TUBE, CANE, AND CHEMICAL GLASSWARE
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 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.
The iridescence and variety of colours yielded by the refraction of
light between the glass threads gives spun glass its peculiar effect,
very evident in the forms in which it is used in decorating small
ornaments such as forming the tails of glass birds.
Glass wool is made in a somewhat similar way, and is successfully used
as a non-conductive packing material for insulation from heat.
Glass frost or snow is made by blowing small gatherings of glass out to
a bursting point. These very thin shells are then crushed and the flakes
collected, and used for such purposes as surfacing sand paper or
decorating Christmas cards, being sieved to the requisite size and
affixed with a siccative to the paper.
Dolls’ eyes and artificial human eyes are made by well-trained operators
working before a blow-pipe flame and manipulating tube and cane of
delicately coloured tints to form the pupil and shell of the eye, the
veins being pencilled on with thin threads of red-coloured glass. A
considerable amount of skill and adaptation is necessary to do this
class of work, and much depends upon the matching of the coloured cane
glass used to give the natural effects. When properly made, so clever
and natural are these glass imitations of the human eye that it is with
difficulty that the ordinary observer can tell that they are not real. A
skilled worker will make the artificial eye to fit the muscles of the
socket and so move. In this way much ingenuity has been shown in fitting
the eye sockets damaged during the war.
Aventurine is a golden coloured glass containing minute yellowish
spangles or crystals reflecting upon each other and giving its peculiar
effect. This glass is obtained by the use of an excess of copper with
strong reducing agents in the glass, whereby the copper is partially
reduced within the glass, giving the pretty spangled effect. This glass
is often used in the form of jewel stones, being cut and polished and
fitted in ornaments. The process of making this glass was originated by
the Italians, and for some time it remained a secret with them, and even
now is styled “Italian aventurine.”
Chrome aventurine is another form, giving a green, spangled effect. This
is got by using an excess of chromium in the presence of reducing
agents.
The successful production of aventurine depends upon slowly cooling the
molten glass so as to assist crystallisation.
Mica schist, or flake mica, is used to give another curious effect in
glass. A gathering of some dark-coloured glass is rolled or marvered
upon a thin layer of flaked mica, and then a further gathering or
coating of clear crystal metal is made. The whole is then blown and
formed into some fancy ornament or vase. When finished, the glistening
mica flakes show through against the coloured background, giving a
curious silvery reflection.
------------------------------------------------------------------------