Glass rod

“ During the process of manipulation, whether on the chair or whilst the glass is being reheated, the rod must be constantly and gently trundled to prevent the collapse of the bulb or vessel. Every natural development of the spherical form can be obtained by blowing and fashioning by hand. A non-spherical form can only be produced by blowing the hollow bulb into a mould of the required shape. Moulds are used both for giving shape to vessels and also for impressing patterns on their surface. ”

“ When the kind of glass called “crown-glass” has to be made, the end of the iron tube is put into the pot of melted glass, and turned round till a ball of it is collected about the size of one’s head, the workman then blows in at the other end, still turning the rod in his hands; it has now the appearance presented at fig. 3. An iron rod is stuck on to the side of the globe opposite to the “puntil,” which is then pulled suddenly away, leaving a round hole. The globe of glass is again made red-hot, and spun round rapidly, the hole increasing in size until it resembles fig. ”

“ The rod with the globe attached to it is now held at the mouth of a glowing furnace: and by turning the rod the globe is made to revolve slowly, so as to be uniformly exposed to the heat: the first effect of this softening is to make the glass contract upon itself and to enlarge the opening of the neck. ”

“ The glass must now be ground with coarse emery upon its appropriate mould, whether convex or concave, the emery being all the time kept moist with water. To prevent the heat of the hand from affecting the glass, a rod for holding the brass plate is screwed to its back. For every six turns of circular motion, it must receive two or three rubs across the diameter in different directions, and so on alternately. The middle point of the glass must never pass beyond the edge of the mould; nor should strong pressure be at any time applied. ”

“ Larger Holes in Glass.—The method of drilling with a hard steel rod is not highly satisfactory for anything but small holes. When a larger hole, say one of an eighth of an inch or more, is needed it is better to use a copper or brass tube. This tube may be held in an American hand-drill, but a mixture of carborundum or emery and water is supplied to the rotating end. Tube or drill must be lifted at frequent intervals in order to allow a fresh supply of the grinding material to reach the end. ”

“ The first point of importance in considering the stem is to distinguish those that are drawn—these are the ‘straw-shanks,’ formed of the same piece of metal as the bowl—from the ‘stuck-shanks’ that are made of a separate piece of glass. The latter form by far the larger class. As regards the outline, the stem may be either a plain rod or cylinder, or again of baluster shape—this last but a modification of the double knops that constitute the whole shank of some seventeenth-century glasses. ”

“ The effect of great velocity in modifying the form of a cohesive substance is beautifully shown in the process for making window-glass, termed "flashing," which is one of the most striking operations in our domestic arts. A workman having dipped his iron tube into the glass pot, and loaded it with several pounds of the melted "metal," blows out a large globe, which is connected with his rod by a short thick hollow neck. Another workman now fixes to the globe immediately opposite to its neck, an iron rod, the extremity of which has been dipped in the melted glass ”

“ When the glass is softened it sinks of itself, in consequence of the rotatory motion given to it, towards the axis of the tube, and becomes rounded. The application of no instrument is necessary.
If the tube is of considerable diameter, or if the sides are thick, you must soften the end, and then, with a metallic rod or a flat pair of pliers, mould the sides to a hemisphere, by bringing the circumference towards the centre, and continuing to turn the tube in the flame, until the extremity is well sealed, and perfectly round. ”

“ 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. ”

“ This tube, broken into rods of convenient lengths, then passes into the hands of another set of workmen, living for the most part in Venice. The rods are now carefully sorted, as to size, by women—the cernatrici—and handed over to the cutter, who, seated at a bench, cuts off equal lengths by passing the rod between a blade or chisel held in the hand, and a similar tool fixed in the bench, the size of the fragments being regulated by means of the scontro, a semi-cylindrical block of steel. ”

“ As a rule, soda-glass will need more annealing than lead-glass.
Drilling Glass.—Small holes may be drilled in glass by means of a rod of hard steel which has been broken off, thus giving a more or less irregular and crystalline end.
There are several conditions necessary to enable the drilling of small holes to be carried out successfully:—the first of these is that the "drill" should be driven at a high speed. ”

“ The globular mass formed by the first blowings is held by a workman vertically over his head. An assistant gathers a small quantity of soft glass from the furnace on the end of a pointed iron rod, and causes it to adhere to the flattened surface, at a point opposite to that to which the blowpipe is attached. The glass near the blowpipe, while hot, is touched with a cold instrument, and immediately cracks around its neck, detaching the blowpipe from the mass. ”

“ Having severed the body of the vase from the blowing iron, he heated and closed the fractured base, whilst holding the vase by means of the rod fixed in the neck. Nearly every specimen shows traces of the pressure of a tool on the outside of the neck, as well as signs of the base having been closed by melting. Occasionally a knob or excrescence, formed by the residue of the glass beyond the point at which the base has been pinched together, remains as a silent witness of the process. ”

“ You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space. ”

“ These operations, particularly when weights of thirty or forty pounds of glass have to be gathered, require the exercise of a great deal of skill and care; the introduction of the gathering into the molten glass is each time liable to produce air-bells which would spoil the whole mass of89 glass or would contaminate the contents of the crucible, while subsequently the mass of hot glass adhering to the rod or pipe tends to run down and even to drop off entirely if not properly checked by suitable rotation of the pipe. ”

“ If an open-mouthed vessel is to be made, an iron rod, called a ‘pontil’ or ‘puntil,’ is dipped into the glass-pot and applied to the bottom of the flask, to which it thus serves as a handle, the blow-pipe being removed by the application of a cold iron to the neck. ”

“ The trout very naturally spawn in the upper waters, but return to live and sport about the feeding-grounds of the lower ponds, where there are excellent contrivances for affording them shelter; and as the water is very clear, the habits of the fish can be noted with great ease. The family seems to be most despotically governed, a few of the larger trout ruling the others with a rod of iron ”

“ These sometimes are very large, and require great skill. When their shape is to be that of a cylinder with a dome top, they are made as in the ordinary course of blowing a cylinder of sheet glass, but instead of one end being burst as described, they are simply detached from the blowpipe. When they have to be oval or square at their bases, they are blown into wooden moulds of the required form, which have their insides charred. The gathered mass of glass is placed inside such a mould, and is then blown into until it touches the sides. ”

“ Glass beads are utterly unnecessary, and there is no design or thought employed in their manufacture. They are formed by first drawing out the glass into rods; these rods are chopped up into fragments of the size of beads by the human hand, and the fragments are then rounded in the furnace. The men who chop up the rods sit at their work all day, their hands vibrating with a perpetual and exquisitely timed palsy, and the beads dropping beneath their vibration like hail. ”

“ In the centre of the floor stands the revolving machinery enclosed in a heavy metal case, upon which the huge lens, with its supporting carriage, revolves. The lens itself—a marvel of the glassmaker’s art—is the production of a French firm. Imagine a huge saucer, twelve feet in diameter, composed of twenty concentric prisms of purest glass, each with a diameter almost as much as a man may enclose with both hands, terminating centrally in a sixteen inch plano-convex lens or bull’s-eye. ”

“ Gilding and enamel decoration are applied to vessels when cold, and fixed by heat.
Cutting and engraving are mechanical processes for producing decorative effects by abrading the surface of the glass when cold. The abrasion is effected by pressing the glass against the edge of wheels, or disks, of hard material revolving on horizontal spindles. The spindles of cutting wheels are driven by steam or electric power. The wheels for making deep cuts are made of iron, and are fed with sand and water. ”

“ The final stage with which we are concerned is that of blowing, since all table glass, worthy of being called table glass, is blown. In other words, every decanter, vase, tumbler, and wine glass of the better sort begins its existence as a bubble of molten glass at the end of an iron tube—the glass-blower’s tube—and owes its form to the delicate touches of simple tools held in a skilful hand and guided by a trained eye. It is this fact which gives glass its individuality. There is no hard-and-fast rigour of line, no mechanical uniformity of shape, such as is associated with machine-made goods ”

“ When it is desired to cut a design on the outside of a tumbler or wine-glass, the vessel is, in the first instance, blown of a thicker substance than if it is to be left uncut. The necessary shapes, which are usually in facets, are cut upon it by the action of sand and water, a lathe of a very simple construction being used to give a rotary motion to cutting discs, made of stone and kept continually moist by water dripping on them, so that when the glass is pressed against them, the required portion of its surface is worn away. ”

“ There is some reason to believe that when the use of the blowing-tube was first introduced it was applied as a supplement to a moulding process. The hollow vesicle of glass—the paraison, to use the old French word—was blown into a more or less hemispherical mould, and the irregularities of the resulting bowl were then removed by grinding on a wheel. At any rate, during what we may call the Alexandrian period, a bowl of simple outline, whether shallow or deep, is the characteristic form. In the case of certain dishes in the shape of a boat, the wheel has played a still more important part. ”

“ It has been found that it is quite impossible to prevent these irregularities, which appear to arise from the buckling of the glass against the iron surfaces with which it comes into contact; when rolled, the glass is too stiff to recover its true, smooth surface under the influence of surface tension, so that it retains all the marks of roller and table—nor can the roller be made perfectly smooth, since in that case it appears to slip over the glass and does not roll it out properly. ”

“ 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 ”

“ Each of these men has a work-hole of the furnace to himself, so that he may heat his material any time he needs to do so. The staging gives him room to swing his heavy mass of glass as he blows it, and the pit in the floor, which is about ten feet deep, furnishes space for the big cylinder to run out, or grow longer, as he blows. The gathering for sheet glass is done much as was that for the smaller pieces. The gatherer collects a lump on his pipe, cools it a little, and collects more until he has enough. ”

“ Surely so much information has rarely been compressed into one print as we find in the main illustration to this part of Agricola’s text (Plate XXXVIII.) . Here at one working-hole (fenestrella) we see a workman gathering the glass at the end of his fistula or blowing-iron, another is shaping the gathering upon the marver at his foot, a third is vigorously blowing the paraison to the required size, and a fourth is swinging another round his head. On the ground lie scattered moulds of various forms, and here, too, we may discover the forceps (pucella) used in shaping the glass. ”