Glassblower

“ Fun blowing glass bubbles. Smooth one end of a piece of No. 2 tube and allow it to cool. Close the other end in the blowpipe flame, turn it slowly, and heat until it is very hot. Take the tube out of the flame, put the smooth end into your mouth quickly, and blow as hard as you can (Fig. 11) . Do you get a fine big glass bubble which bursts with a pop?
7If you get only a small bulb at the first trial, heat the end, and try again. Do you find that the bulb shrinks when heated but blows out again readily? ”

“ The habit of constant and instinctive rotation is literally about one-third of the whole art of glassblowing. It is unlikely, however, that the beginner will discover that he has not got this habit, until a few failures draw his attention to it.
The glass tube being held in position lightly yet firmly, and the operator being sure that he feels comfortable and at his ease, and that the blow-pipe flame (a single flame in this instance) is well under control, the preliminary heating may be commenced. ”

“ While occupied in rendering popular, if we may so speak, the use of the blowpipe—an instrument which is so advantageous in a great number of circumstances—we have also endeavoured to improve the lamp, which has, until the present time, been used by all those who employ the glass-blower’s table. ”

“ From the infinite diversity of objects into which glass is thus moulded, it must be obvious that the operations of these artificers embrace a variety of curious details which it is impossible to enter upon here; but a glance at some of them will enable the reader to form a general notion of the curious manipulations upon which they are so actively employed.
The initial movement of the glass-blower is to dip a hollow iron rod or tube, about five feet long, through the bocca, into one of the crucibles containing the melted glass. ”

“ The word glass-blower, generally speaking, signifies a workman who occupies himself in making of glass and enamel, the instruments, vessels, and ornaments, which are fabricated on a larger scale in the glass-houses: but the domain of the sciences having laid the art of glass-blowing under contribution, the artists of the lamp have divided the labours thereof. Some apply themselves particularly to the construction of philosophical and chemical instruments; others occupy themselves with little ornamental objects, such as flowers, &c. ”

“ Such a bellows may be obtained at almost any jewellers' supply dealer in Clerkenwell, but it not infrequently happens that the spring in the wind [Pg 6] chamber is too strong for glass-blowing, and hence the air supply tends to vary in pressure. This can be improved by fitting a weaker spring, but an easier way and one that usually gives fairly satisfactory results, is to place an ordinary screw-clip on the rubber tube leading from the bellows to the blowpipe, and to tighten this until an even blast is obtained. ”

“ Many laboratories in this country, especially in the west, are located a long way from any professional glass-blower, and the time and money spent in shipping broken apparatus several hundred miles to be mended could often be saved if some of the laboratory force could seal on a new stopcock, replace a broken tube, or make some temporary repairs. Many men in physical or chemical laboratories have occasion to modify some piece of apparatus designed perhaps for other uses, or to design new apparatus. ”

“ Fortunate indeed is the boy who receives a stock of glass tubing, a Bunsen burner, a blowpipe, and some charcoal for a gift, for he has a great deal of fun in store for himself. Glass blowing is a useful art to understand, if the study of either chemistry or physics is to be taken up, because much apparatus can be made at home. And for itself alone, the forming of glass into various shapes has not only a good deal of pleasure in it, but it trains the hands and the eye. ”

“ In the case of a blowpipe burning oil or wax fuel the flame may be a trifle more ragged without disadvantage.
Bellows and Blowing.—The bellows should be adjusted to deliver air at constant pressure, either by insertion of a tap or, better, by attention to the wind reservoir if necessary. The movement of the foot in blowing should be steady, not jerky.
Heating Glass.—The tube or rod should be heated cautiously until it has reached its softening point in its thickest part. Steady rotation of the glass during the heating is almost essential. ”

“ The advantage which it possesses over crown glass is, that much larger sheets can be made, and this is very easily noticed if we examine the larger dimensions of common window panes compared with those which were formerly made. Even now the workmen employed in this class of manufacture are generally Belgians. A sheet glass blower must be very strong, and have great skill in handling his blowpipe, for the cylinders which he blows are frequently sixty inches long, and their weight is very considerable. Glass shades are blown by sheet blowers. ”

“ Jets of several sizes to fit the air-tubes of blow-pipes may be obtained with them, and will serve for regulating the supply of air to the flame.
The Bellows.—The usual blowing apparatus is some form of foot-blower. These may be obtained fitted to small tables with sheet-iron tops. But a much less expensive apparatus is the large foot-blower made by Mr. Fletcher of Warrington, which can be used at an ordinary table or laboratory bench. Good foot-blowers can also be obtained from makers of furnace bellows.
Fig. 2
No part of the glass-blower’s equipment exceeds the bellows in importance. ”

“ In holding a tube for breaking, it is important to place the hands as shown in sketch, as this method is least likely to cause shattering and also minimises the risk of injury even if the tube should shatter. To cut a large tube, or one having very thick walls, it is better to avoid straining altogether and to break by applying a small bead of intensely heated glass to the file cut. If the walls are very thin, a glass-blower's knife should be used instead of a file. The tube and glass-blower's knife should be held in the hand, and the tube rotated against the edge of the knife ”

“ In the production of hollow glass-ware by hand, the glass-blower avails himself to the full of the property so characteristic of glass of assuming a pasty or viscous condition when suitably heated; by raising or lowering the temperature of his material, the blower can at will render it stiffer or more fluid; by blowing he can distend it, draw it out by the aid of gravity or centrifugal action, or he can mould it with the aid of rods and tongs of suitable shape, while at times he allows it to fall or festoon under its own weight while held aloft. ”

“ The flame of a lamp, or candle, condensed and directed by a current of air, is exceedingly useful in a great number of arts. The instrument which is employed to modify flame is the Blowpipe. This is an indispensable agent for jewellers, watch-makers, enamellers, glass-blowers, natural philosophers, chemists, mineralogists, and, indeed, for all persons who are occupied with the sciences, or their application to the arts. Its employment offers immense advantages in a multitude of circumstances ”

“ I have now to speak of another class of moulded glass, of what is, in fact, a true ‘hollow ware,’ made by 57 blowing a vesicle of glass into a mould. This is the first time that we unmistakably come across the use of the blowing-tube. In the case of glass it is practically impossible to use a mould in the shaping of a hollow vessel without some such method of forcing the viscid material into its place by pressure from the inside. ”

“ In very much of his work the glass-blower is guided more by the feel of the glass than by what he sees. The power of feeling glass can only be acquired by practice, and after a certain amount of preliminary failure. ”

“ Simple bulbs and joints do not even need this smoking; but thick articles, and especially those that are to be subjected to the stress of grinding, need more prolonged annealing in a special oven.
Use of Lead-Glass.—When lead-glass is to be used, the blowpipe flame should be in good adjustment and the glass should not be allowed to approach so near to the blue cone as to be blackened. Slight blackening may often be removed by heating the glass in the extreme end of the flame.
Lead-glass articles tend to be rather more stable than similar articles of soda-glass. ”

“ Many glass-blowers habitually employ an agate, or a common flint, which they hold in one hand, while with the other they rub the tube over the sharp edge of the stone, taking the precaution of securing the tube by the help of the thumb. For tubes of a greater diameter, you can employ a fine iron wire stretched in a bow, or, still better, the glass-cutters’ wheel ”

“ A full account of the process of blowing crown-glass will be found in all older books and articles on the subject, so that it need only be mentioned here that the glass, instead of being blown into a cylinder, is blown into a flattened sphere, which is caused to burst at the point opposite the pipe and is then, by the rapid spinning of the glass in front of a very hot furnace-opening, caused to expand into a flat disk of large diameter. ”

“ From two to five minutes, heating at a distance of about eight inches in front of the flame will be found sufficient in most cases, and another minute should be taken in bringing the tube into the flame. Gradual heating is important, but even heating is still more important and this can only be obtained by uniform and steady rotation. Until the student can rotate a tube steadily without thinking about it, real progress in glass-blowing is impossible. ”

“ My own blow-pipe is placed near a window glazed with opaque glass, which looks southwards, but is faced by buildings at a short distance. In dull weather the light obtained is good; but on most days I find it advantageous to shade the lower half of the window with a green baize screen. Some glass-blowers prefer gaslight to daylight. ”

“ There is a wide choice of apparatus, from a simple mouth-blowpipe and a candle flame to a power-driven blower and a multiple-jet heating device. All are useful, and all have their special applications, but, for the present, we will consider the ordinary types of bellows and blowpipes, such as one usually finds in a chemical or physical laboratory.
The usual, or Herepath, type of gas blowpipe consists of an outer tube through which coal gas can be passed and an inner tube through which a stream of air may be blown. Such a blowpipe is shown in section by Fig. ”

“ Allusion has been made (page 2) to the Roman practice of making glass in strata of two colours, which they carved cameo-fashion in imitation of onyx and the like; at least, one tour de force of this kind is familiar to every one in the famous Portland vase, in which the outer layer of white glass is in great part ground away, leaving the design in cameo upon dark blue. The mediæval glass-blower seems from the first to have been acquainted with this method of coating a sheet of glass with glass of a different colour. ”

“ Finally, in Chapter V., there is a short account of the methods of graduating and calibrating glass apparatus for use in quantitative experiments.
The Working-place.—The blow-pipe must be placed in a position perfectly free from draughts. It should not face [3] a window, nor be in too strong a light, if that can be avoided, for a strong light will render the non-luminous flames, which are used in glass-blowing, almost invisible, and seriously inconvenience the operator, who cannot apply the various parts of the flames to his glass with the degree of certainty that is necessary ”

“ The ordinary soda-glass tubing melts easily in the blowpipe flame, it has not a long intermediate or viscous stage during fusion, but becomes highly fluid rather suddenly; it does not blacken in the reducing flame. Bad soda-glass or that which has been kept for many years, tends to devitrify when worked. That is to say the glass becomes more or less crystalline and infusible while it is in the flame ”

“ There is no need, however, to purchase an expensive table for laboratory use. All the work described in this book can quite well be done with a simple foot bellows and a quick-change blowpipe. Nearly all of it can be done with a single jet blowpipe, such as that described [Pg 7] first, or even with the still simpler apparatus mentioned on page 84, but I do not advise the beginner to practise with quite so simple a form at first, and for that reason have postponed a description of it until the last chapter. ”

“ The use of such a blowing-tube avoids the inconvenience of raising the work to the mouth when internal air-pressure is required. One end of the rubber tube is retained in the mouth during work.
General Notes.—A large amount of glass-blowing is spoiled through carelessness in arranging the work beforehand. The student should have every detail of his manipulation clearly in mind before he commences the work; [Pg 103] he should not trust to evolving the method during the actual manipulation. ”

“ A modern glass-blower, when making an amphora-shaped vase, finishes the base first, fixes an iron rod to the finished base with a seal of glass, severs the vase from the blowing iron, and finishes the mouth, whilst he holds the vase by the iron attached to its base. ”

“ This puts both hands in a position where the tube may be blown and rotated uniformly while its axis is kept horizontal.
Smoothness and exactness are the two things for which the beginner must constantly strive in glass-blowing, and they are only attained by a careful attention to the details of manipulation, with a steady hand and watchful eye. Every move must count, and the exercise must be finished with a minimum of reheating and retouching, for the best results. ”