Extemporised Glass-Blowing Apparatus--The Use of Oil or
other Fuels--Making Small Rods and Tubes from Glass
Scrap--The Examination of Manufactured Apparatus with the
View to Discovering the Methods Used in Manufacture--Summary
of Conditions Necessary for Successful Glass-Blowing.
If, in the early stages of his study of glass-blowing, the student
should attempt to work with the very simplest appliances, it is probable
that his progress will be hindered; the use of the apparatus will
require an undue amount of care and his attention will be distracted
from the actual manipulation of the glass. The case is widely different
after he has acquired a certain facility in glass-blowing.
_A Simple Form of Blowpipe._--Although there are even more simple forms
than that described here, we are not concerned with them. The form
described is the simplest with which any considerable amount of
glass-blowing can be carried out with certainty.
This form consists of a tube through which air may be blown with the
mouth, a condensation chamber in which any moisture from the breath can
condense, a blowpipe jet, a supporting piece and a source of flame.
The tube, condensation chamber, and jet are combined in the ordinary
Black's blowpipe, such as is used for blowpipe tests in qualitative
analysis; it consists of a conical tin tube having a mouthpiece at the
small end and a side tube which carries a brass jet. A support for such
a blowpipe may be cut out of a piece of brass or tin-plate, and should
be fastened to a small, flat, wooden board. A source of flame may
consist of an ordinary brass elbow, such as is used on gas fittings, and
into which a piece of thin brass tube (the body of a fish-tail burner
from which the perforated non-metallic plug has been removed will serve
quite well) has been fitted. It is an advantage to flatten the brass
tube somewhat and to file the flattened end to a slope which corresponds
with the angle at which the blowpipe jet enters the burner. The whole
source of the flame should be mounted on a separate base, in order that
it may be moved while adjusting the apparatus to the best relative
positions of flame and blowpipe jet. The complete apparatus is shown by
_a_, Fig. 16.
[Illustration: Fig. 16]
In order to take full advantage of this blowpipe, it is desirable that
the student should learn to maintain a steady steam of air with his
mouth and, at the same time, be able to breathe. This requires a little
practice.
As a first exercise in breathing, before trying to breathe while using
the mouth blowpipe, the student should close his mouth and inflate his
cheeks with air; now, still keeping his cheeks tightly inflated, he
should attempt to breathe through the nose. At first, this may be found
rather difficult, but it becomes remarkably easy after a little
practice. When he has mastered this, the student may practise the same
operation, but with the blowpipe. It is important to bear in mind that
the cheeks, not the lungs, form the reservoir for air used in
maintaining the blowpipe flame. After a while, the student will find
that he can maintain a steady air pressure and yet breathe with complete
comfort.
In adjusting the flame, care should be taken not to blow so hard as to
produce a ragged and noisy cone of fire. A small jet, such as that
commonly used on a mouth blowpipe, will with care give a pointed and
quiet flame, having an appearance similar to that shown in the
illustration.
With a blowpipe like this, it is quite easy to seal glass tubes up to an
inch in diameter, to join tubes up to half an inch in diameter, to bend
tubes, to blow small bulbs, and to make the simpler forms of internal
seal; but the provision for condensation of moisture is not ideal, and
prolonged use of such a blowpipe also tends to produce undue fatigue.
_A Mouth Blowpipe With an Expanding Reservoir._--This form of blowpipe
can be made to give most excellent results; it is highly portable, and
does not produce nearly so much fatigue when used continuously as the
blowpipe described in the last section. Various slight modifications
have been made in its construction during the last eighty years, but
that described below will be found quite satisfactory.
The apparatus consists of a tube through which air is blown from the
mouth, a valve through which the air passes into an expanding reservoir,
and a blowpipe jet in communication with the reservoir.
In making the valve, several essentials have to be remembered; it must
allow a free passage of air into the reservoir, it must open easily, and
must close quickly. A satisfactory form of valve is that shown by _b_,
Fig. 16. The moving part consists of a light glass bulb of about
three-eights of an inch diameter and having a glass stem of rather under
one-eighth diameter and about an inch and a half long. This stem rests
in a guide at the end of a brass tube, the bulb contacting against the
other end which is approximately shaped. The bulb and its seating are
ground air-tight. A very light spring holds the bulb in position.
This valve is fitted into a metal or glass T piece, one limb of which
leads to the air reservoir and the other limb leads to the blowpipe jet;
the limb containing the valve leads to the tube through which the air is
blown in.
A convenient reservoir may be made from a fairly large football bladder.
A network of string should be fitted over the outside of the bladder and
the strings should terminate in a hook on which a weight can be hung, in
order to provide a means of adjusting the pressure at which the air is
delivered to the jet. This bladder should be washed out and allowed to
drain after use.
The air tube which passes from the valve to the mouth may conveniently
be made of brass, but, in order to avoid the continued contact of metal
with the lips of the operator, it should be fitted with a non-metallic
mouthpiece. It is an advantage from the point of view of portability to
have the air tube easily detachable from the T piece containing the
valve.
The blowpipe jets, of which there may be several with advantage, may be
made of glass tubing, bent to the most convenient angle and having an
enlargement or bulb at some point in the tube. This bulb serves as a
final condensing place for any traces of moisture that may escape from
the larger reservoir.
The whole device, blowing tube, reservoir, and T piece may be fastened
to a clamp, so that it can be secured on the edge of any table where
blowpipe work is to be carried out. If the blowpipe is to be used with
gas, the form of burner described under. "A Simple Form of Blowpipe"
will be found quite satisfactory.
_The Use of Oil, or Other Non-Gaseous Fuels._--Although gas, when
available, is usually preferred on account of its convenience, there are
several other fuels which give a hotter flame. They have, also, the
additional advantage of not requiring any connecting pipes; but each has
its own disadvantage.
One liquid fuel deserves special mention as being rather less desirable
than the others; this is alcohol. Although very convenient in use, it
has the disadvantage of being rather too highly inflammable and capable
of burning without a wick, thus involving a certain fire risk; the flame
is scarcely visible in a bright light, and the heat given by either the
ordinary flame or the blowpipe flame produced from alcohol is
considerably less than that from a similar flame in which coal gas is
used. For small work, however, the facility with which a spirit lamp may
be lighted may more than counterbalance these disadvantages at times.
_Paraffin Wax._--Where there is no coal gas available and the blowpipe
is only required at intervals, and especially where high portability is
required, there are few fuels so convenient as paraffin wax. This may be
obtained in pieces of a satisfactory size by cutting paraffin candles,
from which the wick has been withdrawn, into lengths of about half an
inch. These cut pieces have the advantage over any oily fuel, such as
colza oil, that they can be wrapped in paper or carried in a cardboard
box; further they will keep indefinitely, even in the presence of air,
without undergoing any perceptible change.
_Forms of Lamp for Paraffin Wax._--Probably, the best form is that
devised by Thomas Bolas, and described by him in the _Journal of the
Society of Arts_, December 2nd, 1898. This lamp consists of a small open
tray of iron, through which pass three or more flat tubes, and between
these tubes are placed small flat pieces of wick, the fit being such
that the pieces of wick may be adjusted easily by means of a pair of
pointed tweezers.
The flame thus obtained, instead of having one large hollow, is broken
or divided so that the combustion is concentrated into a smaller area,
and the air blast, which is directed across the flame, carries the flame
with it in a more complete manner than is the case with the ordinary
flame; a more thorough combustion being realised by this arrangement.
Another advantage is the ease with which the wick may be changed and a
larger or smaller wick inserted to suit the flame to any size of air
jet.
This form of lamp may be used for oily fuel, although it is specially
suitable for paraffin wax.
Two small pieces of bent tin-plate may be used as side covers, and these
serve to adjust the flame within certain limits. A tin-plate cover which
fits easily over the whole lamp serves as an extinguisher. The complete
lamp is shown by _d_, Fig. 16, and this figure shows also a quick-change
air-jet device, the whole arrangement forming a blowpipe for use where a
non-gaseous fuel is to be employed.
Although the lamp just described is desirable when complete control over
the size of the flame is necessary, and if the ideal conditions and
maximum heat are to be obtained, yet a simpler form of lamp will be
found to give very good results. Such a lamp may consist of a flat tin
tray, having a diameter of about three and a half inches and a depth of
about one inch. In this tray is a tin support for the wick, and the wick
itself may consist of a bundle of soft cotton, for example, a loosely
rolled piece of cotton cloth, but in either case the top of the wick
should be cut to approximately the same angle as that at which the
blowpipe jet meets the flame.
In using paraffin wax as a fuel, it is necessary to see that sufficient
wax reaches the wick to prevent charring during the first few minutes
before the bulk of the wax is melted.
_Animal and Vegetable Oils._--Almost any oil may be used as a fuel, but
many tend to become hard and gummy if allowed to stand in the air for
any considerable time. When this happens, the wick becomes clogged and
it is impossible to obtain a good flame. A number of the oils tend,
also, to produce rather strongly smelling smoke.
_A Flame-Guard for Use With Non-Gaseous Fuels._--In order to avoid the
eye-strain produced by the luminous base of the flame from a wick
burning paraffin wax or oil, it is often advantageous to make a small
tunnel of tin-plate, which can be rested on the sides of the lamp and
rises over the top of the wick. Such a flame guard is shown by _e_, Fig.
16.
_Small Rods and Tubes from Glass Scrap_:--It is scarcely practicable to
make small quantities of good glass with the blowpipe flame as the only
source of heat, but it is less difficult to make small rods or tubes
from glass scrap, and the ability to do this is sometimes of
considerable value when a small tube has to be joined on to some special
piece of apparatus made of glass of unknown composition. It may be
possible to obtain some fragments of similar glass, either from a broken
part of the apparatus or from a similar piece, and from these fragments
small tubes or rods can be made.
The fragments of glass may be melted together on the end of a clay
pipe-stem, care being taken to avoid trapping air bubbles as fresh
fragments are added to the molten mass. When a sufficient quantity of
glass has been accumulated, the viscous mass may be drawn out into a rod
by bringing another pipe-stem into contact with the hot mass, rotating
both pipe-stems steadily, and separating them until a rod of the desired
size has been obtained.
If, on the other hand, it is desired to produce a tube from the mass of
heated glass, the mass should be blown hollow before the pipe-stems
supporting it are separated.
_Methods of Manufacture._--When the student has familiarised himself
with the more common operations and processes used in glass-blowing, he
will be in a position to increase his skill and knowledge of special
methods by a critical examination of various examples of commercial
work. There are few exercises more valuable than such an examination,
combined with an attempt to reconstruct the stages and the methods by
which the article chosen for examination was made.
Obviously, it is impossible to give full details of all constructions in
a small text-book; but it is easy to give an example of the
constructional methods employed in the making of almost any piece of
light blown-glass apparatus, and these methods should prove of special
value when apparatus of a new pattern has to be evolved for the purposes
of research. That is to say, one designs the apparatus required, applies
known methods of construction as far as possible, and, by the
examination of commercial apparatus having similar features, evolves the
new methods required. For an exercise in such a process of
reconstruction we may well take an ordinary commercial vacuum tube, such
as that shown by _a_, Fig. 17.
[Illustration: Fig. 17]
In the tube from which this drawing was made, it was found that the
spiral in the middle bulb was of a slightly yellowish colour and gave a
green fluorescence when the electric discharge was passed through the
tube; that is to say, the spiral is made of uranium-glass, which is
usually a soda-glass containing trace of uranium, and hence differing
slightly in composition from the ordinary glasses. The two enclosed
tubes which are bent into a series of S bends gave a pink fluorescence,
which indicates lead-glass; and the remainder of the tube fluoresced
with an apple-green colour; this suggests ordinary soda-glass. We have,
therefore, a piece of apparatus in which three dissimilar glasses are
joined, while, at the same time, that apparatus contains a number of
internal seals, and it is not probable that the dissimilar glasses will
have their coefficients of expansion so nearly alike as to permit of a
stable internal seal being made if one part of the seal consists of a
glass differing from that of the other part.
These considerations lead us to a closer examination of the joins where
the dissimilar glasses are introduced, and we find that in no case is
the internal seal made between dissimilar glasses, but that a soda-glass
extension is joined on to both the uranium-glass tube and the lead-glass
tubes at a point about half an inch before the internal seal commences.
Careful examination of these joins shows that the change from one glass
to another is not abrupt but gradual. Such a transitional joint may be
made by taking a length of soda-glass tubing, sealing the end and fusing
a minute bead of the other glass on to the sealed end, the end is then
expanded and another bead of the other glass added, this bead is
expanded and the operation is repeated, thus building up a tube, and,
finally, the tube of the other glass is joined on to the end of this.
We are now concerned with the question of the insertion of the
uranium-glass spiral into the bulb (see p. 38). Obviously the spiral is
too large to pass through the necks of the bulb, and it is difficult to
imagine that the spiral was obtained by the insertion of a length of
straight tubing which was bent after entering the bulb; therefore, the
only remaining method is that the spiral was made first and the
soda-glass extensions fastened on, and that the bulb was blown, cut in
halves and the spiral inserted, and the two halves were then rejoined.
That this was actually the case is confirmed by traces of a join which
are just visible round the middle of the bulb. The insertion of the
spiral and the making of the first internal seal are shown by _b_, and
_c_.
There is one detail in making the second join of the spiral to the bulb
which calls for attention, and the small branch, similar to an
exhaustion branch, at the side of the bulb provides a clue to this. If
an attempt were made to complete the second internal seal through a
closed bulb it would be impossible to obtain a good result, as the
air-pressure in the bulb would not be under control when once union was
effected, and further heating of the air in the bulb would cause
expansion and perforate the wall near the second internal seal; we
therefore make a small branch which can be left open and through which
such air-pressure as may be found necessary can be maintained.
The third join, by which the lead-glass tube is joined to the soda-glass
is made in stages similar to those in which the soda-glass and
uranium-glass were joined; but the internal seal is most conveniently
made by sliding a length of tubing over the lead-glass and fusing this
tubing to the large diameter soda-glass tube to which the lead-glass is
already joined. The first stage of this operation is illustrated by _d_.
When this seal is completed, the end of the soda-glass tube is drawn off
and sealed as shown in _e_, and at this stage a side tube or branch is
joined on. The sealed end of the outer and large diameter soda-glass
tube is heated until it contracts and fuses to the enlargement that has
previously been joined to the lead-glass tube, and the end is burst out
as shown in _f_. Another length of soda-glass is then joined on to the
burst-out end, and this length of soda-glass tubing is drawn out to a
thin-walled contraction; the non-contracted part is expanded to form the
bulb, and a small exhaustion branch made on the side, the drawn-out
portion being cut off, and an electrode, previously prepared by coating
a part of its length with a suitable enamel, is introduced. The tube is
tilted to keep the electrode away from the drawn-out end, which is
melted off and sealed. A small perforation is made with a hot platinum
or iron wire in the sealed end, the electrode is shaken into position,
and the sealing is completed as explained on page 42.
The remainder of the tube, that is to say the lead-glass tube and the
bulb on the other side of the middle bulb, is completed in a similar
manner.
SUMMARY OF CONDITIONS NECESSARY FOR SUCCESS IN GLASS-BLOWING.
For the convenience of the student, it may be well to summarise the
chief essentials for success in glass-blowing, and at the same time to
add such brief notes on the various methods as may seem desirable.
_Adjustment of Blowpipe._--The air jet should be clean internally, and
so centered as to give a flame having a well-defined blue portion, the
tip of the flame should not be only slightly luminous but purple in
colour. In the case of a blowpipe burning oil or wax fuel the flame may
be a trifle more ragged without disadvantage.
_Bellows and Blowing._--The bellows should be adjusted to deliver air at
constant pressure, either by insertion of a tap or, better, by attention
to the wind reservoir if necessary. The movement of the foot in blowing
should be steady, not jerky.
_Heating Glass._--The tube or rod should be heated cautiously until it
has reached its softening point in its thickest part. Steady rotation of
the glass during the heating is almost essential.
_Blowing a Bulb or Expanding a Join._--Prolonged heating is necessary in
order that the thick parts may be heated completely through. Blowing
should take place by stages, in order that the thin parts, which tend
to expand first, have time to cool. The thick parts can then be expanded
by further blowing and thus a bulb or expansion of even thickness can be
obtained.
_Cutting Glass._--The most useful method for general use is by means of
the file or glass-blowers' knife. Either file or knife must be kept
sharp by grinding. Neither file nor knife should be used on hot glass.
The diamond and wheel cutter are useful for cutting sheet-glass, and
when the diamond is employed a singing noise is an indication of a
satisfactory cut.
_Leading a Crack._--A crack may be led in any desired direction by means
of a bead of hot glass or a small gas flame. The glass which it is
desired to crack should be heated at a point slightly in advance of the
crack, which will extend in the direction of the source of the heat.
_Turning Out the End of a Tube._--This is done by heating the end of the
tube and rotating it against an iron rod. The rod must be kept polished
and free from rust, and it must not be allowed to become too hot while
in use, otherwise the glass will stick to it.
_Joining Unlike Glasses._--Joints between unlike glasses are often
unstable. When such joints are made it is desirable to blow them as thin
as possible, and to avoid the junction of unlike glasses in any complex
joint, such as an internal seal. A transitional portion of tubing may be
built up by the successive addition and interfusion of beads of one of
the glasses to the end of a sealed tube consisting of the other glass.
_Joining a Tube to a Very Thin Bulb._--The bulb may be thickened at the
point of union by fusing on a bead of glass and expanding this slightly.
A small central portion of the expanded part may then be perforated by
bursting and the tube joined on.
_Insertion of One Bulb Within Another._--A bulb may be divided into two
halves by leading a crack round it and the inner bulb is then
introduced. The two halves of the outer bulb may be fitted together
(care being taken to avoid any damage to the edges), and the bulb may be
completed by rotating the contacting edges before the blowpipe until
they are soft, and then expanding slightly by means of air-pressure.
_Annealing._--For most purposes, in the case of thin, blowpipe-made or
lamp-blown glass apparatus, it is sufficient to cool slowly by rotating
the finished article over a smoky flame and setting it aside in a place
free from draughts, and where the hot glass will not come in contact
with anything.
Simple bulbs and joints do not even need this smoking; but thick
articles, and especially those that are to be subjected to the stress of
grinding, need more prolonged annealing in a special oven.
_Use of Lead-Glass._--When lead-glass is to be used, the blowpipe flame
should be in good adjustment and the glass should not be allowed to
approach so near to the blue cone as to be blackened. Slight blackening
may often be removed by heating the glass in the extreme end of the
flame.
Lead-glass articles tend to be rather more stable than similar articles
of soda-glass.
_Combustion-Glass._--This may be worked more easily if a small
percentage of oxygen is introduced into the air with which the blowpipe
flame is produced. If the air is replaced entirely by oxygen there is a
risk of damaging the blowpipe jet, unless a special blowpipe is
employed.
_Internal Seal._--There are two ways of making these, one, in which the
inner portion of the tube is fused on to the inside of the bulb or tube
through which it is to pass, an opening is made by bursting and the
outer tube is joined on. This is a quick and in some ways more
satisfactory method than the other, in which there is no separate inner
piece.
_Rubber Blowing Tube._--In complicated work it is often convenient to
use a thin rubber blowing-tube which is connected with the work either
by a cork and piece of glass tubing or by fitting over a drawn-out end.
The use of such a blowing-tube avoids the inconvenience of raising the
work to the mouth when internal air-pressure is required. One end of the
rubber tube is retained in the mouth during work.
_General Notes._--A large amount of glass-blowing is spoiled through
carelessness in arranging the work beforehand. The student should have
every detail of his manipulation clearly in mind before he commences the
work; he should not trust to evolving the method during the actual
manipulation.
Undue haste is another fruitful source of failure. Practically every
operation in glass-blowing can be carried out in a perfectly leisurely
manner, and it is better to err rather on the side of deliberation than
on the side of haste.
If, as will doubtless happen at times, a piece of work gives trouble and
it is necessary to pause and consider the whole question, or if for any
other reason it is necessary to stop during the construction of a
partially finished join or other operation, great care should be taken
not to allow the work to cool. A large, brush-like flame may be produced
by increasing the amount of gas admitted to the blowpipe, and the work
should be held just in front of the current of hot air produced by such
a flame.
It will then be possible to continue work on this without causing it to
crack when further heat is applied.
As time goes on, the student will find an increasing confidence in his
ability to manipulate the soft glass, and with increasing confidence
will come rapidly increasing power of manipulation. Perhaps the greatest
obstacle to success in glass-blowing is undue haste in manipulation.
INDEX
Absorption bulbs, 21, 23.
Airtube, flexible, 8, 102.
Alarm thermometer, 45.
Annealing, 7, 60.
Bellows, adjusting pressure of, 5, 6.
Bellows, foot, 5, 6.
Bending tubes, 23.
Blackening, 58, 101.
Branching, 18, 19.
Brushes of spun glass, 53.
Blowpipe flame, quality of, 3.
Blowpipe for mouth blast, 80, 82, 84.
Blowpipe, for paraffin wax, 82, 88.
Blowpipe, Herepath's, 2.
Blowpipe jet, centring, 3, 98.
Blowpipe jet, dirt in, 3.
Blowpipe jet, multiple, 4, 40.
Blowpipe, Letcher's, change, 4.
Blowpipe, simple form of, 80.
Bulb, medially on tube, 22.
Bulbs, 19, 20, 22, 38, 98.
Bulbs, absorption, (Liebig's), 21, 23.
Bulbs, dividing, 39, 95.
Bulbs from rod, 25.
Bulbs, internal, 38.
Bulbs, thick, 21.
Cages, from glass rod, 24, 25, 27.
Calibration, 72.
Carius tubes, 16.
Condenser, Liebig's, 37.
Condensers, various, 37, 38.
Cone, carbon, 8.
Crack, leading, 30, 99.
Cracking, subversive, 103.
Cutting glass with diamond, 30.
Cutting tubes, 11, 99.
Diamond (glazier's), use of, 30.
Dissimilar glass, joining of, 22, 94.
Drilling, 61.
Electrodes, sealing in, 42, 97.
Etching glass, 70.
Extemporised appliances, 80.
Examination of apparatus, 93.
Failure, Haste chief Source of, 103.
Failures, Notes as to, 97.
File, with oblique ground edge, 7.
Filing glass, 63.
Filter pumps, 35
Foot, 25
Fuels various, 82, 86, 87, 89.
Funnel, thistle, 23.
General principles and precautions, 1, 97
Glass, varieties of, 9, 55, 91-97.
Graduation, 72-76
Haste, Source of Failure, 103
Heat reflector, asbestos, 7.
Heating, intensive, 7, 57.
Heating precautions, 12, 98
Joining dissimilar glass, 22.
Joining glass to metal, 76.
Joining tubes, 16, 94, 100.
Knife, Glass blower's, 7, 99.
Lenses, grinding, 63.
Marking glass, 69.
Methods, analytic study of, 91, 93.
Oxygen for intensive heating, 57, 101.
Precautions and General Principles, 1, 97.
Pumps, Filter, 35.
Pumps, Sprengel, 49, 50.
Re-entering branch, 40.
Reflector of heat, asbestos, 7.
Rod, uses and articles from, 17, 25, 27, 28.
Rod, blowing to hollow, 17, 25, 26, 91.
Scrap glass, working, 90.
Sealing tubes, 12, 13, 14.
Sealed tubes for pressure, 15, 16.
Sealing in of Electrodes, 42, 97.
Seals, internal (airtraps), 32, 102.
Silvering glass, 77.
Soldering glass, 76.
Soxhlet-tube, 40.
Spirals, 23, 95.
Spray arrester, 34.
Spray producers, 36.
Sprengel pumps, 49, 50.
Spinning glass, 51.
Stopcocks, 60, 66.
Stoppering, 63.
Stirrers, 28, 29.
Summary as to precautions and failures, 97.
Taps, 60, 66.
Thermometers, Various, 44-49.
Thermo-regulator, 24.
Thistle Funnel, 23.
Tools, Various small, 7.
Turn-pins, 7, 8, 99.
Turning out open ends, 14, 99.
PRINTED IN GREAT BRITAIN BY
W. JOLLY & SONS, LTD., PRINTERS, ABERDEEN.