Читать книгу A Manual of Mending and Repairing; With Diagrams - Charles Godfrey Leland - Страница 5

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Fictile or Ceramic ware embraces, roughly speaking, all that is made of clay, or mineral bases or materials, and which is subsequently baked to give it hardness. The better the material and the more intense the heat, or the greater the number of bakings to which most kinds are subjected, the harder and more lasting will they be. The old china ware which preceded porcelain, a great many specimens of old Roman vessels, and, for a more modern example, old Italian majolica and Hungarian wine-pitchers, made all within a century, are as hard as stone. They chip a great deal before they break, just as agate might do.

Terra-cotta is simply earth or clay “baked.” In most of the examples known as terra-cotta, earth predominates. Pure fine clay well fired is superior to what is generally called terra-cotta. Neither can we really class with it articles made of superior Portland cement, of which, as I have said, I have seen many made at Budapest which were like the finest hard slate.

Many writers confuse majolica with faïence; others regard the latter as what we should call crockery, or such ware as ranges between glazed terra-cotta and porcelain.

Majolica consists generally of terra-cotta covered with a glaze. A glaze is a fusible substance, we may say a kind of glass, mixed with colouring matter, which is at the same time a protection and an ornament. Enamel is glass in fine powder melted, used generally on metal or by itself. The base of the paint is a substance fusible by heat which is mixed with colours also fusible. Therefore when the painting is submitted to heat it melts, adheres, and is permanent. Glazing, enamelling, and china painting are essentially the same.

Terra-cotta is not difficult to mend. I can best illustrate this by an example. A friend once gave me a terra-cotta vase from the Pyramid of Cholula, in Mexico. These are supposed to be of very great antiquity. This contained a fragment of pottery, probably a sacred relic of ruder style, and I suppose of far earlier times. The vase, however, had been broken to fragments, and the owner was about to throw it away as worthless. I begged it of him. Firstly, I put the principal pieces together, using, to make them adhere, glue with nitric acid. For finer work I should have used Turkish cement or the best gum-mastic dissolved in spirit or fish glue. Piece by piece with care I reconstructed the whole.

There was wanting, however, one piece about three inches square. I pasted with great care a piece of paper inside the vase for a back, and then poured on it plaster of Paris liquefied with water. To make this set hard, the plaster or gesso should be made with burnt alum-water and dissolved gum-arabic. This exactly supplied the missing piece.

When it was finished, I filled in all the broken edges and other cavities with the plaster-paste, which set even harder than the terra-cotta. The outer colour of the vase was of reddish rusty black. I painted the whole over with a corresponding colour; that is to say, I rubbed it in by thumb, which is very different from mere painting. By cementing and rubbing I so restored the whole that the repair was hardly perceptible. This process is carried to great perfection in Italy with broken Etruscan ware.

I may here remark as regards rubbing in oil or water colours, that it is little known or practised, but it is of great value in restoration when we wish to produce certain curious antique-looking effects. I once knew in Rome an artist who had bought for a trifle an old carved baule or chest. By rubbing in with care on it Naples yellow and brown shades, and subsequent friction, he had made it look strangely like old ivory. Mere painting, however skilfully performed, would not have given it its antique ivory look. The same artist had purchased one or two common, large, yellowish terra-cotta wine-jars. He drew on them classical figures, cut out the outlines a little with chisel and file, and smoothing the figures with sandpaper, also ivoried the whole by rubbing in colour. This was but a few hours’ work, yet the effect was startling. What had cost but a few francs would have sold for hundreds. I should add that with the aid of fine retouching flexible varnish this process could be very much facilitated. Any one who can draw or paint at all can try this experiment on any old piece of wood-carving, or on a common yellow coarse earthenware. Smooth the latter first with sandpaper, then rub in the colours. The same is applicable to old carving in marble.

All of these devices are of use to the restorer. As regards restoration of terra-cotta, the field is wide and profitable. Not only in Italy, but even in London, we may find for sale broken Etruscan vases or similar objects for a trifle, which are extremely easy to restore. These are generally of red or light yellow clay baked. If you have, let us say, a vase fractured, obtain clay of the same colour—if you cannot readily get it, take pipeclay—and colour it with a strong infusion of red or yellow, though this is not necessary if the exterior is black. Mix the clay well with glue or gum-arabic and alum-water, supply the missing portions, and let them harden. With a little care and practice, remarkable restorations may thus be made. I may here add that with this composition, bottles, decanters, and cups can be coated, which, when painted or rubbed in, exactly resemble Etruscan or other ancient pottery. To prevent cracking, they should first be painted with thick, coarse oil paint mixed with sand or umber, which forms a ground. Let it dry—the longer the better—and then rub in, thinly, the gum and clay. There is another composition of blanc d’Espagne, or whiting, and silicate of soda, which sets even harder, but which is a little more difficult at first to work, which may be used for such restoration. This can be directly painted on glass for a ground.

Majolica or Faïence can generally be sufficiently well mended with acidulated glue, but as the latter often communicates a dark stain, it is better to use for fine ware, or any which is to be used, the so-called Turkish cement. The best quality of this is made of the finest quality of gum-mastic dissolved in spirit. It is so tenacious that in the East gems are frequently directly attached by means of it to metal, and they will often break sooner than separate from it. Most chemists have for sale, or will prepare for you, some form of it. The silicate of potash and whiting can also be supplied by chemists; they should be mixed with great care, so as to form a medium paste, and then used rapidly and with skill, because this cement hardens very quickly. It is, however, a very powerful binder, and sets as hard as glass.

Having put together and cemented the broken pieces of a cup or vase, they must be kept in place till the cement dries. This is effected by means of many contrivances, regarding which the operator must employ some original inventiveness. Firstly, the pieces can often be simply tied, or attached by pieces of tape, or parchment, or paper glued on. In other cases india-rubber bands are useful. Again, bits of wood, or sticks and wires, are the things useful. A bed of wax is generally a sure guard. It is best to do this with great care, and not impatiently rely on holding the pieces together with the fingers till they stick. This is often the most difficult part of the whole operation; therefore it should be done well and deliberately. And here it may be remarked that, as in surgery, the most complicated cases of fracture may be studied out and adjusted; for which reason I dare say that skilful surgeons would be good menders of crockery, just as good astronomers are always good riflemen.

When the broken pieces are adjusted and all is dry, there remain the chips, hollows, ragged edges, and “hairs,” as the French call them, or lines of juncture, to be filled and smoothed. This is done with the cement which you employ, according to the quality of the material, either plaster and gum-arabic, silicate and whiting, or powdered chalk. Some experts succeed with white of an egg and finely powdered quicklime, which holds firmly, but which requires practice to amalgamate. Fill the cavities carefully, pressing the cement well in, as the Romans did, with a stick or point. When all is smooth, paint over the blank spaces and varnish with Sohnée, No. 3, or with a slight coating of silicate. Fine copal varnish is rather tougher or less brittle.

The most thorough process of all is to unite the fragments with a vitreous or metallic flux, such as the silicate—there are several of these—and then have the work baked or fired. It can then be painted with porcelain colours under glaze, and fired again. As this is very delicate, difficult, and expensive, few amateurs will care to try it. It is, however, perfect, and by means of it the most complete reparation can be effected. The Japanese do this simply with the blow-pipe, by means of which they fix enamel powders even on wood. This use of the pipe is also difficult, but the ancient Romans are said to have employed the process with most minor work. As a thread of glass will melt in a candle, and as fine-glass powder is equally fusible, it can be understood that under the flame of a blow-pipe the latter can often be melted so as to avail in restoration.

Crockery, or Faïence, and Porcelain.—“Crockery,” by which we commonly understand such ware as that of the blue willow plates, is far superior to terra-cotta, since its core or basis is thin, and very hard, and its gloss of a different description, and more incorporated with the body; or it is of a single superior body.

Porcelain differs entirely from the other two kinds of fictile ware, being an elaborate mineralogical compound, its base being kaolin, a friable, white, earthy substance, requiring great care in its preparation, and petunse, or feldspar, which is united with the kaolin. The result is a very delicate and beautiful diaphanous ware, or one through which light passes to a limited degree. Both crockery and porcelain are far more difficult to mend, owing to the impossibility—particularly with the latter—of making fractures disappear.

The first and most simple process of mending both kinds of ware is to make small holes with a drill along the edges of the fracture, and then, adjusting the fragments, bind them together with wire. M. Ris-Paquot claims that “the honour of this discovery belongs properly to a humble and modest workman named Delille, of the little village of Montjoye, in Normandy.” But the archæologist will say of this claim, as the English judge did of a similar one, that the plaintiff might as well apply for a patent for having discovered the art of mixing brandy with water, since there was probably never yet a savage who had wire, or even string, who did not know enough to mend broken calabashes, jars, and pipes by this solid method of sewing. From the time when large earthen punch-bowls were first used in Europe, we find them mended with silver wire. It is needless to devote whole pages with illustrations, as M. Ris-Paquot has done, to show how to effect such mending. The holes are made with either a bore or hand drill, such as can be bought in every tool shop. If the reader will obtain one and experiment with it on any penny plate or broken fragment, he will soon master all the mystery. The wire is made fast by a turn with a pair of nippers or pincers. Before fastening, wash the edges of the ware with white of egg in which a very little whiting, or finely powdered lime or plaster of Paris, has been mixed.

I may here observe that the wire for china-drilling should be half round, or flat on one side. To prepare this, take brass wire, say a length of about two feet, and, holding an old knife, draw the wire firmly and steadily against it.

There are endless cements for sale by chemists, all warranted perfect, to mend glass and china, and most of them do indeed answer the purpose very well, for nature has given us not a few materials wherewith to repair accidents. Thus, even boiling in milk will often suffice to reunite broken edges. But I believe that of all, the Turkish cement already described, which is made of gum MASTIC (a term improperly applied in France to putty, by Americans to lime-plaster on houses, and by Levantines to spirit with resin in it), is the most adhesive and resistant to heat, cold, or moisture.

The art of mending does not consist so much of knowing what to use for an ADHESIVE (since, as I have said, every chemist’s shop abounds in these) as in skill and tact with which fragments are brought and kept together, missing portions supplied, and in knowing the substance with which to fill a blank. There are cases in which, when a hole has been knocked in a china or glass plate, it can be drilled out round, and a disc of the same substance or colour, or even of another, inserted. This is almost an art by itself, and by means of it very singular and puzzling effects may be introduced; as, for instance, when a number of holes are drilled in a white china plate and then filled with discs of coloured china, agate, coral, &c. In the East, turquoise and coral beads are often thus set into porcelain, as well as wood. The mastic or acidulated glue is used to make the objects inserted hold firmly.

As the smoker, when he breaks his pipe across the stem, has it repaired with a short silver slide or tube, so when a china jar is broken across the neck, the reparation can be concealed by a silver collar, which is sometimes a great improvement; as, for instance, when the head of a china dog, or even of a china man, is taken off. But in a great many cases, or in all where this kind of concealment is advisable, it may be made, like Cæsar’s wife, beyond suspicion, by making the collar or concealing ornament, or leaf or flower, of silicate and whiting so as to resemble the ware itself, which can be done very nicely.

Silicate of Soda is sometimes sold in the form of a dry solid, which is placed in a little vinegar, and warmed. When dissolved it can be used ad libitum. It is often used as a glaze for stone.

There is a curious old story about mending broken crockery by means of magic—or rather by deceit—which, though not of a practical nature, is at least amusing. It is partially told in a book published about 1670, entitled Joco-Seriorum Naturæ et Artis Magiæ Naturales Centuriæ Tres. It happened once in Mergentheim that there was a great fair, when the whole courtyard of the palace was full of earthenware vessels for sale ab assidentibus muliebibus (by attendant women). Seeing this, the Prince of Mergentheim went about among these women, and so arranged it that they divided all their stock into two parts, or exact duplicates, half of which they hid away, while the other half was exposed for sale. While at dinner the Prince spoke much of magic, and professed to be able to produce such a delirium in people’s minds that they would act like lunatics. “Thus, for instance,” he said, pointing casually out of the window, “you see all those women. I can drive them mad at once.” Whereupon one who was present wagered a handsome carriage and four horses that the Prince could not do it. The latter smiled, waved his hand, and uttered a spell, when lo! all at once the market-women began, bacchantium more—like raging Bacchantæ—to attack their crockery with sticks and stools, and hurl it about, and dash it to pieces.

The one who had betted the chariot protested that it was a trick arranged beforehand. The Prince replied, “Well, the pots are all broken. If I can mend them again by a spell, wilt thou then believe?” The other said, “Most certainly.” Then the Prince waved his wand and said, “It is done. Let us go down into the courtyard and see.” And when there, sure enough they found the pots all whole again—at least they discovered others exactly like them in their places.

The legend continued that the Prince, though he kept the carriage and horses as a trophy, liberally paid for them. The author of the Tres Centuriæ, who does not record the secret of the little arrangement, declares that he does not know whether it was all done by a fraud or by magic. If it was the latter, I regret that the incantation by which broken crockery is mended is now lost. The most powerful spell known to me is Recipe Gummæ Mastichæ duæ unciæ cum Spirito Vini fiat mixtio—that is, mastic cement. It is generally combined with sturgeon’s bladder glue.

This cement answers very well for glass. One of the old recipes, which was very good indeed, is thus given by Johannes Wallburger (1760):—“Take finely cut and a little powdered sturgeon’s bladder” (still sold by all chemists), “soften it all night in spirits, add to this a little clean and powdered mastic, boil it a little in a brass pan. Should it become too thick, add a little spirits.” This may be also used for many other purposes.

A strong but coarser adhesive, especially for crockery and stone, can be made as follows:—Take old and hard goat’s milk cheese, and warm it in hot water till it forms, by pounding, a mass like turpentine. Add to this, while grinding, finely pulverised quicklime and the well-shaken white of eggs.

I do not hesitate to give a variety of such recipes, because in every one the artist will find valuable suggestions for other purposes than simply glueing broken articles together. This latter is a valuable “filler” for many purposes. Glue was formerly made into a strong cement by boiling it for a time in water, but before it had become incorporated with the water, the latter was poured off and strong spirits substituted and stirred well in.

A very popular old cement for crockery, of which there were several variations, was made by mixing glue, turpentine, ox-gall, the juice of garlic, and sturgeon-bladder, tragacanth, and mastic. All of this singularly smelling mixture was put into a pan and boiled in strong spirits, such as whisky, then kneaded on a board under a roller, again boiled with more spirits, yet again rolled, and this was repeated a third time, and then cooled till it could be cut into cakes. When these were to be used they were again steeped in spirits. But with this cement, glass or metal could be most firmly attached to wood. I confess that I have never tried it, but it was evidently a very strong cement.

Another of these somewhat complicated recipes for crockery, glass, and porcelain, which I find in the Tausandkünstler, 1782, is as follows:—Half an ounce of finely cut sturgeon’s bladder, two teaspoonfuls of alabaster powder or gypsum, quarter of an ounce of tragacanth, one teaspoonful of silberglatt, two of powdered mastic, two of frankincense, two of gum-arabic, one of Marienglas, one tablespoonful of spirits of wine, one of beer-vinegar. Boil it and stir, and apply. Any drops sticking to the mended article may be removed with vinegar. When it is to be used again revive it by heating, adding spirits of wine and beer-vinegar. The gum-frankincense is here worth noting.

A common cement for mending broken glass or china is prepared as follows:—To two parts of gum-shellac add one of turpentine; boil them over a slow fire, and form the mass into small cakes before it dries. To use it, warm with a lamp. To mend ivory or wood, take a cake and let it dissolve in spirits of wine.

A very strong cement is made as follows:—Take one ounce of finely powdered mastic dissolved in six of spirits of wine and two ounces of shredded sturgeon’s bladder dissolved in two ounces common spirits; add one half ounce of gum-ammoniac as it hardens; warm it when it is to be used. This is as strong a cement as can be made.

Defects, cracks, and repairs in porcelain, &c., may often be concealed as follows:—Paint the spot with silicate of soda, not too much thinned, and dust it over before it dries with bronze powder. This will set so hard that it may be polished with an agate burnisher.

It is also possible that many of my readers have heard of gesso painting, an art perfected by Mr. Walter Crane. This consists of painting with plaster of Paris in solution, with the point of a brush, depositing the soft paste in relief. The same principle is applicable to painting in silicate and whiting on glass surfaces. By means of it decoration can be given to any glass bottle or other object.

Lime enters into the composition of many cements, the simplest being the mortar formed by its admixture with water. But the quality of this is very much determined by that of the lime. The chunam of India, which resembles white marble or a fine white stone, is made of sea-shells burned to lime. A wonderfully hard, fine, white cement used by the Romans for their best mosaic-work, and which set with great rapidity, was made of shell-lime with the white of eggs. I have found the same composition worthless when made with inferior stone-lime.

A good cheap cement for porcelain and glass is combined as follows:—

Starch or wheat flour	8
Glue	4
Purified chalk	12
Turpentine	4
Spirits of wine	24
Water	24

Pour a part of the spirits and water mixed on the flour and chalk, add the glue, boil it down till the latter dissolves, and stir the turpentine into the whole. This can be used to make artificial wood with shavings or sawdust.

A very good cement for porcelain, and one which is colourless, is made by cutting the finest clear gelatine into bits, and dissolving it in vinegar of 50°, stirring it in a porcelain vessel until well mixed. When cold it will harden, but softens under the influence of heat, when it may be applied to the broken edges of the porcelain, which are to be pressed together. It will be perfectly hard within twenty-four hours. It is to be observed that the art of keeping such joined pieces together is the most difficult problem in mending. This cement is widely applicable to many objects, and also admits of considerable modification and additions, like all cements. As it is colourless, it may be combined with ivory dust, or white powders of baryta, magnesia, whiting, &c., to form artificial ivory with glycerine. With sturgeon’s bladder it makes a still stronger cement.

Lehner observes that glue has the property, when combined with acid chrome salt (sauren chromsalzen), of losing its solubility when exposed to the light, so that it can be used as a cement for broken porcelain and glass. If the juncture is to be invisible, take the purest white gelatine; otherwise the cheaper gilder’s glue will answer. To prepare the chrome glue, dissolve the gelatine or the glue in boiling water, then add the solution of double chromic acid alkali, or the red chrome alkali of commerce, stir it well up, and put it into tin boxes.

The formula is:—

Gelatine or gilders’ glue	5-10
Water	90
Red chrome alkali	1-2
Dissolved in water	10

To use, warm the cement, apply it to the broken glass, which must then be exposed for several hours to the sunshine.