W. A. Shenstone

“ Many amateurs find that soda glass is in some respects easier to work with than lead glass. But, on the other hand, it is somewhat more apt to crack during cooling, which causes much loss of time and disappointment. Also, perhaps in consequence of its lower conductivity for heat, it very often breaks under sudden changes of temperature during work. If, however, a supply of good soda glass is obtained, and the directions given in this book in regard to annealing it are thoroughly carried out, these objections to the use of soda glass will, to a great extent, be removed. ”

“ 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. ”

“ The excellence of a burner does not depend on the size of its flame, so much as on the temperature of its “hot spot,” and the success of the worker depends on his skill in bringing his work exactly to this part of the flame. Comparatively large masses of silica may be softened in a comparatively small jet if the hot spot is properly utilised. ”

“ For a long spell of labour at work which is not of a novel character nor specially difficult, I am disposed to recommend sitting on a chair or low stool, at a table of such height as will enable the elbows to rest easily upon it whilst the glass is held in the flame. ”

“ It is easier to blow large bulbs on large-sized tubes than on those of smaller size. When it is necessary to make a large globe on a small tube, it can be done, however, if great care be taken to avoid overheating that part of the small tube which is nearest to the mass of viscous glass from which the bulb is to be formed. For the purpose of blowing a very large bulb on a small tube, it is best to unite a wide tube to that which is to serve as the neck, as it will save some time in collecting the necessary mass of glass from which to form the globe. ”

“ As a consequence of this, it is in one respect much more easily worked in the flame than any form of glass. Difficult joints can be thrust suddenly into the flame, or removed from it, at any stage, and they may be heated unequally in different parts with impunity. It is safe to say that joints, etc., in silica never crack whilst one is making them nor during the subsequent cooling. They may be set aside in an unfinished state and taken up again without any precautions. Therefore it is possible for an amateur to construct apparatus in silica which he would be quite unable to produce from glass. ”

“ The individual operations of glass-blowing are much less difficult than is usually supposed, and considerable success in the performance of most of them may be attained by any one who is endowed with average powers of manipulation and who is moderately persistent. Constructing finished apparatus is often more difficult, as it may involve the performance of several operations under disadvantageous conditions, and may demand a little ingenuity on the part of the operator. ”

“ If at any time the glass shows indications of collapsing, it must be removed from the flame and gently blown into shape, during which operation it may be rotated in the perpendicular position; indeed, to promote a regular distribution of the glass by allowing it plenty of time to collect, it is well from time to time to remove the heated mass of glass from the flame, and slightly expand it by blowing. ”

“ If a platinum wire embedded in a thick silica tube be heated from without by an oxy-hydrogen flame the metal may be melted at temperatures at which the silica tube will retain its form for a moderate length of time, but silica softens to a marked extent at temperatures a little above the melting point of platinum.
It has been observed by Boys, Callendar, and others that fine rods of silica, and also the so-called “quartz fibres,” are apt to become brittle after they have been heated to redness. ”

“ When it is only required to bend or draw out tubes of lead glass, they may be softened sufficiently by a smoky flame, which, probably owing to its having a comparatively low temperature, does not so readily reduce the lead as flames of higher temperature. But for making joints, collecting masses of glass for making bulbs, and in all cases where it is required that the glass shall be thoroughly softened, the smoky flame does not give good results. ”

“ The tube to be heated should be held in the position shown in Fig. 6, supported by the hands on each side. It should be constantly rotated in the flame, that it may be equally heated on all sides. In the figure the hands are represented above the tube, with their backs upwards. A tube can be held equally well from below, the backs of the hands being then directed downwards, and this, I think, is the more frequent habit. It is difficult to say which position of the hands is to be preferred. I lately observed how a tube was held by three skilful amateurs and by a professional glass-blower. ”

“ To Produce an Oxidising Brush Flame.—The blower used must be powerful, the air-tube of the blow-pipe must be about half as great in diameter as the outer tube which supplies the gas. The operator must work his bellows so as to supply a strong and steady blast of air, and the supply of gas must be regulated so that the brush flame produced is free from every sign of incomplete combustion, [5] which may be known by its outer zone being only faintly visible in daylight, and quite free from luminous streaks (see Fig. 4, p. 9) . ”

“ As a rule I have observed that beginners are apt to raise their glass to a higher temperature than is necessary, and that they employ larger [23] flames than are wanted. If glass be made too soft it may fall so completely out of shape as to become unworkable except in very skilful hands. The following rules, therefore, should be strictly adhered to. Always employ in the first instance the smallest flame that is likely to do the work required. In operations involving blowing out viscous glass, attempt to blow the glass at low temperatures before higher ones are tried. ”

“ It is important that the point of hot glass used shall be very small, however. Even good glass will frequently give an irregular fracture if touched with a large mass of molten glass.
Finally, glass tube which is thin and of small diameter [15] should not crack when suddenly brought into a flame. But larger and thicker tubes will not often withstand this treatment. They should not crack, however, when they are brought into a flame gradually, after having been held in the warm air in front of it for a minute or so.
Good glass does not readily devitrify when held in the blow-pipe flame. ”

“ Another method of preventing one side of a tube from cooling down whilst the other is presented to the flame, is to place a brick at a short distance from the extremity of the flame. The brick checks the loss of heat considerably. A block of beech wood may be used for the same purpose, the wood ignites and thereby itself becomes a source of heat, and is even more effective than a brick.
Fuller details of the management of lead glass under various circumstances will be found in the subsequent descriptions of operations before the blow-pipe. ”

“ As it is frequently necessary to make additions, alterations, or repairs to purchased apparatus, it is best to provide supplies both of soft soda glass and lead glass, for though purchased glass apparatus is frequently made of lead glass, yet sometimes it is formed from the soda glass, and as it is a matter of some difficulty to effect a permanent union between soda glass and lead glass, it is desirable to be provided with tubes of both kinds. ”

“ Heat the open end of the closed tube, and either end of the other tube in a small flame until they are almost melted, taking care that only the ends of the tubes are heated, and not to let the glass be thickened; bring the two ends together with sufficient pressure to make them adhere, but not sufficient to compress the glass to a thickened ring. Before the joint has time to cool too much, adjust your blow-pipe for a pointed flame, if you are not already working with that kind of flame, and allow the point of the flame to play on any spot on the joint till it is heated to redness ”

“ This incrustation is very easily removed by re-heating the whitened surface, provided that the material has been kept scrupulously clean. If the silica has been brought into the flame when dusty, or even after much contact with the hands of the operator, its surface is very apt to be permanently injured. Too much attention cannot be given to cleanliness by the workman.
(3) When a heated tube or bulb of silica is to be expanded by blowing, it is best not to remove it from the flame, for if that is done it will lose its plasticity quickly unless it be large. ”

“ And though it is possible, with care, to employ the hot space immediately in front of the visible end of an ordinary brush flame, which is rich in air, yet, in practice, it will not be found convenient to heat large masses of lead glass nor tubes of large size, to a sufficiently high temperature to get the glass into good condition for blowing, by presenting them to the common brush flame. ”

“ If the stopper is to fit a tube contracted like B, it must be constructed from a piece of tube that will pass through the contraction at B. The tail GF will not do such good service as it does in the case of a tube which has been opened out to receive its stopper, but it will help to guide the stopper, and should be retained.
When the stopper has been ground into its place, melt off the tail at F. The flame must be applied very cautiously, as [54] glass which has been ground is particularly apt to crack on heating. ”

“ Management of Soda Glass.—In working with soda glass the following points must be constantly kept in mind. That as it is much more apt than lead glass to crack when suddenly heated, great caution must be exercised in bringing it into the flame; and that in making large joints or in making two joints near each other, all parts of the tube adjacent to that which, for the moment, is being heated, must be kept hot, as it is very apt to crack when adjacent parts are unequally heated. ”

“ My own Herapath blow-pipe only gives a satisfactory oxidising brush flame when the jet is removed altogether from the end of the air-tube. For producing pointed flames the finer jet of the air-tube must be used, but when a highly oxidising flame of large size is required it must be removed. The internal diameter of the central air-tube should be nearly half as great as that of the outer or gas-supply tube. Fletcher’s Automaton with the large air jet gives a very liberal supply of air, and produces an excellent oxidising brush flame. ”

“ To make a good U-tube of large size, and of uniform diameter from end to end, requires much practice, but to make a tolerably presentable piece of apparatus in which the two limbs are bent round till they are parallel, without any considerable constriction at the bend, can be accomplished without much difficulty. ”

“ In pulling apart the ends the scratch should be held upwards, and the pull should have a downward direction, which will tend to open out the scratch. In the case of a large tube, a scratch will not ensure its breaking clean across. The tube must be filed to some depth, half-way, or even all round it. A good [27] way of breaking a tube is to place the file in the table after scratching the glass, to hold the glass tube above its edge with one hand on each side of the scratch, and to strike the under side of the tube a sharp blow upon the edge of the file, directly beneath the scratch. ”

“ The beginner should work with a gauge and regulator on the bottle of oxygen, and should watch the consumption of oxygen closely. A large expenditure of oxygen does not by any means necessarily imply a corresponding output of silica, even by one who has mastered the initial difficulties. ”

“ When a very sharp bend is to be made, it is sometimes best to heat a narrow zone of the glass rather highly in the blow-pipe flame, and to blow the bend into shape at the moment of bending it, as previously described, one end having been closed for that purpose beforehand. ”

“ In the glass-works, where large quantities of ornamental and other glass goods are made of lead or flint glass, the pots in which the glass is melted are so constructed that the gases of the furnace do not come into contact with the glass ”

“ Hard glass is used for apparatus that is required to withstand great heat. It is difficult to soften, especially in large pieces. It should only be employed, therefore, when the low melting points of soda or lead glass would render them unsuitable for the purpose to which the finished apparatus is to be put. What is sold as Jena combustion tube should be preferred when this is the case. ”

“ As glass is much less expensive to work with than silica, the beginner will find it best to spend a few days working with the common gas blow-pipe and glass before he attempts to manipulate the new and more refractory material. ”

“ When a good joint has been made, the tube presents the appearance of A, Fig. 15, the union being at about bb. Next heat the whole tube between the dotted lines aa, and blow it into the shape of B in which the dotted line dd should correspond to the actual line of junction of the two tubes.
In making all joints it is important to leave no thick masses of glass about them. If the glass be fairly thin and uniformly distributed, it is less likely to break during or after annealing under any circumstances, and especially if it has to bear alternations of temperature. ”

“ A method much practised by the makers of sheet glass, and suitable for large objects, is to wrap a thread of hot glass round the tube, at once removing it, and touching any point of the glass which the thread covered with water or a cold iron, when a crack will be started and will pass round the glass where it was heated by the thread. ”

“ The ends to be joined, prepared as before, so that one slightly overlaps the other, must be held firmly in contact by clamps, and heated in successive portions by a blow-pipe held in the hand of the operator, each patch of glass being re-heated and gently blown, after a rough joint has been made. Finally, a larger flame may be used to heat up the whole joint for its final blowing. It is important to place the apparatus so that the operator has free access to it on all sides. A revolving table might be employed. An assistant [64] to work the bellows is necessary. ”

“ For use with lead glass the supply of air is rather too small, and does not enable one to get such good results. This can be easily amended, however. By slightly increasing the size of the air-tube of the smaller blow-pipe, and having increased the supply of air to the larger blow-pipe also, by reducing the external diameter of the end of the innermost tube, I now get medium-sized brush flames and pointed flames with this blow-pipe, that are equal to any I have used for heating lead glass. ”

“ The precise [4] heights that are desirable for the table and stool, and the exact position of the blow-pipe, will depend upon the height and length of arm of the individual workman, and it must therefore be left to each person to select that which suits him best. A moveable rest made of wood, for supporting the remote end of a long piece of glass tube a few inches above the table, whilst the other end is being heated in the flame, will be found convenient. ”

“ Large tubes may also be bent by rotating a sufficient length of the tube in a large flame till it softens, and bending in the same manner as in the case of smaller tubes, and after filling them with sand, closing one end completely, and the other so that the sand cannot escape, though heated air can do so. ”