Handicraft for boys

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.