Glass and Glass Manufacture

by Percival Marson

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 marvered, 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.

If a spiral form of lines is desired, the workmen, whilst drawing out the cane, turn or twist the pontil and post in contrary directions. These rotations cause the opal veins or threads to assume a spiral or twisted form within the glass. Various coloured cane may be used in the above process, and by placing them in alternate positions to the opal strips within the cup mould some very pretty and curious filigree work is obtained. These twisted filigree canes are used and manipulated over again in the process of making the various Venetian goblets and wine stems. Some fine effects in the application of filigree decoration can be seen in the specimens of Venetian glassware exhibited in the British Museum.

Millefiore work is produced by the workman, first spreading a layer of an assortment of small coloured glass chips of varying sizes (between 1/8 and 1/4 in. cube) over the face of the marver, and then taking a gathering of crystal metal on his blow-iron and rolling the ball of hot glass into the coloured mixture on the marver. The hot glass collects up a coating of the coloured chippings, and is then re-heated and again marvered, another gathering of crystal metal is made, which incases the whole. This is then blown out and worked into some form of ornament, such as a paper weight, inkpot, or bowl, producing a curious result that shows blotches of colours embedded within the glass, the effect of which is increased if a backing of opal glass has been used in the first gathering: this shows the coloured effect against a white background.

Spun Glass. Another curious form of glass is the spun glass which is much employed in making fancy ornaments. Glass can be spun into a thread so fine and flexible that it can be worked into a fabric like any textile material. In this way, glass ties can be made by plaiting the spun glass threads into the required form. Spun glass fibre is used in making the brushes used for cleaning metals with acids. On account of its greater resistance to acids than is shown by ordinary cloth, an endeavour is being made to use spun glass cloth in certain industries as a commercial application. Spun glass is used for making a form of filter cloth which is being used successfully in filtering acid residues in certain chemical processes, and, no doubt, when the elasticity and strength of the glass threads can be more developed, the scope for its use in other industrial processes will be increased.

The method of making spun glass thread consists in melting the end of a plain or coloured glass rod (which may be square, round, or triangular in section) in a blow-pipe flame and grasping the end which is melting with a pair of pincers, drawing it out and affixing it to a wooden drum, which is turned rapidly away from the glass being heated. The drum may be 2 or 3 ft. in diameter, and as the glass is continually fed into the heat it is drawn out into a very thin thread by the rapidly revolving drum, and coiled up until a sufficient quantity has been obtained. The thread is then cut across the drum, collected, and used for plaiting or braiding into the fabric or cloth.