When the glass is softened, you draw out the

tube, or push it together, according as

you

desire to produce a hollow in the surface of the tube, or to have the surface even, or to causea ridge to riseabove it.

A

cherry red heat isthe proper temperaturetoemploy.

6. SEALING.

If thesidesofthe tubeto be sealed arethin,

and

itsdiameter ^is small, it is sufficientto ex-pose the end that

you

wish to close to the flame ofthelamp.

When

^theglassissoftened

itsinks ofitself,inconsequence of the rotatory motion given to it, towards the axis of the tube,

and becomes

rounded.

The

application of

no

instrumentis necessary.

If thetube is of considerable diameter, or ifthe sides are thick,

you must

soften the end,

and

then, with ametallic rod oraflat pairof pliers,

mould

the sides to a hemisphere,

by

bringing the circumferencetowardsthe centre,

and

continuing to turn the tubeinthe flame, untilthe extremityis wellsealed,

and

perfectly round.

Examples

of the figure are tobeseen inpi.2,^fig. 3

and

5. Instead ofthis method,

itisgood,

when

the extremity is sufficiently softened, to

employ

an auxiliary tube, with the help of

which you

can abruptly

draw

out the point of the original tube,

which

be-comes by

that

means

cut

and

closed

by

the flame. In order that this part

may

be well

THE ART

rounded,

you may,

assoonasthetubeissealed, close theother extremity with^a ^littlewax,

and

continue to expose the sealed parttothe flame, untilithas

assumed

theformof adrop of^tallow.

Seepi. 2,fig. 15.

You

can also seal in this fashion,

^y

^blowing, ^with precaution, in the open

end^f

the tube, while the sealed end is in a softenedstate.

you

desire the sealed partto beflat, like pi. 3, ^fig. 30,

you must

press it, whileitis soft, againstaflatsubstance. If

you

wishitto beconcave,like thebottomof abottle,orpi. 3, fig. 2,

you must

suckairfromthe tubewith the

mouth

_; or,instead ofthat, force the softened end inwards with a metallic rod.

You may

also draw out the

end

^till ^it be conical, as pi. 2,^fig.4, orterminate itwith a^little button, as pi. 2, fig.6. In

some

cases the sealed

end

isbentlaterally_; inothers it is twirledinto a ring, having previously been

drawn

out

and

stoppedinthe bore. In short, the form given to the sealed

end

of a tube can

be

modifiedin aninfinityof ways, accordingto the objectfor whichthetube

may

bedestined.

You

should take care nottoaccumulatetoo

much

glass at the place of sealing. If

you

allowittobe too thickthere,

you

run therisk of seeingitcrack during the cooling.

Some

farther observationson sealingwillbe found at the article

Water Hammer,

in a subsequent section.

The

^operation of sealing succeeds bestatacherry-red heat.

BLOWING.

The

construction of a great

number

philo-40 THE ART

OF GLASS-BLOWING.

sophical instruments requiresthathe

who would make

themshould exercise himself in the art of blowing bulbs possessing a figure exactly spherical. This is one of the most difficult operations.

To blow

abulb at theextremity of a tube,

you commence

by sealing it

; after which,

you

collect at thesealedextremity

orless glass, accordingto the size

and

the solidity which

you

desire to giveto the bulb.

When

the endof the tube is

made

thick,completely sealed, andwell rounded,

you

elevate the tem-peratureto a reddish vjJiite heat, taking care toturnthetube continually

and

rapidlybetween yourfingers.

When

the end is perfectly soft

you

removeitfrom theflame, and, holding the tube horizontally,

you

blow quickly with the

mouth

into the openend, withoutdiscontinuing fora single

moment

the

movement

of rotation.

If the bulb does not

by

this operation acquire the necessarysize,

you

soften it again in the flame,while undertheaction ofwhich

you

turn

it veryrapidly, lest it should sink togetherat the sides, and

become

deformed.

When

itis sufficientlysoftened

you

introduce,in the

same manner

asbefore, afreshquantity ofair. Itis of importancetoobservethat,ifthetubebe of alargediameter, itisnecessaryto contract the

end

by which you are to blow, in order that it

may

beturnedround withfacilitywhileinthe mouth.

When

thebulb which

you

desire to

make

is to be

somewhat

large, it is necessary, after havingsealedthe tube,to softenitforthe space of about half aninchfrom its extremity, and

then, withthe aid of a flatpiece of metal,to pressmoderately

and

repeatedlyonthesoftened portion, until the sides of the tube which are thus pressedupon,sink together, andacquire a certain degreeof thickness.

During

this ope-ration, however,

you must

take care to blow,

now and

^then,^{into the} ^tube,ⁱⁿ^order ^to ^retain ahollow spacein the midst of the little

mass

ofglass,

and

tohindertheboreofthetubefrom beingclosed up.

When you

have thus,atthe expenseofthe length ofthe tube,accumulated at its extremity a quantity ofglass sufficient toproducea bulb,

you

have nothing

to do than toheat the mattertill it israisedtoa temperature

marked by

are.ddish-white colour, and thento

expand

by

blowing.

Instead ofaccumulatingtheglass thus, it is

expedientto

blow

onthe tube a series of

littlebulbsclose tooneanother(seepi. 1,^fig.8),

and

then,

by

heating theintervals,and blowing, tounite these little bulbs into a large one of convenient dimensions.

We

^have already observed, and

we

repeat here, that it isindispensably necessarytohold the glass out of the flame during the act of blowing. This is the only

means

of maintain-ing uniformity of temperature in the whole softened parts of thetube, withoutwhichit is

impossibleto producebulbs withsidesof equal thicknessin alltheirextent.

When

you desire toform abulb at the ex-tremity ofa capillarytube, thatisto say, of a tube

which

has abore of very small diameter, suchas thetubeswhichare

commonly employed

2 42 THE ART

OF GLASS-BLOWING.

to form thermometers, it

would

beimproperto

blow

itwith the

mouth

_; were

you

todoso, the vapour which

would

be introduced, having a greataffinity forthe glass,

would

soonobstruct thelittle canal, and presentto the passage of the aira resistance, which, with the tubes of smallestinteriordiameter,

would

often be in-surmountable. But, even

when

thetubes

you employ

have not so very small an internal diameter,

you

should still take care to avoid blowing withthe

mouth

_; becausethe introduc-tionofmoisturealwaysinjuresfineinstruments,

and

it is impossible to dry the interior of a capillarytube

when

once it has

become

wet.

Itisbetter to

make

use of a bottle of Indian rubber,which can be fixed on the open

end

ofthetube

by means

of a cork with a hole bored throughit.

You

pressthe bottle in the hand,taking careto hold the tube vertically, withthe hot part

upwards

_; if

you

werenotto take this precaution, the bulb

would

be turned on one side, or

would

exhibit the form of a pear, becauseit isimpossible, in this case, to giveto the massin fusion that rotatory motion whichis necessary,

when

the tubeis held hori-zontally, to the production of a globe perfectly spherical in its form,

and

withsidesof equal thickness.

Whenever

you

blow

into a tube

you

should keep the eye fixed on the dilating bulb, in order to be able to arrest the passage of air at the proper

moment.

you were

not to attend tothis, you

would

run the riskof giving to the bulb too great an extension,

by

which

THE ART

OF GLASS-BLOWING.

43

the sides

would

be rendered so thin that it

would

be liable tobe broken

by

the touch of the lightest bodies. This is the reason that,

when you

desire to obtain a large bulb,itis necessarytothicken the extremity of the tube, orto

combine many

small bulbsin one,thatit

may

possess

solidity.

In general,

when you blow

abulb withthe mouth, itisbetter tointroduce the airalittle at a time, forcing in the small portions very rapidly one afterthe other_; rather than to at-tempt to produce the whole expansion of the bulbatonce_:

you

arethen

certainofbeing able toarrestthe blowingatthepropertime.

When you

desire toproduce amoderate ex-pansion,either at theextremity or in

any

other part of a tube,

you

areenabledeasily to effect it

by

thefollowing process,which^is founded on the property possessed

by

all bodies,

and

especially

by

fluids, of expanding

when

heat-ed_; a_property which characterises air in a very highdegree. Afterhavingsealedone

end

of the tube and

drawn

outthe other, allow it to

become

cold, in orderthatit

may

bequite filledwith air

; close the

end

which has been

drawn

out,

and

pr-eventthe airwithin the tube from communicating with that at its exterior then gradually heat the part

which you

desire to have expanded,

by

turning itgently in the flame of a lamp. In a short time the softened matter is acted on

by

the tension of the air

which

is enclosed

and

heated in theinteriorof the tube_; the glass expands,

and

produces a bulb or swelling

or less extensive,

ac-44 THE

AllTOFGLASS-BLOWING.

cordingas

you

expose theglass to agreater or lesserdegree of heat.

To blow

abulbinthe middle of a tube,itis sufficient to seal itatone of itsextremities, to heat the part that

you

wish to inflate, and,

when

itis ata cherry-redheat, to

blow

inthe tube, which

must

be held horizontally and turned with both hands, of which, for the sake of greaterfacility, theleft

may

be held above

and

the right below.

If the bulb is to belarge, the matter

must

previously be thickened or accumulated, or, instead of that, a series of small bulbs first

produced,

and

thesesubsequently

blown

intoa single largerbulb,as

we

havealreadymentioned.

See pi. 1, ^fig.8.

For some

instruments, the tubes of

which must

be capillary, it is necessaryto

blow

the bulbs separately,

and

then to solder

them

to the requisite adjuncts.

The

reason of thisis,

thatit

would

be toodifficultto produce, from a very fine tube, a bulb of sufficient size and solidity toanswertheintendedpurpose.

You make

choice of a tube

which

isnot capillary, but of a sufficient diameter, very cylindrical, with equal sides,

and

tolerably substantial: it

may

^generally

be

from the twentiethtothe twelfth of an inch thickinthe glass.

You

soften

two

zones in this tube,

orlessnear to each other, according to the bulk

you

desire to give to the bulb,

and you draw

outthe meltedpart in points.

The

talent consists in well-centering

—

^that ^is ^to

say, in drawingoutthemelted tube insuch a

THE ART

OF GLASS-BLOWING.

manner

that the thin parts or points shallbe situatedexactlyinthe prolongation of tlie axis of the little portion of the original tube re-maining between them. This operation is technicallytermeddrawing

a

cylinderbetween

two

points.

The

tube so

drawn

outis exhi-bited

by

pi. 1, ^fig.4.

You

cut thesepointsat

some

distance fromthecentral or thick

parb and

seal oneend

;

you

nextcompletelysoften the littlethick tube

and expand

itintoa bulb,

by

blowing with the precautions

which

have already been described.

You must keep

the glass in continual motion, if

you

desire to

be

successful in this experiment.

Much

rapidity of

movement, and

at the

same

time lightness of touch, are requisite in the operation here described. It is termed

blowing a

bulb be-tween

two

points. PI. 1, fig. 10, exhibits a bulb

blown

between two points.

To

obtain a

round

bulb,

you

should hold the tube horizontally_; to obtain a flattened bulb,

you

shouldholditperpendicularly,with the fused extremity turned above _; toobtain a pear-shapedbulb,

you

should hold the fused extremity

downwards.

When you

areworking

upon

abulb between two points, or in the middle of a tube,

you

should hold the tube horizontally, inthe ordi-nary

manner

; but youare to pushthesoftened portion together, orto

draw

itout,accordingas

you

desire toproduce a ridge or a prolonga-tion.

When

youare at libertyto choose the point from which

you

are toblow,

you

shouldprefer.

46 THE ART

OF GLASS-BLOWING.

1st, thatwhere themoisture of the breath can betheleast prejudicial to theinstrument which

is to be

made

_; 2dly_, that

which

brings the part which is to be

expanded

nearestto your eye; 3dly, that which presents the fewest dif-ficulties in the execution.

When

bulbs are to be formed in complicated apparatus, it is

good, to reflect a little on the best

means

of effecting the object. It iseasy to understand that contrivances which

may

appear very simple on paper, present difficulties in the practical execution which often call for con-siderable

management.

—

^PIERCING.

You

firstseal thetube at oneextremity,

and

then direct the point of theflame onthepart

which you

desire to pierce.

When

the tube has acquired a reddish-ivhite heat,

you

sud-denly remove it from the flame,

and

forcibly

blow

intoit.

The

softened portion of the tube gives

way

before the pressure of the air,

and

burstsintoa hole.

You

exposethe tubeagain tothe flame,

and

borderthe edgesofthe hole.

Itisscarcely necessary to observe, that, if it be a sealed extremity which

you

desire to pierce,it isnecessaryto turn thetube

between

thefingerswhileinthefire

; butif,on the

con-trary,

you

desire topiercea holein the sideof atube,

you

should keep the glass in a fixed position, and direct the jet

upon

asingle point.

If the side of thetubeisthin,

you may

dis-pense with blowing.

The

tube is sealed

and

allow'ed to cool

; then, accurately closing the

THE ART

OF GLASS-BLOWING.

openextremitywiththe finger, oralittle wax,

you

exposeto thejetthepart

which you

^desire

tohave pierced.

When

^the ^glass^is sufficiently softened, the airenclosedinthe tubebeing

ex-panded by

the heat, and not finding at the softened part a ^sufficient resistance, bursts throughthetube,

and

thus pierces ahole.

You may

generallydispensewiththe sealing of the tube,

by

closing the ends with

wax,

or withthefingers.

There is stillanother

method

ofperforming

this operation,

which

is veryexpeditious,

and

constantly succeeds with objects which have thin sides.

Y

ou raise toareddish whiteheat alittle cylinder ofglass,ofthe diameterof the hole that

you

desire to

make, and you

^instantly applyitto thetube or globe, to which it will stronglyadhere.

You

allow the wholetocool,

and

then give the auxiliary cylinder a sharp slight

knock

; thelittle cylinderdrops^off,

and

carrieswithittheportion of thetube towhich

ithadadhered.

On

presenting the hole ^to a slightdegree of heat,

you remove

the sharp-ness ofitsedges.

When you

purpose to pierce a tube

late-rally, for the purpose of joiningto itanother tube, it is alwaysbesttopierceit

by

blowing

many

times,

and

only a littleata time,

and

withthat view, to soften the glassbut

mode-rately.

By

this

means

the tube preserves

thickness,

and

isin a betterstate to sup-portthe subsequentoperation of soldering.

Thereare circumstances in which

you

can pierce tubes

by

^forcibly ^sucking ^the ^air ^out

48 THE ART

OF GLASS-BLOWING.

them

;

and

this

method

sometimes presents advantagesthat can be turnedto

good

account.

Finally, the orifices which are produced

by

cutting otF the lateral point of atube

drawn

outat the side,

may

also be reckoned as an operationbelongingto this article.

—

BENDING.

If the tube is narrow, and the sides are prettythick, thisoperation presentsnodifficulty.

You

heat the tube, butnot too

much,

lestit

be-come

deformed_; areddish

brown

heat is suffi-cient, for at thattemperatureitgives

way

to Theslightest effort

you make

tobend it.

You

should,as

much

as possible, avoid

making

the

bend

too abrupt.

For

thispurpose,

you

heat a zoneof one or

two

inchesinextent at once,

by moving

thetube

backwards

andforwardsin the flame,

and you

take care to

bend

it very gradually.

Butifthe tubeis large,or its sidesare thin, and

you bend

it without proper precautions, the force

you employ

entirelydestroysits cylin-drical form,

and

thebentpartexhibitsnothing butadoubleflattening,

—

acanal,

or less compressed.

To

avoid this deformity it is

necessary, first, to seal the tube at one ex-tremity,

and

then, while giving it a certain curvature, to blow cautiously

by

the other ex-tremity,whichforconvenience sake should pre-viously be

drawn

out.

When

tubeshavebeen deformed

by bad

bending, asabovedescribed,

you may, by

followingthismethod,correct the fault

; that is to say,

upon

sealing one

ex-49

tremity of the deformedtube, heatingthe

flat-tenedpart,

and

blowingintothe other extremity,

yon

can withcare reproducethe roundform.

In general, that a curvature

may

be well-made,it is necessarythat the side ofthetube

In general, that a curvature

may

be well-made,it is necessarythat the side ofthetube

In document ^rt of Iag0=l^toU)(ng> (Page 62-73)

When the glass is softened, you draw out the

you

A

and

you

When

and becomes

The

no

you must

and

mould

by

and

and

Examples

and

when

employ

which you

draw

which

be-comes by

means

and

by

may

THE ART

you may,

and

assumed

You

^y

end^f

you

you must

you

you must

mouth

You may

end

some

end

drawn

and

end

be

may

You

much

you

you

Some

Water Hammer,

The

BLOWING.

The

number

philo-40 THE ART

who would make

To blow

you commence

you

more

and

you

When

made

you

and

When

you

you

mouth

moment

movement

by

you

you

become