THE ART OF WORKING GLASS
One of the most fascinating of the mechanical arts is working in glass.
One reason for this is because it is a substance so beautiful, so hard
and so fragile that it seems to the ordinary observer to be beyond the
pale of tools.
_Au contraire_, as the French say it, glass is easily worked if you
mix a little skill with the right kind of tools and it gives me much
pleasure to tell you how to do it. Further, the tools you need are few
and the material is inexpensive.
=What Glass Is.=--Before getting down to the processes by which glass
can be worked it is a good scheme to know about the substance itself.
_Hieroglyphic_[92] inscriptions on the Egyptian monuments show that
the art of working glass was practiced 4,000 years ago or before the
_Hebrew exodus_.[93] Now glass is a chemical compound, the chief
substance of which is sand.
[92] The early Egyptians carved the history of their arts on stone in
a sign language called _hieroglyphics_ from the Greek _hieros_ which
means sacred, and _glypho_ which means to carve.
[93] The departure of the Israelites from Egypt under the guidance of
Moses.
_Common glass_ is made by melting _sand_, _lime_ and _soda_ together.
Sand is formed of a chemical element called _silica_; lime is _calcium
carbonate_ and soda is _sodium carbonate_ and there you have three
chemical elements which when they are melted together make common
window glass.
Glass which contains lime is called _crown glass_ and it is this kind
which is used in making one of a pair of _achromatic_[94] lenses.
_Flint glass_ which is the kind of glass used in making the other one
of a pair of achromatic lenses contains lead instead of lime.
[94] An achromatic lens is one that is free from color.
Flint, or lead, glass melts more easily than crown, or common, glass
and this is a good pointer for you to remember when you are getting
glass for your glass blowing experiments. _Bohemian glass_, which is
largely used for chemical apparatus, is made of sand, lime and potash.
Colored glass is made by putting small quantities of various substances
into the melted glass. Thus _oxide of cobalt_[95] gives a blue color;
_oxide of chromium_, or _cupric oxide_ a green; one of the _copper
oxides_ gives it a red color, _uranium_[96] a yellow, etc.
[95] Cobalt is a metal and is usually found along with nickel.
[96] Uranium is also a metal.
=How to Cut Glass.=--About the simplest and most useful process for you
to know is how to cut glass.
To cut window glass you need (1) a _glass cutter_; (2) a drawing board
and (3) a T square. There are two kinds of glass cutters on the market
and these are (a) _steel cutters_ and (b) _diamond cutters_.
The first kind has a little steel wheel in the end, as shown at A
in Fig. 83. You can buy one for a quarter and it will serve all your
needs very well. If money is no object you can buy a glass cutter with
a diamond point such as glaziers use for about $4.00. This kind of a
glass cutter has a chip of genuine diamond in a _swivel_ end and it is
a pleasure to cut glass with one of them. It is shown at B.
[Illustration: FIG. 83. GLASS CUTTERS
A. A steel wheel glass cutter.
B. A diamond point glass cutter.]
=How to Use a Glass Cutter.=--“There are tricks in all trades but
ours,” said the carpenter as he drove in a screw with a hammer, and so
if you will dip the steel wheel cutter into some kerosene before each
cut is made you will be surprised to find how easily it cuts.
To use a diamond cutter, hold it just as you would hold a pencil and
grip the three sided part with your thumb, index and middle fingers, as
shown at C. Then place the cutter against the straight edge of your T
square, press it down firmly on the glass and draw it along evenly.
To make the right kind of a cut hold the diamond at a sharp angle, that
is, very slanting, and raise it slowly until a smooth, sound and clear
cut is made. Don’t hold it straight up and down or you will surely
spoil it, and never never cut twice over the same line.
[Illustration: FIG. 83C. THE RIGHT WAY TO HOLD A DIAMOND POINT GLASS
CUTTER]
It takes more skill to use a diamond cutter the right way than to use a
steel cutter, but a little practice will make you proficient.
[Illustration: FIG. 84. HOW TO CUT A PANE OF GLASS]
When you want to cut a sheet of glass lay it on your drawing board with
the blade of the T square on it and the head of it against the edge
of the glass as shown in Fig. 84; hold it tight and then make a good,
clean cut. You can then easily break the sheet of glass along the cut
if there is enough glass on each side of the cut to get a firm hold on.
If not put it into one of the notches on the shank of the glass cutter
and you can then easily break it off.
=How to Finish Off Glass Edges.=--When you cut a sheet of glass the
edge left by the cutter will be slightly rough. To smooth it up and
round off the corners rub it on a _whetstone_, that is any kind of a
coarse stone on which you have poured a little water. A better way is
to grind it on a grindstone if you have one.
=How to Drill Holes in Glass.=--To drill a hole through a sheet of
glass make a layer of putty ¹⁄₂ an inch thick and as large as the sheet
you are going to drill and lay the glass on it.
The idea of using the bed of putty is to allow the glass to bend a
little should you press down on the drill too hard. Take a _Morse twist
drill_ and, if you know how, grind it on a grindstone to a sharper
point than it has when you get it; the next best thing to do is to
sharpen it on your oilstone.
The best kind of a drill stock to use is an _archimedian_, or a
_reciprocating_ one, as shown at B in Fig. 11, on page 29, for then
the pressure on the glass is even in every direction. Set the drill on
the glass at the point where the hole is to be made; hold it with the
fingers of your left hand to keep it from slipping and _lubricate_ it
well with turpentine.
Work the drill at a fairly high speed and do not put too much pressure
on the drill stock or you will surely break the glass.
You will find it quite hard to drill a hole less than ¹⁄₁₆ inch in
diameter through ordinary glass because the drills will break and when
you drill a hole over ¹⁄₈ inch in diameter you will find it a slow
job because of its size, but you can drill a hole up to ¹⁄₄ inch in
diameter if you go slow and are careful.
=A Couple of Ways to Cut Glass Tubing.=--_The First Way._--A simple way
to cut, or rather break off a piece of glass tube evenly is to make a
cut all round the tube with a _three-cornered_ file[97] and you can
break it off at the line without trouble.
[97] The right name of a three cornered file is a _three square file_.
[Illustration: FIG. 85. A CUTTER FOR GLASS TUBES]
_The Second Way._--An easy and sure way to cut glass tubing off smooth
is to use a _gauge glass cutter_;[98] this is a V steel rod with a
_seat_ on one end and a steel cutting wheel on the other. The arm of
the rod holding the wheel is marked off in fractions of an inch like a
rule and a _stop_ with a set screw in it slides on this rod as shown in
Fig. 85.
[98] You can buy one of these tools of Hammacher, Schlemmer and Co.,
Fourth Ave. and 13th St., New York.
To use the cutter set the stop on the rod at the length you want to cut
the tube; then put the rod with the cutter on it in the tube and with
the seat outside; press the V rods together tight and turn it and the
tube in opposite directions when it will make a good cut and you can
break the tube in two easily.
=How to Cut Glass Disks.=--By sawing out a round board, laying it flat
on a sheet of glass and running your glass cutter around the edge of
the pattern you can cut out an approximately round disk of glass.
[Illustration: FIG. 86. A CIRCULAR GLASS CUTTER]
But to cut out a perfectly round disk you must have a _circular glass
cutter_[98a] as shown in Fig. 86. It has an adjustable cutter head
mounted on a square rod so that the head can be turned on it. The rod
is mounted on a hardwood base so that it can revolve around the latter.
[98a] You can buy one of these tools of Hammacher, Schlemmer and Co.,
Fourth Ave. and 13th St., New York.
After the cutter head is set on the rod for the size of the circle you
intend to cut hold it down on the glass by the thumb-piece. The cutter
head is then moved round in a circle and a clean cut is made after
which the edge of the disk can be smoothed up.
This circular glass cutter, which is called the _Little Beauty_, will
cut a circle 20 inches in diameter and costs about 50 cents. If you are
making a frictional electric machine this is the tool you need to cut
the glass plates with.
=How to Bend Glass Tubing.=--It is useful to know how to bend a piece
of glass tubing, especially if you are interested in chemistry and want
to set up some apparatus--in fact you should know how before you ever
start to experiment.
There are just two things you need to bend glass tubes with and these
are (1) a _Bunsen burner_[99] and (2) the _glass tubing_, both of which
you can buy of Eimer and Amend, Fourth Avenue, Cor. 18th Street, New
York.
[99] Complete instructions for making a Bunsen burner will be found
in _The Magic of Science_ by the present author and published by
Fleming H. Revell Co., New York.
_What a Bunsen Burner Is._--This is a burner in which a jet of ordinary
illuminating gas is mixed with air, the amount being regulated by a
ring which opens and closes the air holes in the burner.
A Bunsen burner makes a very hot flame because the gas in the tube
moves faster than in an ordinary burner and the oxygen in the air aids
the gas to burn. A plain Bunsen burner is shown at A, in Fig. 87. If
you have no gas in your house you can use an _alcohol lamp_[100] which
you can either buy or make for yourself.
[100] How to make an alcohol lamp out of an ink-bottle is explained
in _The Magic of Science_.
_Bending the Glass Tube._--To bend a piece of glass tube you should
have a _fish tail jet_ set in the end of the Bunsen burner to give a
wide flame like an illuminating burner as shown at B. Hold the tube
over the flame of the burner, or alcohol lamp until it is heated red
hot all along the place you want to bend it.
[Illustration: FIG. 87. KINDS OF BUNSEN BURNERS]
Now turn the tube in the flame with your fingers until it is heated
evenly all around and becomes soft; take it from the flame and quickly
but gently bend it as you will which you can do very easily. With very
little practice you will be able to make a good smooth bend just where
you want it.
=How to Blow Glass=
=To Round the Ends of a Tube.=--When you cut a tube either with a file
or a glass cutter the edge of the end will be sharp but not smooth. All
you have to do to round it is to heat it in the flame until it begins
to melt, when the glass will run and make a smooth edge.
=To Border the Ends of a Tube.=--To _border_ a tube means to spread the
edge out a little all around so that a cork can be put in easier or a
liquid poured out better.
[Illustration: FIG. 88. BORDERING THE END OF A TUBE]
Take a piece of charcoal and shave it down with your knife to form a
cone the size you want the border to be. Heat the end of the tube by
turning it in the flame until it is quite soft and then push in the
charcoal cone, as shown in Fig. 88.
=To Seal Off the End of a Tube.=--To close one end of a tube, or _seal
it off_ as it is called, heat it in a fish-tail burner just as I
explained for bending glass.
When the glass begins to get soft pull the two ends of the tube apart
until the walls of the tube are drawn together as shown at A in Fig.
89. Cut a nick in the thin solid part with a file and break it off. If
you want a closed end as shown at B heat the end of the tube you have
sealed off and press it down on a piece of iron.
[Illustration: FIG. 89. SEALING OFF THE END OF A TUBE]
[Illustration: FIG. 90. HOW TO MAKE A HOLE IN A TUBE]
=To Make a Glass Nozzle.=--In setting up chemical apparatus it very
often happens that a glass nozzle is needed. To make a nozzle seal off
a piece of glass tube as described above and by nicking it with a file
you can have the hole in the end of the tube any size you want it.
=To Make a Hole in a Tube.=--To make a hole of any size in a tube, or
_piercing_ it, as it is called, you ought to have a sharp pointed flame
and a _blow-pipe_, which is described farther on.
Cork up one end of the tube, heat the point, see A in Fig. 90, where
you want the hole and then stick the other end in your mouth and blow
gentle puffs in it until a little bulb is formed. When the bulb is cold
take a file and gently crack the thin glass and trim it away; now heat
the tube around the edge of the hole again until the glass begins to
run when a round smooth hole will be produced as shown at B.
[Illustration: FIG. 91A. WELDING TWO TUBES TOGETHER. B. MAKING A =~T~=
TUBE]
=To Join Two Tubes of the Same Size.=--Put a cork into one end of one
of the tubes and hold the other end in the flame as well as one end of
the other tube as shown at A in Fig. 91.
Let the ends of the tubes get hot enough to melt but not thicken; now
press the melted ends together hard enough to make them stick together
but not hard enough to make them form a thick ring.
[Illustration: FIG. 92A. A REGULAR BLOW-PIPE]
To make a good job you should now use a pointed flame and heat the
juncture all around red hot and blow into the open end of the tube to
spread the glass a trifle. While you are blowing keep turning the glass
in the flame to make the joint nice and smooth.
=To Join One Tube to the Side of Another One.=--First make a hole in
the side of the tube in the manner already described and then cork up
both ends; heat the tube around the hole and one end of the other tube
as shown at B, in Fig. 91. When they are soft press them together hard
enough to make a good joint.
It is a good scheme to wrap cotton around the joint while it is still
hot to _anneal_ the glass, which means to make it less brittle by
letting it get cold slowly.
[Illustration: FIG. 92B. CROSS SECTION OF A HOME MADE BLOW-PIPE]
=To Blow a Bulb on the End of a Tube.=--_How to Make a Blow-Pipe._--For
blowing bulbs on tubes, for flasks and the like, you need a regular
glassblower’s _blow-pipe_ in order to get a hotter flame than a Bunsen
burner gives.
You can buy a blow-pipe as shown at A in Fig. 92 for $1.50,[101] or you
can easily make one as follows: get a brass tube ³⁄₄ inch in diameter
and 10 inches long and drill a ¹⁄₂ inch hole in it 3 inches from one
end; fit another pipe of the same size and length at an angle of about
30 degrees to the first one; put a _stopcock_ in the latter pipe and
solder it to the first pipe over the hole as shown at B in Fig. 92.
[101] Blowpipes and bellows can be bought of Hammacher, Schlemmer and
Co., Fourth Ave. and 13th St., New York.
Next take a glass tube ¹⁄₄ inch in diameter and 14 inches long and make
a bend in it 3 inches from one end. Make a hole through a cork and push
it over the glass tube; slip the tube into the brass pipe and force the
cork into the end of the latter tight enough to hold the glass tube
exactly in the middle of it.
[Illustration: FIG. 92C. THE GLASS BLOWING ARRANGEMENT READY TO USE]
Connect the lower end of the glass tube with a rubber tube about 3
inches long to a brass tube of the same size and 8 inches long and fit
a stopcock into this pipe. This completes the burner but you want to
set the lower ends of the two tubes into and through the top of your
table so that the stopcocks are above it and the lower ends of the
tubes project below the table.
Next connect the large brass tube with a gas jet or other source of
illuminating gas and the small brass tube with a _foot blower_ or other
source of compressed air as shown at C. The blower can be an ordinary
_molders’ bellows_ which you can buy for about $1.50, or you can make
a pair, or you can buy a regular blowpipe bellows as shown at D, which
are very much better, for about $8.00.
[Illustration: FIG. 92D. A REGULAR FOOT BELLOWS]
By adjusting the mouth of the glass tube--which is the air tube--that
is, drawing it in and out of the mouth of the brass tube which is the
gas tube, and by regulating the amount of air and gas, a _pointed_
flame or a _brush_ flame, that is, a flame of large size, can be had at
the mouth of the blowpipe according to the work you are doing.
_How to Blow a Bulb._--Take a good piece of glass tube about ³⁄₄ inch
in diameter and 15 inches long; draw one end out long and thin for
about 3 inches as shown at A in Fig. 93.
[Illustration: FIG. 93. FIRST STEPS IN BLOWING A GLASS BULB
A. Drawing out the tube.
B. Forming glass rings on the tube.]
Then heat a small part of the tube in a large, or brush flame, turn the
glass in the flame all the time until it is soft and then press on both
ends to make the glass thicker at this point. Do the same thing above
the ring thus formed, and so on until you have several rings of glass
as shown at B, which are thick enough to make the sized bulb you want.
[Illustration: FIG. 93C. MAKING A THICK RING OF GLASS]
Next heat the narrower parts marked _a a a a_ and blow gently and press
gradually on the ends to make the thick rings melt and flow together
into one large ring of thick glass as shown at C; and in doing so be
mighty careful that the walls do not cave in.
Now melt and seal off the tail and heat the whole bulb in as large a
flame as you can get and at the same time turn the tube till the rings
run together. At this instant take it from the flame and, still turning
it, blow into it with a few little quick blasts until you get the size
and shape you want as shown at D.
[Illustration: FIG. 93D. LAST STEP IN BLOWING A GLASS BULB]
=How to Etch Glass.=--There are two ways to etch glass and these are
(1) with a _sand blast_ and (2) with _acid_.
_The Sand Blast Process._--The process which follows is a simplified
form of the regular sand-blast way of doing it, and with it you can
easily make a ground glass surface or etch a stencilled name or a
design on a sheet of glass.
All you need is (1) a box with a tight fitting lid 5 inches wide, 5
inches high and 10 inches long as shown at A in Fig. 94. Cut a hole in
one end, say 4¹⁄₂ × 4¹⁄₂ inches, thus leaving a margin of wood ¹⁄₂ an
inch wide all around; (2) a pound of rather coarse emery, and (3) a
pound of shot.
[Illustration: FIG. 94A. PARTS OF THE APPARATUS FOR SAND BLAST ETCHING]
Clean the surface of the glass you are going to etch with warm water
with a little soda in it, wash it off and rub it dry. Next cut a
stencil with your name on it or you can make a geometrical design by
folding a sheet of paper and cutting it out with a pair of shears. Coat
the glass with a thin layer of mucilage, lay the stencil on it and rub
it down flat. Rub the mucilage off clean in the cut out parts with a
slightly moist sponge and be sure to get it all off too.
Now cut out a piece of cloth the size of the end of the box and cut a
hole in it the exact size of the hole in the box. Lay this on the end
of the box with the hole in it, lay the glass over it and fix them all
together tight with rubber bands as shown at B in Fig. 94, or tie it up
with string. The cloth cut-out between the box and glass will prevent
the emery from sifting through.
[Illustration: FIG. 94B. SAND BLAST APPARATUS PUT TOGETHER READY FOR
ETCHING]
Put the shot and emery in the box, fasten the lid on tight and then
shake it hard up and down so that the emery and shot will strike the
surface of the glass with as much force as possible. Keep this up for
15 minutes or half an hour when the glass will be etched deep enough.
When you open the box you will find that the particles of emery have
been embedded in the lead shot and each of the latter has become a
cutting tool. This process of etching can be used for metals as well as
for glass.
_How to Make Ground Glass._--To make _ground glass_ go about it as
above described but in this case no stencil is needed.
_The Acid Process._--_Hydrofluoric acid_ is made by treating
_fluor-spar_[102] with _sulphuric acid_. The acid which is thus formed
acts on glass by eating into it and for this reason it must be kept in
either rubber, lead or platinum bottles upon which it has no effect.
In etching large surfaces the acid is not put on the glass directly;
because it eats so smoothly the effect is not striking enough; instead
the following process is used which leaves a rough surface more nearly
like that of the sand blast.
[102] Fluor-spar is _calcium fluoride_; you can buy it of Eimer
and Amend, 4th Ave. and 18th St., New York, or of the L. E. Knott
Apparatus Co., Boston, Mass.
Make a lead dish the size of the glass you want to etch and with the
sides an inch high. Put about an ounce of powdered fluor-spar into the
dish and pour enough concentrated sulphuric acid on it to make a thick
paste.
Coat the surface of the glass with paraffin, or beeswax and rosin,
and then with a steel _scriber_, or other pointed instrument scratch
on your name or the design you intend to etch, clear through to the
glass. Lay the glass with the waxed side down on the dish containing
the fluor-spar mixture, as shown at A in Fig. 95, and let it stand over
night. The vapor formed by generating hydrofluoric acid in this way
attacks the _silica_, that is the sand, of the glass with which it has
a great tendency to unite, and thus the glass disintegrates or is eaten
away.
[Illustration: FIG. 95. ETCHING GLASS WITH ACID
A. Etching a sheet of glass with fluor-spar.
B. Etching a thermometer tube with hydrofluoric acid.]
The next morning when you take off the glass, scrape off the wax and
you will find the name or design etched on it.
To etch the graduations on thermometers, burettes, etc., coat them
with wax and scratch the lines and figures on them just as described
above--but in this case you can put the hydrofluoric acid on direct as
shown at B, using a splinter of wood for the purpose.
=How to Cement Glass.=--To cement glass clean the edges or surfaces to
be fixed together with hot water in which you have put a little soda;
dry well with a clean cloth and then be careful not to let your fingers
touch the cleaned parts.
Brush over the edges or surfaces of the glass with the cement made
according to the directions which follow and press and bind the parts
together as tightly as possible.
To make the cement dissolve 2 ounces of the best _gum arabic_ in some
hot water and then add 1¹⁄₂ ounces of pulverized starch and ¹⁄₂ ounce
of sugar and stir until they are dissolved. Heat the mixture in a pot
or a tin can which sets in a larger pot or tin of water--or _water
bath_ as it is called.
When the starch gets clear take it from the fire, put in a few drops
of oil of cloves to keep the cement sweet and let it get cold, when it
should be about as thick as cream.
=A Simple Way to Frost Glass.=--Make a _saturated solution_ of _alum
water_, which means to dissolve as much alum in hot water as possible.
Lay the glass on a perfectly level table and pour on as much of the
alum water as you can without its running off and let it cool slowly,
when the alum will cover the glass with fine crystals. This is a good
substitute for ground glass.
A cheap frosting for windows can be made by dissolving Epsom salts in
hot water and then mixing it with a clear solution of gum arabic.
=Substitutes for Glass.=--There are a number of substances that can be
used instead of glass. In some cases a substitute is better than glass
but generally they are used because they are cheaper.
_Mica._--This mineral, which is also but wrongly called _isinglass_,
is found in Farther India; it is a silicate and can be split into thin
sheets; in color it ranges from colorless to a jet black and from the
transparent to the translucent. It is useful in many ways because it is
fireproof.
_Gelatine._--Gelatine is obtained from the skins, hoofs and horns
of animals. _Isinglass_ is a nearly pure gelatine and is a white,
tough, partly transparent substance which is obtained chiefly from the
air-bladders of fish.
To make sheets of either gelatine, or isinglass, dissolve some of the
finest glue, or isinglass--the latter is the best--in enough hot water
so that it will form a flexible solid sheet when it is cold.
While it is still hot strain it through a piece of cheese cloth;
this done, grease a clean sheet of glass and build up the edges with
some putty; warm the glass and pour on the gelatine to a thickness
of ¹⁄₈ inch. Now lay another greased and hot sheet of glass on top
of the gelatine and let it stay there until it is cold. The sheets
of gelatine can be given any color by adding a little aniline to the
gelatine while it is hot.
=How to Silver a Mirror.=--While it is much cheaper to buy a mirror
than it is to make one still there are times when it is useful to know
how to make one.
As you know, a mirror is a sheet of clear glass free from air bubbles
and upon the back of which is a film of silver. The silver bath is made
by mixing a weak solution of _silver nitrate with ammonium hydroxide_
until the solution is clear and then adding a little _caustic potash_
to it. This done, put in a few more drops of ammonia and finally a very
little _glycerine_.
Now float the glass on this mixture when the surface will soon be
coated with silver. When the film is thick enough take the glass from
the bath, wash the film of silver on the back of it with clean, cold
water, dry and varnish it and your mirror is done.