MENDING GLASS WITH SEVERAL ALLIED PROCESSES APPROVED CEMENTS—SILICATE OF SODA

Putty is naturally the first cement which suggests itself in connection with the mending of glass, since this latter material is most familiar to the world in the form of windows, although in many places—as, for instance, Florence, where it is called mastico and pasta—it is little used or known. The word is from the French potée, which also means a potful. It is very useful, not only for setting glass-panes, but for filling holes in wood, and forms a part of certain mixtures as a cement for moulding ornaments. It may be weak and brittle, or else strong and very hard, according to the manner in which it is prepared. It is commonly made by combining chalk in paste, with water, with linseed-oil; other powders are also used. In America it is made with pulverised soap-stone and oil. Its excellence depends on the quality of the oil and the care with which it is kneaded. It should be kept in a damp cellar, in wet cloth or under water. Should it dry and become brittle, fresh oil must be added.

“To take hard old putty from glass window-panes, cover it with a mixture of one part of calcined lime, two of soda, and two of water” (Lehner). Oxide of lead combined with oil makes an excellent but yellow putty. It sets very hard.

The white or grey oxide of zinc combined with linseed-oil or linseed-oil varnish makes a cement which is used for making glass adhere to wood or metal.

Thick lacquers, such as copal or amber, may be used instead of common varnish with better effect, and the composition is better when calcined lime or oxide of lead are added. The excellence of the cement depends on the degree to which the ingredients are amalgamated or rubbed in together; and this rule holds good for all similar mixtures.

Varnish, or heavy or “flat” lacquer of copal or amber, forms of itself a strong adhesive, with the only drawback that it takes a long time to dry.

A very good cement for glass (Lehner) is as follows:

Gutta-percha 100

Black pitch (asphalt) 100

Oil of turpentine 15

This is a glue of general application, and specially good for leather and mending shoes.

The reader who would thoroughly study the subject of glass may consult Die Glas-Fabrikation, a very admirable work by Raimund Gerner, glass manufacturer; A. Hartleben, Vienna and Leipzig, price 4s. 6d.

Small triangles of sheet tin or iron are often used to fasten panes.

The mending of broken glass is in most cases much the same as that of broken crockery or porcelain. The cement made from mastic, or mastic combined with sturgeon’s bladder, or generally of silicate with whiting, is the proper adhesive. As silicate of soda is simply liquid glass, it can be employed to fill spaces or to make glass; but, owing to its sticky nature, it is hard to manage. This may be often effected by first preparing a layer of soft paper, on which successive coats of silicate are laid. When dry the paper can be washed away.

Silicate of Soda has become of such importance that a French work on mending fictile ware is almost entirely limited to its use as a binder, when combined with whiting. Water-glass was long supposed to be a modern invention, till some one found it described in Van Helmont’s works, A.D. 1610. But I have found it also in the Joco-seriorum Naturæ, 1545; in the Magia Naturalis of Wolfgang Hildebrand, which is of the same time; and, finally, by Paracelsus (Liber de Præparationibus), where he describes it as Destillatio Crystalli. And the author of the Joco-seriorum speaks of soft glass as a thing which had been treated by several writers.

According to Wagner there are three kinds of soluble glass—(i.) the soluble potash glass, 45 silex, 3 charcoal, 34 carb. potass.; (ii.) soluble soda glass, 100 pts. quartz, 60 cal. sulp. soda, 15 of charcoal; (iii.) double soluble glass, 100 quartz, 22 cal. soda, 28 carb. potass., 6 wood-coal. Water-glass combines well with any “indifferent” powder, such as powdered glass, to make a strong cement. To powder glass, heat it red-hot, drop it into cold water and pulverise it. It will become as fine as flour, and in this state combines with gum-arabic, or glue, or gums to make a powerful glass-mender. Mixed with powdered glass, oxide of zinc, or whiting, powdered marble, calcined bone, plaster of Paris, wood-ashes, &c., it can be worked like putty. Mixed with colours it is used for stereochrome painting, a kind of fresco.

Missing pieces of glass, such as leaves from a chandelier, can be easily replaced with water-glass, and all cracks or defects glazed over with it.

This mending is allied, however, to certain processes in art which are so interesting that I venture on a description of them.

A great deal of mending and restoring in glass can be effected by means of the blow-pipe and spirit-lamp or gas-flame. Difficult as this may sound, it is not only an easy, but also a very curious and entertaining, occupation. In any city an expert or workman may be found who would give a few lessons. I have very often been impressed with the fact that so little artistic invention or originality is found in glass-work. Even the far-famed Venetian work is extremely limited, and “mannered” or conventional, compared to what it might be.

The following is an old recipe for repairing glass:—Take finest powdered glass, best mastic, with equal parts of white resin and distilled turpentine. Melt all well together. To use, gradually warm it and then apply.

Quicklime and white of egg, intimately rubbed into one another on a flat surface, make a good cement for ordinary glass or pottery.

The cement of gum-arabic is much stronger when made as follows:—Take gum-arabic and dissolve it in acetic acid (vinegar) instead of water. It must be melted in a hottish place, as it will in that case be much better. The finest quality of sheet-gelatine makes a transparent glue, invaluable where colour is to be avoided.

To mend a cracked Glass Bottle or Decanter.—Heat the bottle, pressing in the cork, till the hot air within expands the cracks, which must be at once filled with the liquid glass. Then, as the water-glass is driven in by the pressure of the outer air, as the bottle cools the cracks are closed.

You cannot well mend a broken looking-glass, but something can be done with the large pieces. Varnish or paste a piece of paper and lay it on the quicksilver. Then with an American glass-cutter, price one shilling, or a diamond-cutter, divide them into squares for small mirrors. Two of these of equal size can easily be converted into a folding kaleidoscope (not described by Brewster in his work on the Kaleidoscope). Lay the two pieces face to face, and paste over the whole, on the quicksilvered side, a piece of thin leather or muslin. When dry, with a penknife, cut a slit down between the two on three sides. It will then open and shut like a portfolio. This may serve as a travelling, looking or shaving glass, but it is very useful to designers of patterns. Place the glass upright on a table at a right angle, or more or less, and lay between the mirrors any object or a pattern, and you will see it multiplied from three to twelve times, according to the angle. Beautiful variations of designs can thus be made, ad infinitum. They may be used as reflectors, when placed behind a light.

Take such a piece of looking-glass and lay a piece of paper on the back, and then with an agate or ivory point write or draw on it, but not as hard as to break the silvering. Then turn it to the sun or a strong light, and let the reflection fall on a white surface. Though nothing be perceptible on the face of the mirror, the writing will appear in the reflection.

Glass is engraved as metal is etched; with this exception, that, instead of sulphuric or nitric acids, fluoric acid is used. Both glass and china can also be directly etched with a steel point, aided by emery powder; which latter art I have never seen described, but which I have successfully practised. It is fully set forth in my forthcoming work on “One Hundred Arts.”

Malleable glass, or at least that which does not break easily when let fall, is prepared by dipping the objects made from it, while quite hot, into oil. I conjecture that panes of window-glass thus prepared would not be broken by hail, as I have observed that plate-glass is not.

It sometimes happens that goblets of thin glass—especially those which have had a peculiar kind of annealing or tempering—ring beautifully when blown on so as to vibrate them. The effect is almost magical on one who hears it for the first time. I mention it that the reader may, when he finds old Venetian or any other thin glass goblets for sale, see if there be not among them a finely ringing one. An organ could be thus made to play by wind. With regard to music on glass, take any ordinary bottle, and by rubbing on it a cork a little wetted you can, with a little practice, produce a startling imitation of the chirping, and even warbling, of birds. I knew one who could thus imitate to perfection nightingales and call forth responsive songs. The effect depends in a degree on the quality of the cork, and also that of the glass. With a violin-bow very musical sounds may be drawn from the edge of a pane of glass. It seems as if these methods might also be developed into musical instruments. It is well known that tubes of glass suspended when a candle is placed beneath them give forth musical sounds, often of great richness and strength. There are also the musical glasses, which may be played in two ways, either by rubbing the edges with a wetted finger or by filling the glasses more or less with water till an octave is formed, and then tapping them with a stick of wood. All of which has, indeed, nothing to do with mending glass, yet which may not be without interest to those who wish to learn all its qualities.

Among Glass Cements in common use which can be recommended are the well-known Polytechnic, also the Imperial Liquid Glue (no heating required), Hayden & Co., Warwick Square, London. There is also a very good glass cement made and sold by Keye, filter-maker, Hill Street, Birmingham.

The Venetians made ordinary glass goblets very beautiful by painting on them in relief with a substance which I suspect was in some cases a form of silicate, or else with a kind of paint which was not enamel, yet which seems to have been partly vitreous. It rather resembles oil paint with glass powder, but I doubt if it was this.

Working in glass implies the mending and restoration of stained-glass windows; that is, of painting on glass and a study of designs. Of all this there is almost a literature. Among other works I can commend A Book of Ornamental Glazing Quarries, by A. W. Franks, £1, 1s.; Divers Works of Early Masters in Ecclesiastical Decoration, by Owen Jones, £3, 10s.; Westlake’s History of Stained Glass, vol. i., Fourteenth Century, 13s. 6d.; vol. iii., Fifteenth Century, 18s., published by Batsford, 52 High Holborn. At Rimmel’s, in Oxford Street, the reader can generally obtain these, and all works on similar subjects at prices much below the original cost.

A mending cement for glass is made as follows:—

Common cheese 100

Water 50

Slacked lime 20

This is found in many books of recipes. It must be observed that the cheese is to be for sometime carefully pounded with the water till quite soft, and the lime then very quickly stirred in. This is not only useful to mend glass, but can be applied to many other purposes. The cheese is best when fresh.

Caseine (or pure cheese) can be combined with ease with liquid silicate of soda (Lehner), and thus forms a very strong cement for porcelain or glass, or any other material. Fill a flask with one-fourth of fresh caseine to three-fourths of silicate, and shake it thoroughly and frequently.

Another formula is as follows:—

Caseine 10

Silicate of soda 60

This must be used very promptly, and the article mended dried in the air.

A CEMENT which may be used in several combinations is made by dissolving fresh acidulated caseine (made by adding vinegar to milk, and carefully washing the deposit) in a very little caustic lye. It must be kept corked in bottles.

These caseine or cheese or curd cements hold well, but do not well resist water, except in powerful combination.

The excellence of cements depends to a great degree on the quality of the materials and the scrupulous observance of care in making. Thus for the following, for glass:—

Glue 200

Water 100

Calcined lime 50

in which we have one of the commonest and oldest formulas, the value depends on “the make-up” that is, the glue must be left in cold water for two days, then boiled in a balneum mariæ, or a double kettle, in lukewarm water; that is, it must not boil, or the glue will be weakened.

The so-called Diamond or Turkish Cement, for glass or any other fine work, has been known since early times as incredibly strong. Its formula, according to Lehner, is as follows:—

I. Sturgeon’s bladder 20

Water 140

Spirits of wine 60

II. Gum-mastic 10

Alcohol 80

III. Gum-ammoniac 6

These are three separate portions, No. I. being prepared by warming and filtering. The gum-ammoniac is reserved from the others, and added after they are mingled.

A strong base for a cement for glass, as well as wood or stone, is made by gradually stirring finely sifted wood-ashes into silicate of soda, or strong acid glue, till a syrup-like substance results. In America the best ashes for this purpose are those of the hickory. Perhaps beech wood yields them equally good.

There is a Diamond Cement which is of special value to attach gems to rings or metal, to make coral or pearl or ivory adhere together, and, in short, for all fine work where a very strong adhesive is required. It is as follows:—

Sturgeon’s bladder 8

Gum-ammoniac 1

Galbanum 1

Spirits of wine 4

The sturgeon’s bladder is cut into small pieces and steeped in the spirits, and the rest, in solution, then added. It must be warmed again when used.

As this cement will bear long exposure to moisture before being at all injured by it, it can be used as a medium for painting on glass, and thereby producing effects very little inferior, either as regards beauty or durability, to glass itself. The experiment can be easily tried, as any chemist can make up the recipe. When finished, the painting can be coated with liquid silicate of soda, which will give it all the property of glass.

A lime cement for glass is made as follows:—

Calcined lime 30

Litharge 30

Linseed-oil varnish 5

Jewellers’ cement. Extremely strong:—

Fish-glue solution 100

Mastic varnish (pure) 50

The fish-glue must first be dissolved in spirits of wine.

To join Glass and Metal, &c.—Stir slacked and powdered lime in hot glue. This sets as a very hard substance. It can be extensively modified and varied for many substances, and used for painting.

Cement for glass:—

Gum-arabic 50

Sugar 10

Water 50

Oil of turpentine 10

The gum, sugar, and water are first carefully combined, and then the turpentine well stirred with the mixture.

Salle’s cement for glass:—

Muriate of lime 2

Gum-arabic 20

Water 25

Not commended by Lehner, as being too soluble. To close bottles:—

Powdered resin 6

Caustic soda 2

Water 10

To be thoroughly mixed and left for several hours. Before using, stir well into it eight to nine parts of calcined plaster of Paris. This will in half-an-hour take firm hold or “set,” and is waterproof. A good filler for cracks.

The reader who desires to be perfectly informed as to glass in all its relations can obtain, by application to J. Baer, Rossmarkt, Frankfort on the Main, Germany, a catalogue which is perhaps the most extensive on the subject ever published.

Coloured or stained glass windows may be repaired or made by the following process, which has the advantage of being quite as durable as any in which the colours are burned in:—Take two panes of glass, and paint on one your pattern with fine varnish and transparent colour mixed. When dry, go over the whole, with a broad, soft brush, with a liquid mastic cement, which must be quite transparent and thin. Any transparent strong cement will serve, but it is advisable to use the mastic in all cases as a narrow border and at the edges. If you have an engraving, especially one on very soft spongy paper, take a pane of glass, cover it with a coat of varnish, and just before it dries press the engraving face down, on it. When quite dry, with a sponge slightly damped and the end of the finger, peel away all the soft paper, leaving the lines of the engraving. These may now be coloured over, with even very little skill and care. A very good effect may be produced, so that a very indifferent artist can in this way produce very tolerable pictures. Then, to better preserve this, double it with the other pane.

By painting and shading also on this second pane, as I have discovered, very beautiful and striking effects of light and shade can be developed, so that this forms, as it were, a new art by itself. This will remind the reader of the porcelain lamp-shades, which so much resemble pictures in Indian ink; but the effects of the double panes are more singular and far more varied. There may be even a third pane employed. As the materials for this art are far from expensive, and as it is extremely easy, I have no doubt that it will be extensively practised. Protecting one glass picture by another is not a new art; but I am not aware that the obtaining a series of lights by thus reduplicating the panes has been practised.

A modification of it is as follows:—Cut out several panes, corresponding to the size of the two glass covers, of quite transparent paper or parchment, prepared by rubbing with oil or vaseline, lard, or the like. Paint on these the required modifications of the picture. The advantage of this is, that a great many shades can thus be given in a thinner space, creating an astonishing effect. As this is not at all a mere imitation of stained glass, and as it produces effects not to be found in the latter, it may rank as an art by itself. The chief of these effects is relief, especially shown in the human figure. But the most extraordinary are the variations of chiaroscuro which it affords, by availing himself of which the artist may create or obtain striking suggestions for oil or aquarelle pictures; for these transparencies can be so infinitely and ingeniously varied that no one can fail to derive from them many ideas.

This may be tested by simply preparing any picture, say of a statue, a castle on a rock, or a face. Cut out from sheets of the same size in very transparent paper a series of shadows adapted to it, and adjust them. They may be all in monochrome or one colour, or in many hues. They may range, with proper care, from almost imperceptible shadow to opaque black. By beginning with only two stencils or shaded pictures—for as regards these the artist must be guided by his own skill—and gradually increasing the number, the proper adjustment will soon be found. I advise the beginner in copying to proceed from monochrome to two colours before attempting many. Teachers in aquarelle will find that such copies are—after a certain degree of proficiency shall have been obtained—much superior to those commonly used, as they come nearer to nature.

The most perfect form of this curious art is an improvement which, I believe, is my own invention. This consists of introducing leaves of painted mica between the two glasses. In this way four grades or tones of colour and light and shade can be made in a picture. Mica-leaves can be made into one by using mastic cement. Rub the edges with emery-paper to roughen them.

As I have already intimated, the materials for this work are so cheap and the process so easy, that all which I here assert may be at once verified by the outlay of a few shillings, with a few hours of time. It is, in another form, the same thing as arranging lights around a statue in a dark room, but adapted to all kinds of pictures.

As a Latin poet has declared, “It is an easy thing to add to arts,” when a beginning has once been made (“Inventis facile semper aliquid addere”), so I will add to this a curious discovery in glass made by me in Venice a few years ago. I was being taken by Sir Austin Layard over his celebrated glass-factory. It was he who, with the aid of Sir William Drake, first revived the almost forgotten manufacture of glass in Murano. While standing with him by a furnace watching a workman skilfully forming ornaments in glass, it suddenly occurred to me that the Chinese were said to have possessed in remote times an art, now lost, of making vases or bottles which appeared externally to be quite plain, but on the surface of which, when red wine was poured in, patterns or inscriptions appeared of the same colour. It at once occurred to me that this could be perfectly effected by making a bottle, on the interior of which the ground should be of considerable thickness, say half-an-inch, while the inscription or pattern would be no thicker than ordinary window-glass. Then if the whole exterior were to be lightly ground on a wheel or sandpapered, the difference between ground and pattern would not be perceptible until red wine or some highly coloured fluid were poured in, when the pattern would at once show itself.

Sir Austin Layard was so much struck by the suggestion that he sent at once for his foreman, Signore Castellani, who said that he had heard of such bottles, but always supposed it was a fable. He, however, at once admitted that they could be made as I proposed, but added that the expense would be so great as to render the invention practically useless.

It has, however, since occurred to me that such bottles could be made, and cheaply, as follows:—Take a Florence flask, and divide it into two parts with a diamond, using a saw for the bottom. Then on the sides within place the ground. It could be made of silicate of soda and powdered glass or flint, or even of white wax, hardened with powdered glass. Close the bottle with silicate, and grind the whole.

When any glass has been broken and mended, the fracture still discernible may be thus concealed by grinding the surface, and in many cases by surrounding it with a ring or tube of metal, also by one of silicate, or with an ornament formed with it.

A glass stopper when too large can be easily filed down to fit. Should the neck of the bottle be too narrow, it can also be enlarged by the same process. When the rim of a goblet is fractured, it can be ground down on a grindstone. I have done it with a file.

A pane of glass can be somewhat rudely cut into shape with a pair of strong scissors, under water. In this, as in other things, practice leads to perfection.

An old method of effectually closing bottles of wine was as follows:—The edge of the opening on the top was ground down on a stone, and a small disc of glass was exactly fitted to it. Heat was then applied till both were in partial fusion and the cover was welded to the bottle. A little powdered glass would aid the fusion, or it could be effected with silicate without heating. The process is the same as using glass stoppers, rather sunk in, and sealing up with silicate.

A broken champagne bottle is not easily mended, but I have seen one curiously utilised. The bottom only had been broken, and it was cut off round and evenly with a file. Within it there hung from the cork by a cord a very large nail or small bolt of iron. Thus prepared, it made a capital and appropriate dinner-bell. Here in Italy I have often seen bells made of crockery or terra-cotta; their tone is better than would be supposed.