulded, the design then showing in relief. This again shows as a slightly engraved pattern on each cast form or shape. Then with the aid of a fine-pointed knife or plaster tool the pattern is cut out and the edges are softened to take away any metallic look. The Chinese and Persians are said to have used rice seeds in some of their translucent effects. The seeds were embedded in the moist clay to form a delicate tracery. When fired, the grains disappeared, leaving holes which were completely filled with glaze.
The decorative possibilities of simple incised linesand plain slip additions have been hinted at already. The slip may be coloured red or brown with iron and manganese oxides or applied white to a coloured body. Sharply incised lines may be filled in with colour stiffened by the addition of a littlehardclear glaze or China clay. Patterns may be dug out or stamped in and filled up with different coloured clays and the whole glazed with a coloured transparent glaze. Scraffito work is effective and not difficult. The green pot, tile, or dish is sprayed evenly with a different coloured slip, usually red on white. The piece should not be quite dry and the coefficient of expansion between the two clays as near alike as possible. The decoration is then sketched in and the background or the ornament itself gently scratched away to show the ground beneath. It is then fired, glazed, and fired again. All these processes have their uses and abuses, but they do not lend themselves readily to elaboration or realism.
STATUETTE FOR A THREE-PIECE MOULD.Fig. 56
Figurines
“But if you carve in the marble what will break with a touch, or mould in the metal what a stain of rust or verdigris will spoil, it is your fault not mine.”—Ruskin.
—Ruskin.
The making of small figures is an important department of ceramics scarcely mentioned so far. It is one offering exceptional opportunities to the advanced craftsman. In this branch of potting, even more than any other, the possibilities and limitations of the clay and glaze need close study if best results are to be obtained. The archaic Sung and Tang figures and the well-known Tanagras are far better guides to the beginner than the wonderful Dresden porcelain or thebisquegroups of Sèvres. The Chinese and Japanese in their glazed figures show remarkable appreciation and utilization of the plastic and liquid qualities of their medium. Splendid and sound work, too, has been turned out in recent years in Germany and Austria, whilst the Copenhagen porcelain is world famous.
To start with, the simplest decorative figures might be attempted. Many of the little deities ofancient Egypt offer rich suggestions for two- or three-piece moulds. Japanese Netsuke and Scandinavian bone carvings are other stimulating, if more remote, fields. Next, a more ambitious but still uncomplicated figure could be moulded directly from the clay. As the difficulties of moulding increase, the original clay may be first fired or a good plaster cast made. In firing the figure a very slow fire must be used, and the modelling must be done carefully, as free from holes as may be, and without an armature. Air holes are apt to blow, and additions of soft clay to the model when hard are likely to crack off in firing.
SIDE VIEW, FIGURINE.Fig. 57
With a plasteroriginalsome retouching is possiblebefore the final piece-mould is made. When modelling the head and face, the modifying effects of the glaze used must be realized, so that such detail as may be depicted shall have its full value in the finished figure. Too much realism in draperies with consequent under-cutting is to be avoided, and the inclination of all but the high-temperature glazes to leave prominent parts and pool in hollows must be heeded. Sharp edges are always bad, and projections that are liable to crack in the fire or break at a touch are a fruitful source of loss, and are, at the best, doubtful craft. It is quite possible to produce delightful figures glazed with low-firing glazes, and where a wide range of colour is desired, they are the only glazes available. But for delicate modelling, where colour is a secondary consideration and where refinements may be obscured by too much gloss, the grand feu porcelain or salt glaze are the best and only alternatives.
But each man to his taste. We will start with a simpletwo-piecemould for pressing. Small objects, not necessarily figures, may be modelled in the round, being designed therefore without under-cut topullin two halves. They should be highly finished and then biscuited. The fired original is then shellacked or oiled and carefully bedded in clay up to the halfway line. If the figure be first dusted with French chalk, it will leave the clay without trouble.Little walls being built, the first half is then cast. When set, the biscuit figure is removed, the sides of the mould trimmed, the joggles cut, and the figure fitted back. The sides are carefully clay washed or oiled and the second half of mould cast. When set, the two halves are gently pried apart and a groove hollowed out all round the inner edge of the mould. (Figs. 58 and 59.) This groove is for the reception of any surplus clay that would otherwise squeeze between the two parts of the mould and prevent their perfect adjustment. To make apress, each half of the mould is carefully filled with clay, well pressed in. Then they are applied and firmly squeezed together, until the two halves fit exactly. The press is then removed and trimmed up.
FIGURINE FOR TWO-PIECE MOULD WITH BACKPIECE IN POSITION.Fig. 58
The second essay might follow the lines of the statuette here illustrated for the three-piece mould.A decorative treatment, giving stiff lines and a simple silhouette, is chosen. The hands are concealed, and the face, the only flesh showing, clearly cut out by the costume. The section shows the comparative depth of the folds in the drapery. Three pieces only were used for the mould, indicated by the illustration. (Fig. 63.)
In moulding from plaster or biscuit the model must be absolutely non-absorbent and should be carefully treated with shellac, beeswax dissolved in turpentine, or parting. Beeswax is best for fine work and should be applied very thinly and repeatedly. Clay originals need no preliminary treatment, if the clay is still plastic.
SECTION OF TWO-PIECE MOULD FOR PRESSING. SHEWING GROOVE FOR RECEPTION OF SURPLUS CLAY.Fig. 59
The divisions of the mould being decided upon, plastic clay is rolled out thin, cut into strips, and built round the section, as shown in the illustrations. (Figs. 60 and 61.) The exposed figure within the clay walls is then very slightly filmed with olive oil. The plaster is then mixed and thrown on or poured. The walls should stand out at right angles to the circumference of the figure or so nearly as the exigencies of the figure permit. They should bebuttressed where needing support, and be deep enough to give a good thickness to the mould. When the plaster sets, they may be removed, and when quite hard, the plaster itself detached. This comes away quite readily from the clay, but is apt to hold on plaster or biscuit. A little water dropped from a clean sponge onto the cleaving line will often release the two parts.
CLAY WALLS FROM FRONT—Saint George Statuette.Fig. 60
CLAY WALLS BUTTRESSED AT BACK.Fig. 61
The model iscleaned up and the sides of the first section trimmed, slight joggles made where they will not bind, and the edges carefully shellacked or claywashed. (Fig. 62.) Model and section are then fitted together and the next section made in a similar manner, except that only one wall of clay will be built. The second section is treated in the same way, and for the last piece the clay wall is unnecessary, the plaster being poured directly in between the two other sections. Where the plaster has to be sprinkled on, or there is any danger from splashes, the exposedparts of the model should be protected with soft paper.
FIRST PIECE OF MOULD.Fig. 62
The last piece being set, the original is removed, the mould assembled, trimmed, or fettled, tied up, and set to dry. The casting, or pressing if it be large enough, is proceeded with as before described, the slip being poured in at the base. When removed from the mould, the open base of the cast may be closed with a thin slab of clay slip poured on to a plaster bat and allowed to set for that purpose. When tough, the figure should be touchedup with skill and reticence. Finally, a little hole is made in the closed base and another as inconspicuously as may be in the back of the head, to prevent blowing in the fire.
SECTION OF A PIECE MOULD & RETAINING CASE WITH FLAT TOP TO FACILITATE PRESSING.Fig. 63
With more complex figures many more pieces will be needed for the mould. They are made in the same way, but are carefully trimmed and then encased in an outer frame or jacket of plaster. (Fig. 63.) Large figures should be pressed; the head first, the differentsections of the mould being fitted into the containing case as the work progresses. More retouching is needed with pressed figures, but the time spent is well spent, for they possess a substance, and when retouched with art, a character, that is lacking in the more fragile cast.
SECTION SHEWING DEPTH OF FOLDS IN DRAPERY.Fig. 64
FUELING KILN.Fig. 65—Early Greek Kiln.
Kilns
“By many long, laborious, and chargeable experiments he hath found out.”—Extract from an old potter’s patent.
—Extract from an old potter’s patent.
What must be the first representation of a kill, or kiln, is found at Beni Hassan. It appears to be square in form, and the potter is shown feeding the fire at the base. In the same illustration he is depicted unpacking or drawing the ware from the top. The cut from the Greek Hydra gives a verysimilar kiln, but a vessel in the museum of Berlin shows one with a beehive shape.
The kilns left scattered about Europe by the Romans were usually of this domed kind, circular in plan, with one fire hole. The floor of the kiln was of pierced slabs, and the flames issuing thence enveloped the ware piled within and escaped through a vent in the top. The packing and firing is described inCeramic Art in Great Britain, by L. Jewitt, F.S.A. It fully explains the trepidation of the old potters, who, before each firing, were wont to consult the moon and stars and evoke the aid of the gods. This is happily set forth in Cowper’s translation of one of Homer’s epigrams, wherein he expresses the pious hope that if the false potter “stoops to peep into his furnace, may the fire flash in his face and scorch it”; a risk often faced by potters, false or true!
The smothering, or reducing, as then practised, was similar to thelustringmethods used in Italy in the sixteenth century, or in the manufacture of thebluebricks to-day. The Japanese and Chinese built small kilns in tiers on the side of a hill. Starting with the lowest, the waste heat was utilized to warm up the kiln above, thus saving time and fuel. The Chinese used heavy saggars, and specimens of these with portions of melted pots still adhering to them attest the enormous heats to which they frequently attained.
Modern kilns subdivide roughly into biscuit, glost, and enamel. The first is used for firing the green or clay shapes, the second for the hard fire of the glazed ware, and the last-named for fixing on the added decoration. Sometimes a kiln is used for the double function of biscuiting and glazing.
Of modern kilns the one still most widely used approximates to the bottle-shaped, simple, up-draught kiln. It contains one or two chambers with hatch for entry, flue or chimney, and anything from three to nine fire holes. The section of such a kiln is here shown and represents a fair average up-draught kiln (Fig. 66), variants of which type are working in most pottery districts to-day. In these kilns the flames rush in at the fire holes, play on the built-upbungsof saggars, and escape through the top vent. In a two chamber kiln, as sometimes used for porcelain, the glaze is put in the lower chamber to receive the hottest fire, the biscuit in the upper getting a gentle fire. Where the fire enters directly into the kiln in any large volume,bagsor small chimneys are built up inside the mouths to save the saggars from the worst of the fire. Of late the single-chamber, down-draught kiln has come into favour, as it is easily packed and economical of heat. Bags of firebrick protect the saggars from the roughest fire and direct the flames to the crown of the chamber, from which point they descend to pass out through flues in thefloor of the kiln. (Fig. 67.) Biscuit ovens are often of this type, either domed or flat arched.
UP-DRAUGHT KILN.Fig. 66
DOWN-DRAUGHT KILN.Fig. 67
The most recent innovations are gas and oil kilns. They require comparatively little manual labour in the firing, are easily regulated, and the waste heat is frequently used for secondary purposes. Their freedom from smoke and their economy of labour and money must eventually render the other types obsolete.
These large kilns are strongly banded with iron supports designed to prevent too much loosening of the walls when expanded by the great heat. A very important point is the draining of their site,as large kilns tend to attract moisture, and the presence of steam in a kiln is productive of much damage.