Decorative glass processes

Front matter

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%uiLDiH(j Dept.

TIbe “Westminster” Series

Preface

The present volume finds its reason for existence in the fact that no book has yet appeared dealing collectively with the various methods of glass decoration which it includes. We have many good books on Stained Glass ; there are two or three works which touch lightly on Embossing, but nothing dealing with it in a thoroughly practical way, while nothing whatever seems to have appeared in print regarding Brilliant Cutting. One or two of the minor processes, such as Sand Blast, Crystalline, etc., also make what is practically a first appearance here.

The nomenclature employed is that of the workshop. To talk of “ embossing ” glass certainly seems absurd, but that is the accepted term, though its only excuse is that the acid produces a slight hollow on the surface of the glass. “Etching” is a much more satisfactory term in every respect, but “ embossing ” has become so sanctioned by use that it is useless to think of overthrowing it. So, too, with “ brilliant cutting,” which has no connection with diamonds, but is only a development of the glass engraving process which has so long been employed in the decoration of table and other hollow glassware.

viii PKEFACE

The following pages are the result for the most part of the practical experience of the writer either as designer or executant, or both. In one or two of the less important processes information which is not the result of practical experience has been obtained from reliable souices.

ARTHUR LOUIS DUTHIE.

“ Came lot,”

Kouxdhay, Leeds,

Contents

PAQB

Preface . vii

List of Illustrations . xi

Chapter I

Practically every kind of glass which has ever been made can he turned to account in some decorative process, whether it be the simplest and cheapest sheet glass or the most beautiful “ antique ” — we have seen broken bottles used with good effect in leaded figure work. The number of ornamental glasses grows from day to day, so much so as to show at the present a very formidable number. Many of them naturally are somewhat limited in their sphere of usefulness for various reasons, having been introduced in some cases in response to a demand for novelty and artistic effect. The latter demand is rather poorly met on the whole, though there are varying opinions on the point, and many people are perfectly satisfied with what to others is little short of an abomination. The majority are naturally intended to be seen by transmitted light, but a number of them, opalescent or iridescent in character, are also useful when placed so as to reflect light, and advantage is taken of this fact to turn them to a number of purposes which they were not at first calculated to fulfil. Consider¬ able ingenuity has been displayed in one or two instances in taking advantage of and enhancing these qualities, and very successful results have been attained.

A description of the glasses in most general use in the processes which we propose to study, with notes of the manner in which the}'- are most successfully used, will be necessary here, along with an approximate price list to show their relative value. Artistic value and commercial value do not in all cases correspond, as is perhaps to be expected, but with a few exceptions they may be said to do so. Design is, of course, the supreme factor in this respect, a good design in cheap glasses appearing more valuable than a poor design in which more valuable and much more beautiful glasses can only look tawdry. Generally speaking, a small quantity of the more valuable glasses goes a long way, and judicious treatment in this respect often admits of their use when economic considerations would otherwise forbid. The different processes by which they are manu¬ factured are of great interest as accounting in most cases for their peculiar characteristics and showing how these are produced, but it will not help us in any way to do more than mention them in passing.

The simplest and cheapest is, of course, Sheet glass, which in spite of its simplicity, or perhaps because of it, has a wide range of usefulness. It is made by blowing in cylinders 5 feet or more in length, which are afterwards split open and flattened out in a kiln. The majority of it comes from the Continent, principally Belgium. Its different thicknesses are distinguished as 15 oz., 21 oz., 26 oz., 32 oz., etc., these figures representing the approximate weight per superficial foot. It is divided by selection into first, second, third, and fourth qualities according to its freedom from waves, air-bubbles, and other defects. It is largely used for leaded lights, where transparency is required at a low price, and also for the cheapest class of embossed and brilliant cut work. Obscured Sheet glass is also used for embossing and brilliant cutting. It was at one time produced by means of hand grinding, but is now done entirely by means of the sand-blast. Sheet glass is also Enamelled in various stencilled patterns with white enamel and stained with silver stain, but, owing to the hardness of the metal, a very strong stain is required. This Enamelled Sheet had a considerable vogue at one time for screen work in private houses and elsewhere, but has now been superseded, except for repairs, by embossed work or leaded lights.

Patent Plate is made by grinding and polishing selected sheet glass on both sides, so removing the wavy surface which would otherwise have the effect of distorting images seen through it and producing what is practically thin plate glass. For a good class of leaded lights for living rooms it is much superior to sheet glass as eliminating distortion and is frequently used on that account. There are, however, people who ask for sheet glass because of the quaint effect produced by the distortion, and who even welcome the use of the now almost obsolete Croicn glass in order that the distortion may be more marked. Crown glass is made in flat discs of about 4 feet diameter by a “ spinning ” process, the metal being changed from a bulb shape to the disc by the action of centrifugal force. The result of this spinning is that all the waves on the surface are curvilinear and concentric, while the centre of the disc where the “ pontil ” is broken off shows a big bull’s-eye knob, which used to be regarded as waste, but is now sought after for leaded light work.

llougli Cast Plate is produced by rolling and can be had in thicknesses of \ inch, § inch, J inch, and upwards. It is frequently used for skylights, painted and stained in various styles, and can be bent to practically any curve to fit the spherical surfaces of domes, etc. It answers very well for painting and staining, the metal being softer than sheet glass, and some very good and varied effects can be pro¬ duced with it. It is non-transparent and therefore recom¬ mends itself for use in ceiling lights, etc., where there is an external glass roof the frame of which would show badly through a clearer glass. There is practically no limit to size. It can be embossed with white acid and has been tried for brilliant cutting, but here its wavy surface renders it quite useless, destroying the outline of the design, which is of course dependent upon a regular level surface.

Patent Polled Plate is also non-transparent, and one side shows a series of corrugated ridges about Txg inch apart. These give it a mechanical look which makes it less useful for decoration, but it can be had with stained spot diapers upon it, which make it more attractive. Indeed this is the only form in which it may be said to enter the field of decorative glasses at all. It is useless for leading, embossing, or brilliant cutting. It is one of the least trans¬ parent of all colourless glasses, but it transmits a wonderful amount of light, which it diffuses very well, and so is useful from a utilitarian point of view for screens and borrowed lights.

Polished Plate glass is made from rough cast by grinding and polishing with emery and rouge. Its principal use from our point of view is in embossing and brilliant cutting. In size it is, of course, similar to rough cast, and can be had in sheets as large as 12 feet by 10 feet, or even larger when specially required, as, for instance, in shop windows — the record size at present is somewhere about 20 feet by 14 feet. In thickness it ranges from x%, T5¥, | inch

upwards. It lends itself readily to staining, being the same metal as the rough cast which we have already noted, and staining is occasionally used to enhance the effect of embossed and brilliant cut work. For leaded lights it is occasionally cut into more or less elaborate forms and its edges bevelled, when it gives a very brilliant though rather hard effect. Plates of almost any size can be embossed, though the difficulty and risk are naturally very great in the case of a large plate. In brilliant cut work the limit of size is about 4 feet square for average work — beyond that size only very simple designs, such as straight lines, spots, etc., which can be done without swinging the plate round, are possible.

The remaining glasses which we have to consider are mainly— some of them entirely— used for leaded and painted work. Of these the commonest is Rolled Cathedral, which is produced in sheets from 5 feet to 7 feet long and 28 inches wide. This is made in white, in tints, and in a variety of more or less pronounced colours, a large propor¬ tion of which cannot, from an artistic point of view, be commended. It is non-transparent and can be used wherever a moderate amount of obscurity is required for screens, etc. For painting and staining the white and tinted varieties are most useful. The white stains very well, as also do the greenish tints, but the yellowish tints are not so susceptible to the action of the silver. For cheap leaded light work it is extremely useful on account of its variety of tints and the ease with which it can be cut,

D.G.P.

C while its uniform thickness makes it very easily handled in leading.

Double rolled cathedral is a later introduction. It is more brilliant, the wavy surface being rather more open, and a little more transparent than single rolled. It is made in white and tints, and for painting and leading can be used in the same way as the single variety.

Muffled is practically a sheet glass, being blown in cylinders in a similar fashion. It is distinguished by a peculiar rippling surface which is rather more marked on one side than the other, and which frequently varies con¬ siderably in the length of a single sheet. This surface is produced at an early stage in the process of making, by blowing the bubble of glass into a mould, the interior of which is marked with the desired pattern in what might be called a compressed form. When the glass is removed from the mould and stretched to the full-sized cylinder, the pattern becomes distended and loses some of its regularity, the upper part of the cylinder naturally, through the weight of the lower part, having the pattern more smoothed out. It is very translucent and diffuses light well, while, in its rougher varieties at least, it makes a rather more effective screen than Rolled. Its range of colour is similar to Rolled, and it is equally useful for painting, staining, and leading. Its greater brilliance renders it more popular than Rolled for the cheaper class of leaded lights, but in artistic value it is rather inferior.

Rippled is a rolled glass with a very strong surface marking somewhat like muffled, but too pronounced and rather toe regular to be altogether pleasant. It may be looked upon as a sort of imitation of muffled,

Figured Rolled is produced by means of a machine having rollers with engraved surfaces which impress their pattern upon the surface of the glass. The artistic value of these patterns is practically nil. The glass is used principally in large sheets for screens where diffusion of light without transparency is required, and though it occasionally finds its way into the cheaper class of leaded lights, the effect is almost invariably as bad as it can be. In large sheets, on the other hand, the effect of the patterns, which vary con¬ siderably in size, is brilliant and, on account of their power of diffusing light, frequently very useful. White and some dozen light tints are to be had.

Flemish is another variety of rolled glass somewhat similar in character to Double Rolled, but having a much larger “ wave,” and very much heavier in body. It is made in white and tints, and its peculiar character of surface makes it extremely useful in leaded lights where a brilliant effect is required in a window much overshadowed by other buildings, muffled glass being also advantageous in such a position. Against a clear sky it loses almost all its effect and becomes no better than ordinary rolled. It should be noted that all the glasses with roughened or wavy surfaces come into this category and do not show to advantage unless viewed against a comparatively dark background with the light falling upon them at a more or less acute angle.

Crapene is a recent introduction very similar to Flemish, but more mechanical in its marking and therefore not quite so good in effect.

Variegated and Opalescent Rolled glasses are valuable on account of the very great variety of broken colour which they afford, and which at times places them, for certain purposes at least, almost on a level with the most expensive Antiques. Variegated Rolled was first made in England some twenty years ago, but did not “ catch on.” Since then it has been revived and Opalescent Rolled introduced by American enterprise, and both have been extensively used in the recent “ boom ” of leaded light work. They are both made with “ rippled ” as well as “ rolled ” surfaces, the “ rippled ” having a peculiar glitter which is very useful under certain conditions and in small pieces. These glasses, as a class, are very bad for cutting, as they are badly annealed. The pressure of the diamond is quite sufficient to smash a large sheet, and the unequal and sometimes “ thready ” surface is apt to make the cut a very unsteady one. They cut very well under the wheel, however, and it is generally found best to use it alone on glass of this nature. The opalescent has rather a bad fault in that the milkiness produced by the tin oxide which enters largely into the colouring matter of the glass is glaringly visible from the outside, but this defect can be turned into an advantage where ornament, and especially lettering, is required to show to the outside, as in the case of sign¬ boards, door panels, etc. Moreover, it will not stand firing, the milkiness becoming much more turbid and dense during the process. Variegated glasses change colour in the kiln, generally becoming much darker. There is also a very great risk of breakage, both with opalescent and variegated, the imperfect annealing making them specially subject to “fire cracks.” When it is necessary or desirable to use these glasses for painted work it is usual to “ plate ” them with clear sheet, the painting being done upon the sheet

KINDS OF GrLASS glass. Their chief value, however, is for leaded light work, where their beautiful broken colour lends itself specially to combination with light backgrounds and varying thick¬ nesses of lead.

One of the most beautiful of the opalescent glasses is Opalescent Reamy Sheet. The opal is flashed upon one side in irregular streaks and splashes and is nowhere solid white. It is only made in white. Being a flashed glass it is open to treatment with acid. It has been used with great success for lettering on doors for restaurants, etc., by aciding away the background and leaving the letters white. The result is particularly happy in producing a letter which is varied in quality and perfectly legible without showing the staring, chalky effect generally inseparable from opal glass. A veiy lich eflect can also be produced by embossing clear ornament upon an opal ground. This glass is worthy of being better known and more widely used, as its capabilities are by no means exhausted by the uses suggested above.

Under the heading of Antiques we find a great variety of most useful glasses — Pot, Flashed, Streaky, and Venetian. Pot metal glass is that in which the colouring material is mixed thoroughly with the other ingredients during the piocess of melting the glass is coloured right through, and the only variation which can be obtained is a slight shading from light to dark owing to the varying thickness of the glass, which may range from inch to \ inch within a square foot. Plashed glass, on the other hand, is not coloured right through, but has merely a very thin film of colon i laid upon one side of a sheet of white, pale green, yellow, or pale blue. The practice probably arose from the great power of the colouring materials used to produce ruby

— pot metal ruby (!) would be positively black — but it has developed other advantages, as, for instance, the possibility of removing or modifying the “ flash ” by means of hydro¬ fluoric acid, and also of modifying the colour by flashing it upon differently-coloured bases. Ruby is the colour most frequently produced in this way, but blue is also to be had, and occasionally green. At one time the number of colours made in flashed glass was much greater than it is now. Purples and yellows were to be had, but of course the value of the latter was largely diminished by the fact that a very similar effect could be more conveniently produced on white glass by means of stain. Streaky glasses are made by dipping the blowpipe successively into pots of differently coloured “ metal ” and working the small quantities thus collected into one mass, the different colours remaining more or less distinct in hue, but being distributed in streaks across the surface. Greens, whites, and yellows are the colours most frequently treated in this way and are extremely useful for high-class work. Streaky antique has the disadvantage which has already been mentioned in connection with variegated rolled— it is very apt to change colour in the kiln and even to break, though in this latter respect it is much safer than variegated rolled. It is also apt to show a number of minute cracks known as “ crissles,” any of which may, during cutting or afterwards, develop into a break. Venetian glass is made by blowing a “ bubble ” of glass into a cylindrical iron mould having a strongly-marked screw pattern on its interior surface. It is then removed to another mould with a reversed, or lefthanded, screw pattern. Between the two is produced a lozenge pattern which loses some of its definition and regularity in the subsequent stretching of the bubble to a full-sized “ muff.” It is a very brilliant glass, but on account of the strongly-marked pattern it is not very suitable for use in large pieces. Cut up into small pieces its brilliant lozenges make admirable “jewels” for orna¬ mental leaded lights. The range of colour is confined to light tints and opalescents.

Antique glasses are all made by blowing in cylinders or “ muffs ” which are afterwards split and flattened out in a kiln into sheets of about 24 inches by 16 inches. The range of colour is practically unlimited. “ Whites ” include pure whites, “warm” whites, “streaky” whites, and “ dark ” whites, which might be called light greens. Ruby is flashed upon white, warm white, green white, yellow, and blue. Blue is flashed upon pure white and greenish white. Pot metal colours range through yellows, greens, blues, purples, browns, pinks, etc., and from light to dark, in a bewildering variety. Sometimes thick edges of sheets become so dark as to transmit no light at all. Antique glasses, except perhaps streaky, which is sometimes trouble¬ some if not well annealed, cut well under either diamond or wheel, and stand firing well, except that some of the softer metals, greens particularly, come rather near melting point and are apt to lose their brilliance and sparkle. Neutral colours, too, are sometimes apt to change colour, becoming darker. Antique whites take silver stain very readily, but those which are greenish in hue are rather apt to show the stain on the outside as an opaque-looking yellow smudge. Antique glass is the main stock-in-trade of the painter of memorial windows, to whom its range and richness of colour and the ease with which it can be cut, painted, and fired are invaluable. One frequently hears complaints that the art of glass-making has been lost, and that no modern glass can compare with the glass of the old windows, but, as a matter of fact, the case stands entirely the other way. A hundred years ago such statements were doubtless true enough, but the state of affairs has entirely changed since then, and the modern glass painter has a variety of glass and a quality of glass that might well make the old monks and their co-workers turn in their graves with envy. There is certainly some fine glass in the thirteenth and fourteenth century windows at Canterbury, York, and elsewhere, but there is none that cannot be equalled and surpassed by the modern glass-maker. Apart from the mellowing effects of time, the richness of a great deal of old glass is entirely dependent on the fearless way in which strong colours such as ruby, blue, and green are thrown together, generally in small pieces, and wherever that system is adopted in modern work the effect is at least as good.

Perhaps the finest colours in Antique glass are those obtained by flashing Gold Pink upon white, yellow, blue, and purple. The colouring matter in this case is actually gold, which supplies an economic reason for flashing the glass instead of making pot metal, and the pink produced upon white glass is of a very beautiful quality. Flashing it upon a yellow base brings it to something like a scarlet, upon blue produces a fine violet, and upon purple a rich colour unapproachable by any other means. Gold Pink is also made in opalescent and streaky forms, which are generally more useful for jewel-like bits in good leaded lights than for memorial window work. Somewhat similar to Antique in richness and quality of colour — the metal is the same — but possessing a peculiar quality of its own to which words would do scant justice, are Norman Slab or Bottle glass and Wood White bottle glass. These are pro¬ duced by blowing a bubble of glass into an iron box-shaped mould. Where the soft metal first touches the mould it will be perhaps half an inch thick, but as it gradually ~ expands into the corners it quickly thins away and occasion¬ ally bursts in the extreme angles. When turned out of the mould it looks like a glorified pickle bottle or Leclanche electric cell — split up the corners, it produces four slabs of glass about 7 inches by 5 inches, and one 5 inches by 5 inches. These show a fairly dark spot of colour in the centre where the metal is thickest, growing lighter towards the edges as it grows thinner. There is a peculiar watery quality about this glass which cannot be found in any other and is specially valuable in leaded light work for domestic purposes. For ecclesiastical work the brilliant depth and translucent jewel-like quality of the colour add very great richness to any colour scheme. Streaky opalescent and gold pink are all to be had in this form, while the range of colour is practically equal to that of antique. Wood White is a very pure silvery white glass made in the same way,' of about the same size and also smaller — about 5 inches by 3i| inches — and is frequently used in its original size for plain square leaded lights where a quaint, colourless effect is required.

Of a similar nature to the above are Pressed Slabs. They are made from the same metal as Antique and Norman, but shaped into pieces about 8 inches by 8 inches, and smaller, by stamping. It is very similar in quality to Norman, and

Eig. 2. — Designs for Leaded Lights, by A. L. Duthie.

KINDS OP GLASS is produced in a large variety of colours, including many fine streaky and variegated effects.

Amongst other “ fancy ” glasses of a similar nature may be mentioned “Luna ” glass. This is a muff glass, similar to Antique, with a peculiar iridescent surface. Over the body of the metal are laid a number of streaks which look as they might have been produced by a very soft enamel poured on in little streams which cross and recross in every direction. Owing to its iridescence it would be most useful in domestic and furniture work.

Anbitty is a very fine glass of a “ sheet ” nature varying from an almost transparent surface to a surface as obscure as muffled. It is made in light tints, some of which become strong enough to be called greens. The lighter tints stain very well, and the peculiar quality of surface is emi¬ nently suitable for high-class painted and stained work of Renaissance or semi-natural design. Anbitty is produced by keeping the molten metal at a certain temperature for some hours before blowing. Under these conditions the glass tends to crystallise, and the peculiar texture is due to the presence of numerous minute crystals in the body of the sheet.

Fluted sheet, though hopelessly crude and mechanical in large surfaces, is very useful in small pieces and narrow “ lines” in leaded lights.

Tinted or Cathedral sheet is not so much used now as it was some years ago, having been ousted by the cheaper rolled. It has rather a quaint effect, because though tinted it is still almost as transparent as clear sheet. It is useful for church and chapel windows as well as for domestic work.

The bull's-eyes which formed the centres of sheets of crown glass have had such a vogue for leaded lights that they have even been taken out of old windows in cottages, farmhouses, workshops, and stables to supply the demand for them. They are now specially manufactured for leaded light work. Somewhat resembling them, but circular in form and having a very much smaller and thinner “eye,” are roundels, which have always been largely used in leaded lights and are characteristic of German and Italian win¬ dows. They are made in an infinite variety of colour and size, but require to be very carefully handled with regard to design to prevent their looking commonplace. White roundels painted with suitable patterns and stained gain considerably in interest. In addition to roundels there are also to be had a great variety of stamped patera and facetted j excels, the majority of which cannot be recommended for use in good- class work, though the plainer of them can frequently be turned to very good account by a smart designer. Some further remarks on the use of the fore¬ going glasses will be found under the heading of Design in Chapter II.

Opal glass, useful for lettering, advertising devices, etc., on account of its opaque white surface, is made both as pot metal and flashed, the latter being, of course, capable of being treated with acid, giving white lettering or orna¬ ment on a clear ground, or vice versa. It is also possible to obtain pot opal glass flashed with turquoise, yellow, orange, and ruby, which can be treated with acid, removing the coloured veneer and exposing the white base as may be required.

Herewith is given an approximate price list of the various glasses mentioned above, which is intended to give an idea of the relative value as a guide to the freedom with which they can be used as regards economy. Some of them vary slightly from time to time owing to market fluctuations, but the following will be sufficiently accurate as a guide to relative value.

COMPARATIVE LIST OF GLASS PRICES.

Subject to Market Fluctuations.

Per sc

. ft.

Per so. ft.

Sheet glass —

S.

d.

s.

d.

Antique streaky n

Venetian white .

4*

, , pot metal .

Patent plate

, , streaky

Crown .

,, opalescent .

Rough cast plate

Norman slabs (according to

Patent rolled plate .

size) 2s. 6d. to 21s. per

Polished plate .

doz.

Rolled Cathedral

Wood white (according to

Double rolled Cathedral .

size) 2.s. 6d. to 15s. per

Muffled .

doz.

Rippled .

Pressed slabs, from 12s. per

Figured rolled .

doz. upwards.

Flemish .

Luna ....

Crapene .

Anbitty ....

Variegated and Opal¬

Fluted sheet escent rolled .

Cathedral sheet .

Opalescent reamy .

Bull’s - eyes (according to

Antique whites size) 4s. to 48s. per doz.

,, pot metals .

Opal — -

,, rubys

Pot metal .

,, gold pink .

Flashed

Chapter II

The practice of joining together small pieces of glass by means of bands of lead probably had its origin in the Middle Ages in the fact that it was only possible then to make glass in small pieces which would have to be joined together to make up the size necessary for the glazing of windows. The opportunity thus given for the introduction of differently coloured glasses was, of course, quickly recog¬ nised and paved the way for the development of stained glass windows, but at the same time for both ecclesiastical and domestic work the use of leaded patterns in clear and light tinted glass continued, and many fine geometrical patterns of mediaeval origin are to be found both in this country and abroad. The interest added to a window by a leaded pattern is unquestionable. The use of lead work lapsed almost entirely during the Renaissance period, but since then it has revived and at the present time is being used in buildings of all styles. The process in itself, how¬ ever, is still the same as was employed by the mediaeval craftsman. The diamond and the wheel have replaced the red-hot iron for cutting, and hydraulic-drawn lead has ousted cast lead, but otherwise the work goes on as before. It is essentially a handicraft. The first step is the making of a full-sized drawing showing the size of each piece of glass, the lines upon it representing the heart of the lead.