Pottery, for Artists Craftsmen & Teachers Part 9

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.

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 the _bisque_ groups of Sevres. The Chinese and j.a.panese 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 of ancient Egypt offer rich suggestions for two- or three-piece moulds. j.a.panese 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.

[Ill.u.s.tration: FIG. 57--SIDE VIEW, FIGURINE.]

With a plaster _original_ some retouching is possible before 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 simple _two-piece_ mould for pressing. Small objects, not necessarily figures, may be modelled in the round, being designed therefore without under-cut to _pull_ in two halves. They should be highly finished and then biscuited. The fired original is then sh.e.l.lacked 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 a _press_, 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.

[Ill.u.s.tration: FIG. 58--FIGURINE FOR TWO-PIECE MOULD WITH BACKPIECE IN POSITION.]

The second essay might follow the lines of the statuette here ill.u.s.trated 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 ill.u.s.tration. (Fig. 63.)

In moulding from plaster or biscuit the model must be absolutely non-absorbent and should be carefully treated with sh.e.l.lac, 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.

[Ill.u.s.tration: FIG. 59--SECTION OF TWO-PIECE MOULD FOR PRESSING. SHEWING GROOVE FOR RECEPTION OF SURPLUS CLAY.]

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 ill.u.s.trations. (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 circ.u.mference of the figure or so nearly as the exigencies of the figure permit. They should be b.u.t.tressed 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.

[Ill.u.s.tration: FIG. 60--CLAY WALLS FROM FRONT--Saint George Statuette.]

[Ill.u.s.tration: FIG. 61--CLAY WALLS b.u.t.tRESSED AT BACK.]

The model is cleaned up and the sides of the first section trimmed, slight joggles made where they will not bind, and the edges carefully sh.e.l.lacked 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 exposed parts of the model should be protected with soft paper.

[Ill.u.s.tration: FIG. 62--FIRST PIECE OF MOULD.]

The last piece being set, the original is removed, the mould a.s.sembled, 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 touched up 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.

[Ill.u.s.tration: FIG. 63--SECTION OF A PIECE MOULD & RETAINING CASE WITH FLAT TOP TO FACILITATE PRESSING.]

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 different sections 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.

[Ill.u.s.tration: FIG. 64--SECTION SHEWING DEPTH OF FOLDS IN DRAPERY.]

[Ill.u.s.tration: FIG. 65--Early Greek Kiln.]

CHAPTER XV

KILNS

"By many long, laborious, and chargeable experiments he hath found out."

--Extract from an old potter's patent.

What must be the first representation of a kill, or kiln, is found at Beni Ha.s.san. It appears to be square in form, and the potter is shown feeding the fire at the base. In the same ill.u.s.tration he is depicted unpacking or drawing the ware from the top. The cut from the Greek Hydra gives a very similar 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 in _Ceramic 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 G.o.ds. 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 the _l.u.s.tring_ methods used in Italy in the sixteenth century, or in the manufacture of the _blue_ bricks to-day. The j.a.panese 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-up _bungs_ of 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, _bags_ or 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 pa.s.s out through flues in the floor of the kiln. (Fig. 67.) Biscuit ovens are often of this type, either domed or flat arched.

[Ill.u.s.tration: FIG. 66--UP-DRAUGHT KILN.]

[Ill.u.s.tration: FIG. 67--DOWN-DRAUGHT KILN.]

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.

[Ill.u.s.tration: FIG. 68--ENAMEL OR m.u.f.fLE KILN.]

Enamel kilns are used for the final processes where the glazed pot is painted with over-glaze or enamel colours. They are of no great size and are made of fire-clay slabs or even iron plates when the enamel is soft.

The flames play all round the m.u.f.fle or fire-clay box during the firing, but no flame or fume is allowed access to the inside. (Fig. 68.)

In packing a kiln with biscuit or glaze much care, thought, and expedition have to be exercised. An experienced setter is essential in a factory if the pots are to have every chance in the fire, for all kilns vary and have their hot and _cool_ corners. First, the floor is well bedded with quartz sand or flint that will not vitrify but will provide a good setting for the bottom saggars. These saggars are fire-clay _boxes_, round or oval, rarely square, and without lids, in which the pots are placed. Piled one above another they form the _bungs_, the bottom of one supplying the top of that beneath. These bungs are built at intervals that permit the flames to penetrate between them and give a good even fire all over the chamber.

In actual practice some parts of a kiln are hotter than others, and it is here that a good setter shows his capabilities, setting the thin wares in the softest places and putting the heavier biscuit or hard glaze in the hottest corners. With biscuit the setting is not difficult except where delicate or friable ware may need very careful bedding and propping. With clean saggars the biscuit may touch the sides, and a competent man will pile an enormous amount of biscuit into a kiln without risk. In the glost kiln the ware requires gentle handling and must touch nothing but the spur or support. The saggars are usually given a saggar wash of lead and stone to prevent them absorbing glaze from the wares, for a glazed pot placed too near a raw saggar is very likely to come out with a thin or dry patch.

When the pot is firmly placed on its stilt, a roll of _pugging_ is placed round the rim of the saggar; this provides a firm bed for the next above it and also stops the entry of dust and flame. This pugging is made from clay or marl mixed with ground sherds, sieved gravel, or some non-vitreous dust to prevent it sticking to the saggars. The plugging is made malleable with a little water and rolled out by hand or pressed through a die. It will readily be seen that a carelessly built bung of any height may slip in the stress of firing, and its fall would most likely involve others, whilst any slight movement may be sufficient to cause a vase to topple off its stilt. In a down-draught kiln the bungs over any vent must be raised on fire tiles to permit the escape of the flames. When all the bungs are filled up and piled in position, the trials and cones placed, the hatch is bricked up. Spy holes are left where necessary, and the whole well clammed to prevent the loss of heat during firing. When fired, the hatch may be very gradually loosened to accelerate the cooling.

[Ill.u.s.tration: FIG. 69--DOWN-DRAUGHT KILN.]

The fireman's job is one of the most arduous and important of all the prolonged processes of potting. Coming as it does at the end, it may make or mar kilns of great value, and it requires more than ordinary judgement and nerve. The chief troubles arise from bad or irregular draught or impure fuel. They express themselves in the form of clinkered holes, excessive smoke, and irregularly fired or sulphured ware. The term _sulphured_ is applied to pots that come out gloomy or dulled and is said to be equally due to a reducing fire or an oxidizing one. In the former an insufficiency of air causes excess of carbon in the kiln and the absorption of oxygen from the glaze. In the latter an excess of air (oxygen) allows sulphur vapour, if present, to attach itself to the glaze.

The fire bars, fire holes, and flues must be kept clear and the fuel carefully selected if these things are to be avoided. The aim, as previously stated, is a gradually increasing fire, sharper towards the finish. For this purpose some potters finish off with wood which gives a long flame free from sulphur and clears the glaze. Even when sulphured, a clear flame at the finish will remove many ill effects. The baiting should be fairly heavy at the start, lighter and more frequent towards the finish, when smoke in any quant.i.ty should be avoided.

For temperature gauges, the cones previously described are used and should be placed in an average place, screened as much as possible from draught or flame. Small sight pots and glaze rings placed near the spies can be hooked out and examined and are valuable aids, but their exposed position and the corrosive action of the flames must be taken into account.

Pyrometers are also used, but with all these aids the experienced fireman pays due regard to sight and colour.

For a craftsman, the kilns that have been described are unsuitable on account of their size, if they are not altogether beyond his means. But a kiln of some sort is indispensable to a potter. The craftsman is nothing if not inventive. Small trials can be fired in crucibles in an open fire or on a gas ring. I have heard of some preliminary success with a gas cooker, discounted later by a frontal attack from the cook. Considerable knowledge can be gained from small, easily constructed, experimental kilns.