Pottery, for Artists Craftsmen & Teachers Part 5

--Sixteenth century memorandum.

Tiles may be made of various kinds and sizes, but in every case they show an inclination to buckle in drying and firing. The larger the tile the stronger is this tendency to warp. The clay must not be so rich as that which is used for throwing and should be tempered to counteract the tendency to curl.

A tile box as shown in Fig. 39, or a variant of it, will be required for pressing tiles by hand; for plain tiles 5/8" deep, for others 1-1/4" deep, the size being calculated to allow for shrinking. The sides hinge and the thumb screws keep it steady on the bench during work. For rough tiles, two strips nailed to the table will serve, the clay being rolled out between and cut in lengths as required.

For plain tiles the wedged and tempered clay is batted out into a slab a full 3/4" thick. The mould is dusted with French chalk, flint, or very finely sifted clay dust, to prevent sticking, and into it is pressed a piece cut to fit easily in the tile box, from the slab. This is firmly pressed into the box, considerable pressure being used. The surplus is sc.r.a.ped off and the top trued with an iron straight-edge. The knife can be run round the sides, then with the frame reversed a smart tap on the back will release the tile.

[Ill.u.s.tration: FIG. 39--TILE FRAME--6-1/2" x 13".]

Let the tiles toughen and then pile in stacks with flat pieces of clay or old tile between each corner and a true biscuit tile at bottom and the top. They can be piled one on the other with sand between or stacked like bricks with alternate holes for the air to circulate. This r.e.t.a.r.ds the drying, but in any case they must be dried slowly. With plain glazed tiles a little coa.r.s.e dust sprinkled over the surface before the tile is removed from the box, and well pressed in, will give a slight interest to the surface and take away any mechanical look. If required for painting, the clay must be very finely sieved and the surface will need careful finis.h.i.+ng by hand when dry. With coa.r.s.e clay, a fine surface can be imparted with a flexible broad palette knife.

For raised outline tiles a frame 1-1/4" deep is required. This allows a plaster bat 5/8" thick to be placed at the bottom. The best way, perhaps, is to oil the frame and cast the bat in it, removing it when set and sandpapering the upper surface flat and true. The design for the tile drawn the exact size on paper is now traced on this surface. It is far better to sketch it directly onto the slab, but this demands some proficiency if the surface is to be preserved. The design is then incised with a firm sharp point, clay squeezes being taken from time to time to show the progress of the work. The plaster should be wetted to insure easy working. At the finish the design should stand out in a fairly strong and deep line--square--not round or angular in section. (Fig. 40.) A chisel-pointed hard pencil will be found best for finis.h.i.+ng. This gives a clear-cut line, not too round. The bat, sponged clean and porous, is then placed in the frame and the tile pressed as before.

[Ill.u.s.tration: FIG. 40--A: POINT FOR FIRST OUTLINE. B: DO. FOR FINAL INCISED LINE. C: SECTION OF INCORRECT CLOISSONS. D: CORRECT.]

Raised outline tiles can be even more satisfactorily made by means of outlining slip squeezed from a tube or tracer in the same manner that inscriptions are made on sugared cakes, but this requires much practice to obtain good results. When glazing, the coloured glazes are applied to the different compartments with a brush. As the glaze fuses to about one third of its bulk when dry, it should be applied very liberally.

It will be found that large or elaborate designs are to be avoided, as in this process they tend to become mechanical and look thin. The old Spanish and Moorish tiles in this style with jewel-like bits of colour are excellent guides and might be studied with advantage.

[Ill.u.s.tration: FIG. 41--SLIP TRACER.]

The process of making encaustic tiles is a little more complicated. Within the frame is placed a well-lathered or soaped plaster bat (or tile) high enough to allow only a thin layer of clay 1/8" thick being run out on top.

On this when firm the design is traced or pounced. Then with a thin sharp blade it is cut down vertically to the plaster bat, and the clay removed until the whole design shows in white plaster beneath (see ill.u.s.tration 42). The face of the clay left must be preserved carefully, as it forms the surface of the subsequent press.

The bat with clay is now placed on the bottom of the frame to allow a cast 5/8" thick to be made. The plaster and the sides of the frame are slightly oiled and the plaster mixed and poured in. A soft hair brush will be useful to dislodge the air bubbles that are certain to hide in some of the many odd corners. When nearly set, the surface of the plaster can be sc.r.a.ped flat, and when set taken out of the frame and detached. The clay is picked out and the whole surface of the design cleaned and trimmed so that it will not hold or bind in pressing. This in turn is placed in the frame and a careful press taken. The result is a sunk design into which a different coloured clay is pressed, the tile being first allowed to toughen. The surface is lightly sc.r.a.ped flat and the tile slowly dried.

When hard, the face is sc.r.a.ped again with a steel straight-edge, sandpapered, and dusted, when the design appears in two colours. (Fig.

43.)

[Ill.u.s.tration: FIG. 42--CLAY LAYER CUT OUT ON BAT & PLASTER DIE.]

The most effective clays are fairly siliceous reds, buffs, browns, and greys. When tempered with flint or quartz sand to a uniform degree, they offer a splendid opportunity for counterchange pattern. If a soft clay that contracts considerably is inlaid in a refractory clay, cracks will appear round the edges of the inlay. Thus it is found best to have the body of the tile made of the clay that contracts most.

[Ill.u.s.tration: FIG. 43--STRIKING OFF FACE OF TILE IN FRAME--SECTION ON A-B.]

Where only a single tile is required a more direct method is possible. The tile is pressed and allowed to toughen slightly, the design being transferred as before. It is then cut round with a sharp knife and the waste removed with a wire tool. A certain facility of handling is required, for great care must be taken to preserve the edges and angles.

This method is, however, productive of much fresh and vigorous work.

Encaustic tiles must necessarily be simple and bold in character, for anything complicated invites confusion; the best possible guides are the encaustic tiles of mediaeval times, especially the simple and spirited English and German Gothic.

The most satisfactory way to make modelled tiles or panels is to run out upon a stout board, cross battened to prevent warping, a flat slab of clay of the required thickness. Sketch in the design with a point and model straight away onto the clay. Care must be taken, if the panel is to be fired, to see that all the added work adheres firmly to the background.

Where several presses are to be made, the edges of the modelled slab should be carefully trimmed with a bevel, the board oiled, and the mould made directly after the modelling is finished. The mould may be worked on in moderation. Lettering is much more easily incised in the mould than raised in the clay. For tiles needing much sharpness of detail almost the whole can be carved in the plaster. Unless done with great sympathy, however, this leads to a certain harshness and angularity that should be foreign to clay. Where a moulded frame for a panel is required, a _strickle_, or profile, is cut in zinc. For short use one made from a thin slab of plaster will serve. The strickle is keyed to a straight-edge and dragged over the clay until the correct moulding emerges. This is then cut into lengths and very carefully dried.

The tendency of all transparent gla.s.sy glazes to pool in hollows and run off at high points must be borne in mind. With thick matt glazes any delicacy of detail is apt to be lost labour. These problems should be faced before the design is made, as in this process there is a certain quality of surface required by the glaze. On the other hand, in endeavouring to make a good surface for the glaze to enhance, it is easy to slip into the over-round and slimy treatment that characterizes so much modelled pottery.

CHAPTER IX

DRYING: FINIs.h.i.+NG

"There nis no workeman whosoever he be That can werke bothe welle and hastile."

--"Merchants Tale."

Drying out is quite an important part of pot making. For this a drying cupboard is a necessity. It is easily erected, if the front and sides of wood be backed against a wall. Across the bottom, which should be open, run a row of gas jets protected above by perforated zinc or iron. At the top, which is boarded in, place a small sliding panel to insure a draught.

With side brackets and removable shelves it should answer all purposes. A cupboard may be built over a radiator, but here the heat is not so easily regulated.

A thermometer inside the cupboard will be an advantage, for a wet pot straight from the wheel will warp in a warmth that would be quite suited to tough shapes. The green or damp wares should be put on the top shelves and brought nearer the heat as they dry. Large shapes put into the cupboard to dry quickly are very liable to crack across the base. Any flush of heat upon them through any aperture in the shelves will cause them to dry streakily. Turning then becomes difficult or impossible.

Bowls, if not too fragile, may with care be piled one within the other.

This helps to retain their shape. Tiles are best stacked in piles dusted with flint or with a piece of clay at each corner between them. Tiles should never be placed in the cupboard until quite dry and straight. Flat platters or dishes require very careful drying to prevent buckling and should be reversed on a piece of sanded gla.s.s. When shapes are dried in the open air, they often get hard at the rim before the bottom stiffens.

They need reversing to counteract this tendency.

To r.e.t.a.r.d drying, which may often be necessary, a damp-box is needed. A large box, zinc-lined and fitted with plaster slabs, is an excellent device. The plaster must be kept moist with water. A well-tarred box with a close-fitting lid is more easily constructed and will serve most purposes. All work to be _stuck up_ or modelled on should be kept in the damp-box until quite finished and then dried very gradually.

In all kinds of sticking up the body and the addition should be of the same consistency. Re-wetting is dangerous but may be resorted to in moderation with stout thrown shapes. Ornament added when the shape is nearly dry is very likely to leave in the biscuiting, although apparently quite firm in the green state. Cast shapes dry very rapidly and should be finished before they become white dry. With practice handles, masks, and the like can be affixed in the dry state with slip, but it demands its careful and sparing use. Cracks or holes in dried shapes can with great care be filled, a stiff wedge of clay being firmly pressed in and welded to the slightly moistened sides of the crack. The plaster tools (Fig. 44) will be found very handy for working on the dry clay. With skill and patience much repairing may be done on unfired shapes, but it is a waste of time to attempt it unless the beauty of the piece warrants it. It is far better if the piece be faulty to throw it back into the bin at this stage. Once fired, it is likely to remain an irremediable eyesore.

[Ill.u.s.tration: FIG. 44--PLASTER TOOLS.]

One or two other points bearing on finish have been mentioned before in previous chapters, but these last touches are so important that they will bear some reiteration.

The finality burned in by the biscuiting should induce a careful and sound completion of each object; yet paradoxical as it may seem, the less finis.h.i.+ng, the better for the piece. It is no part of a craftsman's work to go finnicking with file and sandpaper; too frequently nothing remains of what might have been a vigorous shape but a meticulous finish. The best j.a.panese work was superb in this respect and despite the many quaint and surprising shapes into which they fas.h.i.+oned the clay, it very rarely seems to lose its plastic character, it never a.s.sumes forms more suited to metal, wood, or stone. Again the character that comes with correct treatment is never smothered. Often the ribs or ridges made by the fingers or the tool in forming the shape are frankly left to contribute their quota to the general effect. The lips are rounded with scrupulous care and angles removed without a suggestion of weakness.

Where large utensils, ewers and the like, are in question, mediaeval pottery is rich in suggestion for handles, spouts, and such added forms.

It is only when such additions are affixed that one realizes the nicety of adjustment required between the size, shape, and situation of the handle or spout and the vessel to which it is attached. It is here that an appreciation and an intelligent use of historic ornament is necessary.

CHAPTER X

FIRING BISCUIT

"The Pope, the Cardinals, and the Princes of the World are astonished that such excellent and n.o.ble works can be made out of the earth."

--EXIMENUS. Fifteenth century.

When sufficient green shapes have been acc.u.mulated and are white dry, the next stage will be _biscuiting_. This process is the firing of the clay to a primrose or a white heat according to its fusibility. This permanently expels the water that is always present, even when dry, and converts the friable clay into a hard unalterable body. This may vary in colour from the white of kaolin to ivory, grey, buff, red, or brown, according to the composition of the clay; it may be vitreous or porous; soft like common flower pots or so hard that it will spark when struck with steel.

The fire is the ultimate test of the pot and of the potter. It is indispensable to both. With but a small kiln the craftsman will begin to appreciate many things that can be learned only at the _fire hole_.

Without a kiln he will not commence to be a potter.

[Ill.u.s.tration: FIG. 45--GAS KILN. SECTION SHOWING CLOSE PACKED BISCUIT.]