Laboratory and chemical glassware consists of thin blown ware in the form of flasks, beakers, test tubes, etc., used in chemical operations. Most of these goods are blown in hinged moulds mechanically or automatically operated by the worker. The lips and flanges of the necks are neatly formed afterwards by re-heating and working the edge to a form allowing them to pour cleanly, and prevent any fluid contained therein from running down the sides of the flask or beaker whilst in use. The heavier glassware, in the form of desiccators, measuring cylinders, specimen jars, and three-necked bottles, are made by handwork. Chemical apparatus has necessarily to be made from a permanent stable highly refractory glass, so as to resist the solvent actions of mineral acids, alkaline solutions, and boiling water, as well as sudden changes in temperature.
The manufacture of tube and cane glass for various purposes forms a large and extensive portion of the glass trade. Considerable quantities of tube and cane glass in various sizes are used by lamp workers in the manufacture of certain forms of chemical apparatus and filling electric light bulbs. By re-heating glass tube and working before a blow-pipe flame, the various forms of test tubes, pipettes, burettes, soda-lime U-tubes, and condensers are made. Generally, for chemical apparatus two classes of tube are made, one a soft soda tube, and the other hard combustion tubing. Particular care has to be devoted to the grading and sorting of the various sizes. The bore of the tube, the thickness of the walls, and the outside width have all to be checked and the lengths classed accordingly.
In the manufacture of tubing, unless the glass is of large size or great thickness, it is not annealed, and shows a case-hardened condition which materially increases the strength of the tube to resist internal pressure, as is the case with boiler gauge tubing. In the manufacture of apparatus from tube and cane, care must be taken that the various pieces used in welding together the different portions of the apparatus should be of the same temper and composition, and supplied from one source, so that they may join and work perfectly together.
The lamp worker or glass blower should take care to get his supplies from a reliable source, so that the glass pieces will be adapted to work together. Trouble occurs when odd tubings from various makers are worked together. The same applies to fancy glass working, where various coloured canes are worked into ornaments. Reputable firms can always supply from stock such colours and tubing properly adapted for their specific purposes, and they take every precaution to see that the various colours join and work together. Supplies of glass rod can be had that will join on to platinum, nickel, iron, or copper wire with sound joints.
In making cane glass, the workman gathers sufficient metal upon a pontil: for thin cane he would gather less than for heavy thick cane. After gathering, he marvers the metal into the form of a solid cylinder. Meanwhile, an assistant gathers a little metal on a post or pontil with a flattened end. The metal he has gathered has covered the flat end of the post, and he holds this in readiness for the workman, who is now re-heating the cylinder of glass at the pot mouth. As the cylinder of glass becomes soft, he withdraws it and allows the end of the cylindrical shaped mass of glass to fall gently upon the flat end of the post, to which it adheres. They then carry the glass between them to a wooden track or run-way, along which they walk at a smart pace in opposite directions; stretching out the hot glass between them, it gradually thins out and rests on the floor. The pace the men separate apart from each other is regulated according to the thickness of the cane desired: for very thin cane a smart trot is necessary, but for a thick cane a slow walk is sufficient. As the glass is drawn out it is allowed to rest on wooden supports, and when cool is cut up into convenient lengths by scratching the glass with a steel file. These lengths are collected and bundled up for sorting and classification. All portions distorted or over-size are returned as cullet for re-melting and re-use.
In tube making, instead of a solid cylinder as in cane making, the workman, by gathering the glass on a blow-iron and blowing and marvering it, obtains a thick-walled, hollow, cylindrical form. This is re-heated and the end stuck to a post and drawn apart as before described in cane making, forming a tube of a width proportional to the rate the two have travelled apart in drawing it out, and to the quantity of metal gathered. In this way the respective sizes and thicknesses are regulated. A narrow cane or tube may be drawn out for 300 ft., but for a thick or wide one probably only 30 ft. may be drawn. In making the larger widths, some method, of cooling, or fanning, is adopted, to ensure uniform size by cooling the hot glass quickly as it is drawn out. It is evident that, whatever shape is given to the original mass of glass whilst being mar-vered, the tube will bear a similar shape in proportion, either within or outside the glass. In this way, square, triangular, or oval sections can be produced in both tube and cane.
The manufacture of white opal, coloured cane, and tube is carried out on like methods to those used in ordinary cane and tube making.
We will now describe the manufacture of Filigree. This is rod or tube containing opal or coloured threads, either straight, spiral, or interlaced within a transparent glass; these threads follow the whole length of the cane or tube.
This curious form of glasswork was originated by the Venetians,' who are exceptionally skilled in producing some elegant and ornamental filigree decorated glassware.
The method of producing filigree cane consists of first taking a number of short lengths of opal or coloured cane previously drawn and cut to about 6 in. lengths. These are then placed in vertical positions around the inner circumference of an iron cup mould, which may be about 5 in. in diameter. The opal strips of cane are supported vertically in small recesses provided in the rim of the mould at equidistant intervals. A ball of hot crystal glass is gathered on a pontil and is lowered into the inside of the mould, the hot metal coming in contact with the opal strips of glass adheres to them, and upon withdrawing the glass it brings the opal strips away with it arranged in sections round the circumference of the ball of glass. This is now re-heated and marvered until the canes or strips of opal are well embedded in the hot glass. Then the workman gathers another coating of hot glass over the whole, marvers it again into a cylindrical form, and then proceeds to draw it out as described in cane making.