Harper's new monthly magazine 470, heinäkuu 1889
(Tekstiin lisätty kappaleita lukemisen helpottamiseksi. // Some paragraphs added to the original text for making reading easier.) A fragment of glass contains a wondrous wealth of curious history, of mysterious processes, of marvellous achievements. It is of most venerable pedigree, as the first substar lee cooled from the archaic molten globe was doubtless a form of glass. And the subterranean furnaces have supplied it to all the geological ages in mountains of shining obsidian, and in volcanic caverns decorated with "Pele's hair." The hugest of these cliffs of volcanic glass in Colorado gave prehistoric America a quarry of black flint-glass (the only glass known on this continent before the European invasion), from which the ancient artisans cut many utensils and ornaments. Their special use of this material was for polished mirrors, which seem to have been a favorite household property among the old Mexicans. The fact that the missionary Buddhist priest Hwui Shan presented to the Emperor of China one of these obsidian mirrors to marvel unknown to Asia) a thousand years before Columbus, with a surprising story of long travels and strange countries, is one of the chief evidences of the Chinese discovery of America.
The commonest miracle of modern civilization is glass, and (along with steel, steam, and electricity) it may fairly be esteemed a distinctive characteristic of our age. The ancients knew it chiefly as a precious material for ornament. America was entirely destitute of it until the seventeenth century. But it is an omnipresent necessity in modern life. Besides the inestimable value of a cheap material through which the sun's rays are strained from the unwelcome elements for our houses, who can reckon the domestic conveniences of glass? Science also is abjectly dependent. upon it. The commonest utensils of the chemist and physicist must be made of the unique substance, which is transparent, rustles, and incombustible. Electricity would be an untamable monster without glass to control it. The boundless enchantments of the infinitely great in astronomy and of the infinitely little in microscopy are opened through its magic convex portal.
Chemically speaking, glass is a fused combination of silicates. In other words, it is a melted mixture of sand with two oxides from a group of four—soda, potash, lime, lead. The other ingredients found in glass, as manganese, tin, arsenic, zinc, iron, etc., are coloring matters, or impurities, or correctives of impurities. It is usually named from the principal base. The ancient glass was a "soda glass," Bohemian white and English flint glass are "potash glass," cheap table-ware is "lime glass," and optical goods are "lead glass." But as every true glass contains at least two bases united to the silica, a more accurate method designates the different kinds of glass by the two principal bases. Thus, window-glass is known as a lime-soda glass, flint glass as a lead potassium glass, Bohemian glass as a potassiumlime glass, etc.
The one staple element of all glass—silica—must first be pure and minutely pulverized. The Chinese, like some of the ancients, get a fine quality of glass by pounding quartz crystals into powder. The best English glass was formerly made from flints calcined and ground, and was therefore named flint-glass. Bohemian glass is still made almost entirely from pulverized quartz rock. But the prevailing custom now is to use the silica which nature has broken and sorted in purest sand. Berkshire County, Massachusetts, supplies the New England factories with their sand. Juniata County, Pennsylvania, and Hancock County, West Virginia, supply Pittsburgh and Wheeling. The plate-glass works of Crystal City, Missouri, find their fine material at their doors, and the New Jersey sandbanks furnish the glass establishments of New Jersey and eastern Pennsylvania.
The numerous forms of glass may be best grouped in four classes, in this order:
I. Window-glass (a silicate of lime and soda or potash) is blown in two very different ways. The usual method produces "cylinder" or "sheet glass," which fills most windows. Another style of manipulation produces "crown-glass" for more lustrous and expensive glazing. The latter is no longer made in this country, and is sparingly made in Europe.
II. Plate-glass (the purest silicate of lime and soda or potash) is cast upon a. table and rolled into sheets, making the richest and largest material for windows and mirrors.
III. Green glass is the coarse "bottle glass," used chiefly for cheap bottles. It is a crude silicate of lime and soda, and obtains its green color from the iron present as an impurity in the sand.
IV. Flint-glass includes the great bulk of decorative and useful articles both blown and pressed. Its composition varies with its grade. Its peculiar brilliancy is derived from lead, which ingredient distinguishes it from all other glass. The true English flint-glass, which is the same as the French "crystal," is a silicate of potash and lead. It is very heavy, rings like metal, and is the choicest material for table and cut ware and optical purposes. When the proportion of lead is increased it becomes "stram," from which artificial gems are made. Bohemian glass is a lime glass variety of flint, like American "crystal glass," from which most of the household goods are made—dishes, chimneys, shades, bottles, vases, inkstands, etc.
Each of these four kinds of glass is produced in a peculiar establishment where generally nothing else is made.
Before we watch the glass magicians at their work we must look at the furnaces and melting-pots. The melting furnace is the backbone of the establishment. In this the rough ingredients are converted by intense heat into molten glass or "metal," for the workmen to shape as they please.
The form of this furnace is either circular or rectangular, according to the kind of glass to be produced and the fuel used. Flint glass furnaces are usually round, taking the form of a conical kiln, which is surmounted by a mammoth chimney. At its base are from eight to twelve crucibles ranged in a circle about the central grate fire, which is supplied with coal fuel and with air from underground approaches. This is the traditional furnace for melting. It receives the covered crucibles through large arches on every side, which are closed by fire-bricks and clay, concealing all but the openings of the crucibles. This form is modified to a rectangular shape for window, plate, and bottle glass, with doors at each end. The open pots are put in through these doors, and their contents withdrawn through openings in two rows at the sides. Gas is rapidly displacing other fuel in this industry, and it works best in square or oblong walls, with a plain floor in place of the grate. Entering at each end, it is mixed with air which has become heated by passing through chambers in the fire-brick arches that support the furnace, on the plan of the Bunsen burner, producing an intense heat, which can be perfectly controlled. In all cases a well is built under the furnace to receive the molten glass that may escape from a broken pot.
The melting-pots for window, plate, or green glass are open truncated cones, the smallest diameter and thickest structure being at the bottom. For flint-glass the crucibles, or "monkeypots," are usually oval cylinders with a rounded covering opening only on the top of one side. The pots demand for their manufacture the most tedious and exacting work of the entire industry, as the slightest flaw in structure or material is sufficient to waste all their precious contents. They are a costly item in the manufacture. As each pot, is worth from $40 to $100. and they are delicate creatures requiring most fastidious handling. Front the digging of the clay until it is refined, mixed, kneaded, and built into pots, and these thoroughly dried, heated, and set in place, months of careful nurture are required. The average life of an open pot in its furnace home is only about seven weeks, and the most hardy monkey" seldom survives three months. Most of them die prematurely from invisible weakness of constitution, from bad treatment in the pot arch, or from being "starved," that is, exposed to a current of cold air through the attendants neglect. The pots ace made of fire-clay obtained at St.. Louis or imported from Germany or England. and mixed in varying proportions of raw and burned clay and pieces of the broken pots called "pot shells," freed from glass and ground fine. The pulverized mixture is moistened to a doughy consistency in great leadlined bins. Daily for a month it is kneaded by the bare feet of a workman to render it tough as putty. With utmost care it is then built by hand in a room that is constantly warm and moist. First the bottom is formed four inches thick. Then the sides are gradually shaped from the sticky material, through a period of six weeks, tapering to a thickness at the top of three inches. The ordinary size is 34 inches high and 424. inches wide, holding about 1500 pounds of melted glass. When finished the pots stand from two months to a year—the longer the better—in the potroom to dry. Then they are baked in the annealing oven or a small furnace, where the temperature gradually rises to that of the melting furnace, and are transferred at once to their posts of duty, to be glazed inside with melted glass, imprisoned with their backs to the fire and their gaping mouths to the outer world, ready to be filled with the mixture to be melted. But in spite of the best pains a pot frequently breaks after a brief trial.
As soon as a crack is seen the furnace must be slacked, and the casement of brick and clay battered down, with screens of sheetiron to shield the attacking party from the glare and heat. Only after a siege of several hours are the dozen men able to extract the redhot monster from his cavern of fire, and drag him on a truck outdoors, while all faces are covered from the blinding intensity of his glow. Such a scene provides upparalleled facilities for "hot pot" imaginations, and might even assist Dante's conception of an orthodox Inferno.
But there are many serious disadvantages attached to the use of pots either open or covered. While the melted glass is being worked the furnace must be cooled, and when the material is exhausted the men must wait ten or twelve hours for another batch to be melted. The cracking of a pot stops everything for a day until the pot is removed, another built into its place, and its contents fused. These difficulties, and also the annoyance of sulphur and soot from coal fuel, are entirely removed by the "tank furnaces" heated by gas, which are remodelling glass-making. The original and staple tank furnace bears the name of its inventor, Siemens, and is heated from the sides by his wellknown regenerative gas system. In place of the melting-pots there is a tank made of the same material as the pots, in blocks, which occupies the whole bed of the furnace, and is divided into three compartments separated by floating partitions. At the rear side of the furnace is the melting compartment, which is fed with frequent charges of raw material. As this melts it sinks to the bottom, and through an opening at the base of the partition passes to the refining compartment. Here it finds a higher temperature, and as it becomes purified it flows out below the next partition to the gathering compartment. This last is exposed to a lower heat than the other two, and permits the melted glass to thicken for the blower's use. The floating partitions are dispensed with in a later improvement, in which refining vessels float upon the sea of glass and gather the molten material from the lowest depth, raising it to the surface to be refined in another compart men t, when ce it flows into the workingout compartment.
The working furnaces, of which there are several to every melting furnace, are small blastfurnaces, usually heated in this country by benzine, each providing a number of openings directly into the flames. A spectator sees at once the appropriateness of their name—"glory-holes." In these the workman resof tens the glass as he completes the various small objects.
The annealing oven is a long, low, rectangular chamber through which the finished products slowly pass in shallow trays from an intense heat to the ordinary temperature. At one end of it the red and blue flames dash into their receptionroom above the objects which are entered there for tempering, lining the roof with long trails of fire, and hastening through the course that leads them to the tall chimney. At the other end the products of the factory are removed into the cool air.
For window-glass the raw material or "batch" contains 30 to 36 per cent. of raw limestone, 35 to 42 per cent. of sulphate of soda, 1½ to 2½ per cent. pulverized charcoal, to each 100 parts of sand. These are thoroughly ground and mixed together. The relative amounts of the ingredients are alike in no two establishments.
When the furnace has been brought to the proper temperature the pots are filled with the mixture, and as soon as this is melted down, depending on the size of the pots and the heat of the furnace, a second filling is put in, and lastly a third, which generally fills the pot; in case it does not, a few shovelfuls of broken glass called "cullet" are added. The entire melting requires about sixteen hours, and is carefully watched by the master molter, who urges the furnaces to their utmost intensity, and is on the alert for the signs which indicate when the metal is ready. The heat is then lowered to make the glass less fluid, and now the workmen begin their wonders.
They are a muscular set, and the hot surroundings compel them to dispense with all superfluous clothing. Each workman is trained to one small part of the process, and does nothing else. In making a pane of window-glass, for instance, the labor is divided among four men, the gatherer, the blower, the flattener, and the cutter. The gatherer puts between his teeth the wooden plug by which he holds in position a rough mask to screen his face from the furnace. Then lie seizes the blowpipe, a simple wroughtiron tube flared on one end, and starts the "journey," as the working of the glass is called. He dips the flared end of the pipe into the pot, and turning it carefully, covers it with glass. When it is slightly cooled he repeats the operation, and then shapes the metal into a symmetrical oval in a mould. He again dips the pipe into the metal, when enough adheres to that already on the pipe for a cylinder of the ordinary dimensions. When the glass is to be of double thickness, the metal must be gathered four or five times, and weighs from thirty to forty pounds.
The final dip requires the greatest skill, for the plastic ball must be got into a homogeneous and symmetrical shape before it leaves the furnace. This the gatherer accomplishes by resting his pipe on a convenient fulcrum and rapidly revolving the mass in the fiery pot until the last glass completely overlaps the earlier lump. Now he takes the great glaring ball to an iron mould, and with a few dexterous turns fashions it into a pear shape. When this is done the gatherer's duty is ended, and lie hands the pipe and glass over to the blower.
The French and Belgian blowing furnaces are combined with the melting furnace, but in England and America they are separate, being constructed with a series of openings through which the blower may insert his material into an intensely hot chamber. The gas supplying the heat is burned directly under the blow-holes, being mixed with air from fire-clay shafts surrounding the burners on the plan of the Bunsen burner. Slabs of fire•brick distribute the massive heat into hundreds of small jets, which cannot touch the glass.
The blower's skill is the most marvellous part of the fascinating series of transformations witnessed in the glasshouse, conjuring the glaring globe (a gigantic dragon's eye) by artful whispers into a sheet of solid transparency. He takes the pipe from the gatherer, with the great pearshaped mass still resting in the mould, and blows a huge bubble of air into it. Then, alternately blowing and manipulating, he enlarges the bubble and shapes the mass into the form of a great decanter with a short neck and very thick bottom. The thinnest part of the glass next the pipe quickly hardens into the fixed foundation from which the soft hot remainder is to grow into a cylinder of the same diameter. In front of each blow-hole is a long narrow platform at right angles to the furnace, spanning a deep pit. This is a blower's post. Standing there, he swings the swelling bulb into the abyss, like an enormous hollow pendulum carved from flame, coaxing it to expand with frequent timely blowings. When it stiffens disobediently he rests the pipe on a handy prop, and softens the refractory end in the furnace. When the glass flows too freely he tosses the cylinder into the air until it settles together in proper consistency. Blowing, swinging, and heating, lie extends the bubble to nearly his own length, and the glass becomes a roundtipped cylinder resembling the hotwater reservoir attached to kitchen ranges.
As the cylinder is a foot in diameter and five feet long, and the tube is as much longer, the most delicate skill must be coupled with steady muscle for this work. The blower's work is the most difficult and profitable part of the entire trade. For large cylinders furnishing a pane 44 to 70 inches of double thickness the labor is so severe that few men are equal to it. When the cylinder is comparatively cool the blower holds the end in the furnace, blows into the pipe, and quickly covers the mouthpiece with his hand. A slight report follows. The end has softened with the heat, and the expanding air within has blown an escape through the glass. Still keeping the glass in the furnace, he revolves it until the centrifugal force extends the hole larger and larger, and at last to the size of the cylinder. Now lie removes it from the furnace, and suspends it in the pit, until the soft edge cools to a cherry red. Then an assistant carries it off, and the blower's work is done. After a monient's rest be receives another pipe with an embryo cylinder in the form of a plastic mass, and repeats the same process for ten hours.
When the cylinder is finished and placed on the "horse," the pipe is detached from it by touching the neck with a cold iron. To cu I. oft the remaining portion of the neck the cylinder is encircled by a thread of hot glass and touched with a cold iron, after which it is cracked open lengthwise by passing a redhot iron along its inner surface.
It, is next taken to be flattened. The flattening oven has a turntable carrying four stones about 40 by 80 inches, made of fire-clay. After a preliminary warming the flattener places the cylinder upon the stone before him, and as soon as it is sufflciently warm to yield under its own weight he opens it, when it looks somewhat like a rumpled sheet of paper. lie smooths it out by passing a wooden block over it, the wheel is turned, and the stone with its sheet passes into the cooling oven.
When comes its turn to be piled, the flattener lifts the glass off the stone with a longpronged fork and puts it on a car at the mouth of the annealing tunnel, called a "leer," or lays it on the rods in case the more advantageous "rod leer" is used. By the gradual and slow loss of heat in passing through the "leer" it is tempered for service.
It is in the flattening oven that cylinder glass loses its beautiful fire surface; for when first blown it has all the brilliancy of its elder and more aristocratic sister crown-glass. But the fire of the oven dulls it, and the flattener, if not careful, burrs it and scratches it, and after it leaves his hands all its first glow is gone. The American manufacturer can melt his glass as thoroughly as it can be melted by his great foreign competitors of Belgium and England, the gatherer can gather it as well, the blower can blow it as well, but until the system of flattening be changed, and more painstaking care be given to the industry from masters down through all time ranks of workmen in the factory, foreign glass must hold its own in the judgment of architects against that portion of the American product it supplants.
In all the branches of this work the advantages of gaseous fuel are an important element. The old glass made by coal was much inferior to the gasmade product, being coated with smoke and a white deposit of sulphur which could not be wholly cleansed. But gas produces a surface brilliant and clear, and by the employment of this fuel American glass-makers have in the last ten years greatly improved their product, and in many cases have reason to be proud of the excellence of their glass. While this is due partly to Yankee ingenuity in improving processes, it is owing chiefly to natural or artificial gas, providing a greater heat than coal, a better fusion, with no soot or cinders, and capable of being used on a gigantic scale. And the gas is so much cheaper than coal that many Western works have withdrawn from the competition, or have adopted manufactured gas.
Crown-glass is of far less importance now than its young rival, sheet glass, though once it held the highest place. It. is much more brilliant, but the panes are small and of unequal thickness. It is made in but few establishments, and chiefly for ornamental use.
The difference of manufacture consists only in the manipulation of the same molten material. When the glass is gathered on the end of the blowpipe it is rolled on a metal or stone table ("the marver") until it is shaped into a cone, the extremity of which, called the "bullion-point," makes the decorative bull's-eye used in mosaic windows. The workman blows the glass into a globe, and then flattens the under side of it, keeping the bullion point in the centre. He rests the pipe on two horizontal supports, while another workman attaches a warm cup of glass, carried upon his iron rod (known as a "pontee," or "punty"), to the bullionpoint.. Now the glass globe is fastened to two bars, the punty and the blowpipe. The blower touches the glass next to his pipe with a cold iron and quickly strikes it, severing the blow pipe from its charge and giving the glass over to the pun ty. Where it left the blowpipe is a round opening, or, as the worker calls it, "a nose," which is inserted into the furnace. By rapid revolution of the punty and reheating, the opening grows larger and larger until the glass takes the crown shape from which it is named.
As the heat and centrifugal force continue, the crown opens out to a circular plate or "table," which is constantly held out flat by swift whirling until it is laid on a bed. Shears detach the punty from the bull's-eye, and the table goes into the annealing oven for one or two days. The diameter of such a plate varies from a few inches to the extreme size of six feet. After annealing, the disk is cut by a diamond into square panes, but the bull's-eye in the centre compels them to be small, and this disadvantage is not commercially atoned for by the admirable brilliancy of crown-glass. Recently the bull's-eye plates have become popular to decorate artistic houses. Frequently the circular tables" are used just as they come from the oven, tinted in amber or opalescent shades.
Colored glass windows are produced in many ways. The terms "colored," "painted," "stained," and "mosaic," are commonly used synonymously, but they refer to very different processes. Plain colored glass has neither paint nor stain, being dyed in the pot. Flashed glass, such as is used for lanterns, signs, and names of streets in street cars, is made the same as window-glass except that the clear is coated at the start with a colored layer by being dipped into a pot of very deep color. This thin envelope is cut through to the plain glass by the sand blast or acid to make the lettering in signs. Painted glass gets its color from enamels fused to the surface. Stained glass is produced by soluble metal oxides applied with a brush and attached by heat. Mosaic is a mass of fragments bound together by strips of grooved lead. Often all these methods of combining colors are joined in one window, but the best. practice now relies chiefly upon mosaic. Mosaic glass has rapidly improved in the past century, becoming less and less conventional.
The old style of grouping simply red, blue, and yellow has given way to a broad range of color, and has elevated mosaic window work to a high rank among the fine arts. Great advantage is gained also by mixing several colors while the glass is still plastic, skilfully welding various tints in a mottled plate. The last few years have also introduced opalescence into all varieties of colored glass work. The "jewels" cut from pieces of a rich colored glass add effectively to the brilliancy of recent designs.
The coloring materials most largely used are iron, manganese, copper, cobalt, and gold, generally oxides. The same metal produces several colors at different temperatures. From iron all the colors of the spectrum may be produced, and in the order of their position in the spectrum, but its commonest effects are green and orange. Manganese, which is used so frequently as a decolorizer as to be called "glass-makers' soap," is also the staple material for pink or purple. If the glass containing it is left too long in the furnace it becomes pale brown, then yellow, and finally green. Copper produces the reds of cheap glass, and by raising the temperature the result is purple and then blue. Cobalt gives blue or black. The finest rubies and violets come from gold. One part of gold will give a full rich color to 1000 parts of glass, and the color can be modified from amber through a gorgeous series of reds to ruby. Carbon (powdered cannelcoal) is used for cheap black and amber bottles. Opalescent ware has many materials for coloring, as tin, arsenic, cryolite. It is by skilfully using the effect of heat in varying colors that some of the handsomest effects of modern fancy glass are accomplished.
All glass into which manganese enters in even the slightest quantity undergoes a change of hue through the operation of sunlight. The windows in some of the old houses in Beacon Street, Boston, that are so conspicuous for their soft amethystine tints, are beautiful and striking examples of molecular changes that the years of sunlight have wrought on the ingredients of the glass. And the chances are that like changes will take place in all the windows of today, but time will only mellow and soften them.
Plain colored glass is blown like ordinary window-glass. But for mosaic glass, in which a rough opaque surface is desired, to produce rich color effects the glass is cast, like plate-glass, except that the molten metal is dipped out in small iron ladles. When several colors are desired in one sheet, the different masses are mixed with a copper trowel. Three or four colors may be manipulated thus by an artist with marvellous success. Particularly admirable are the sky effects obtained by blue and white, and the drapery lines made in casting by streaks of color. In the studio the colored drawing of the design is enlarged to actual size, and divided by black lines where the lead strips are to fasten the pieces together. Extreme delicacy of judgment is required to bring together precisely the combinations requisite to produce the artistic effect of landscape, drapery, and figure, as the entire effect is made without paint or stain except monochrome shading. Mr. Louis C. Tiffany has brought the art. of making opalescent. glass to the highest perfection it has yet attained. A remarkable illustration of his success is the memorial window for St. Paul's Church, Milwaukee, Wisconsin –the largest opalescent window in the world—reproducing Dore's painting "Christ leaving the Proetorium."
Plate-glass has only recently been attempted in this country, and there are but four large establishments making it, but they produce enormous quantities, that compete in quality and price with the best European grades. The largest plate-glass plant is at Creighton, twenty miles north of Pittsburgh, and near the famous gas district of Tarenton. It is marvellously equipped for prodigious results. The glass is a double silicate of lime and soda, like sheet and crown glam, but melted in large open kettles, instead of monkeypots, which are placed on frames behind fire-clay doors. When the fusion is complete the door is opened, and a gigantic twopronged fork, mounted on wheels, enters the furnace, grasping the kettle by depressions on each side of it. It brings out the glowing gallons of molten glass to a low truck, which carries it to the casting table. At Creighton the casting house, containing furnaces, tables, and annealing ovens, is 65 by 150 feet, four times as large as the famous St.–Gobelain Halle in France, and nearly twice the size of the British works at Ravenhead. There are two iron casting tables, seven inches thick, nineteen feet long, and fourteen feet wide. They run on tracks which reach every furnace and annealing oven. The table is brought as near as possible to the furnace, and over it the kettle of melted glass is hoisted by a crane, and poured in a glaring golden mass. A heavy iron roller thirty inches thick and fifteen feet long passes over it, spreading the glass into a uniform thickness, determined by the iron strips at each side of the table upon which the roller moves. At once the plate is pushed into the annealing oven, where it remains several days. It conies out rough and uneven, good only for skylights and floors, where strength is required without transparency. But most of it is ground and polished.
The plates are made fast by plaster of Paris to large rotary platforms, which revolve so that. the entire surface of the glass is covered at each rotation by the disks of rotary grinding engines. These remove the general roughness by means of common river sand dredged from the Alleghany. Three million bushels of sand are used every year for this purpose. Finer smoothing is effected by emery of different grades, and the last polishing is done by rouge (calcined sulphate of iron). These operations remove forty per cent. of the original plate, leaving it from onefourth to threeeighths of an inch thick. The Creighton works produce 100,000 square feet of glass every month. Natural gas is the only fuel, taking the place of 34)00 bushels of coal daily. These figures may dispel the mistaken opinion that we depend mainly upon France and Belgium for our supply of plate-glass. A part of the glass at Creighton is used for mirrors. The unpolished glass called "rolled plate," which is fluted in fine lines or indented in ornamental patterns for obscure lights in door panels, partitions. etc., is made by casting the plate-glass upon an engraved table.
Green glass, or "bottle glass," is used only for the cheaper grades of bottles. The amber glass also used for common bottles is colored from the same material by the addition of a trifling quantity of carbon. Fine bottles are made only from flint-glass, but the green glass work is an important and distinct trade, involving little of the skill and nicety required by other grades. It is conducted in America most extensively and successfully near Philadelphia. Much of the sand of southern New Jersey is rutiicienthy line to make excellent bottles. The bottle blower's work is quite simple. He gathers the molten glass on a blowpipe in the quantity desired for a bottle, puffs a bubble into it, drops the red lump into an iron mould, which a small boy closes together, and blows the glass into its fixed shape, with whatever ornament or lettering is cut in the mould. The sharp broken mouth is then rounded in the "glory-hole," and the bottle goes to the annealing chamber.
Flint-glass is the general term for all the multiform utensils and ornaments (apart from windows and dark bottles) which make glass an omnipresent blessing, in modern life. The distinctive peculiarity of flint-glass is the presence in it of lead, which imparts a brilliancy unlike that of most other glass. The lacklustre surface of all the old objects of glass made before the English invention of a lead formula is noticeable. Lead oxide was originally used only in most expensive glass prepared from calcined flints. But gradually it has crept into many grades, down to the most common material for household and fancy wares and for all transparent bottles, giving them all a finer lustre than was otherwise obtained until the recent invention of lime glass. And the costliest of all glass, that used for optical lenses and imitation gems, still gains its extraordinary weight and refractive power from lead. The honors of skill in flint-glass production are broadly divided among the nations, England taking the lead in the crystal or purest flint glass used for cutting; Italy (Venice) in colored designs more brilliant than any made in the days of the republic, when flint-glass was not known; Switzerland in imitation gems; Germany in cheap vases; France in lens disks; and America in pressed glass and cheap table-ware. Recently a cheaper flint-glass has been introduced into American pressed ware, in which lime is substituted for lead, yet which retains much of the lustre and clearness of lead flint.
Flint-glass is either blown, moulded, or pressed, and frequently all three methods may be seen together in the same establishment. A flint-glass factory is a most entertaining medley of marvels. As you enter the great building that surrounds the huge chimney the first impression is that you are in a human anthill rumbling with inordinate activity. Or perhaps the sensation is better described as a plunge into a purgatorial chamber of industrious demons. In the centre the openings in the gigantic furnace dazzle you like glaring eyes front a soul of fire; but the glow comes really from molten glass in the dozen "monkeypots" about the blaze. Scores of workers, boys, youths, and men, throng in restless confusion. It looks as if every one were running about on some impish deed of his own fancy. But stand still and watch closely, and you will see it is all a great system of human clock work, each movement fitting nicely into the whole effect. The men at the furnace, who seemed at first to be devils thrusting pitchforks into the blazing depths to toast their victims, are only gathering metal on their punties. When a sufficiently large lump has been collected the man wanders off with it. You think he will certainly burn some one with that burning ball of fire, they are all bustling about hint so incessantly. But follow him carefully and you see him silently hand the tube to an older man, who blows the glass into a large globe, and sits down to play with it at a bench which has a horizontal iron bar on each side of him to roll the tube on. Back and forth he rolls it like atoy,and the glass keeps curiously changing its shape. He has made a hole in the globe and has enlarged it into a symmetrical opening, and now the glass is cooled so that he can do nothing more. Will anybody in all that hurrying crowd help him? Instantly a young man appears, and without a word he holds up to the cool glass his long tube with a disk of redhot glass on the end, which fastens to it. The man at the bench scratches the globe, jars it, and it leaves his bar. Off the other man runs with it to the "glory-hole," where the broken end is quickly heated again into softness. Then he hurries back with it to the bench man, who renews his play. A couple of minutes more and suddenly you perceive that he has made a perfect lamp shade, which a stroke detaches from the iron rod into a small bed of sand. A small boy carries it off on a stick to the annealing furnace, and now the gatherer is on hand again with a fresh lump of metal to begin the process again. Turn to the next man sitting at his work, and you notice him finishing a smaller charge into a lamp chimney, shaping the top by a mould. Here is a man amusing himself with a small bunch of soft glass on his rod. You are sure he can have no serious purpose in turning and bending it into those ridiculous shapes. Quickly a boy seizes it from him, and you cannot trace him. It has gone over to a fancy vase, where it was needed to complete the ornament. So each bench has its own little task of skill, and keeps repeating it over and over, and each boy of the multitude (there are two or more to every man) has his own particular duties. He pops up always in the moment and place where he is needed.
All the workers are busy as their wits can make them, for they work by the piece, and the number of things made determines their wages. They are grouped into sets or "shops" of three or four, who work together and share profits together on a wellunderstood grade of division. Generally four constitute a shop, the most skilful workman (the blower) at the head, the gatherer (a young fellow) next, and two boys, one handling moulds or tools, and the other carrying the products to the annealing oven. The only way to learn the glass trade is through long apprenticeship in these four stages. And no apprentice is permitted to enter the full privilege and wages of a master-workman without the consent of the order. By this severe means of apprenticeship the glass-workers keep the skill of their trade in their own control, much like the old Venetian artisans, and practically dictate their own prices to employers.
But let us look at the other sights in this house of magic. Here they are making small druggists' bottles, called "prescriptions." The blower has a narrow light tube, and adroitly gathers a small red lump on the end. He rolls it into a cylindrical shape, blows it out into a small pouch, and puts it into the iron mould held ready for it by a boy. The mould closes together around it, and the man blows the glass till it fills the mould, and the remainder swells out into a thin shell at the top and bursts with a puff. While it is cooling in its mould a second one is being blown into another mould. The small boy has all he can do to empty the moulds and close them over the red newcomers. Another boy finishes the bottles by holding the ragged necks into the furnace to be rounded evenly, and carries them to the annealing "leer." A very dexterous man is able to blow 400 dozen small bottles a day. Most of the manifold formsof glass are formed in analogous processes by the blower's breath, not only bottles, but decanters, goblets, pitchers. These, however, are all cheaper grades, as the moulds prevent the peculiar polish which comes from working in the air.
Let us watch another workman who is rolling on a marver his freshly gathered lump of soft glass. A little puff of air blows it into a bulb which he swings out into longer shape. From this lie is going to make a goblet, though lie might as easily produce from it a pitcher, a bottle, or a chimney. The bulb is swelled out to the size desired for the bowl. He attaches a small red lump to the bottom of the bowl and draws it out into a stem. Another man has cast a bellshaped piece, and this is fastened to the stem for the base of the goblet, then flattened into proper shape in a mould. The blowpipe is detached from the upper half of the bowl, which is trimmed by shears. Finally the end is rounded in the furnace. The more expensive goblet has the stem drawn out from the original bulb and the base blown separately like a tiny disk of crown-glass. A pitcher has its body formed first, either by being blown into a mould or slowly developed from a bud by patient fingers. The handle is added separately as a lump attached to one end, then drawn out to the desired length, cut off, and attached. All the tools are extremely simple, demanding great cleverness of handling.
The most entrancing corner of a flint-glass establishment is the part where colored glass is worked into some of its myriad combinations. Many flint-glass furnaces have several different colors of glass melted continually alongside of the transparent staple to supply material for fancy wares. To describe all the beautiful combinations of color and form and their method of growth would be impossible. Frequently two or three layers of different color are combined, as if cemented together, making a basis for cameo engraving or fancy manipulation. This is done by dipping successively into the different pots, skilfully distributing each extra color evenly over the central one, and then blowing them all as one into the desired shape. The decorative gas globes with knobs or fancy patterns in a single color of glass are made by blowing the bulb into a mould which gives the ornamental form, and then finishing the two openings by hand. The interlacing of colored stripes requires a machine which winds threads of glass in opposite directions upon any surface. The amber ware, so popular of late, shaded into ruby on one end, is a curious product which was long held as a precious alchemistic secret by the glass trade. The amber color is produced from common flint-glass by mixing a fine solution of gold with the "metal." When the amber glass becomes cold and is reheated it turns to a ruby red. Therefore, by exposing one end of the vase or goblet of amber glass to the flame, that extremity is changed to a rich red color, fading back into the unaltered amber.
Yonder two men have a mass of fiery glass as large as their heads between them, each supporting it by a long rod. They carry it off to one corner and walk away from each other, drawing it out into a long rope, which you expect to see the boys jump over. But they soberly keep to their work, and when it is all drawn out they lay it down in a wooden trough, and cut it off into bars of even length. These are going to a glass button factory, where they are reheated and pressed by moulds into the dressmaker's materials. Glass tubes are drawn out in the same way from a mass which has been blown hollow.
In another direction you notice one of the pressing machines which American invention has added to the improvement of the glass trade. The plastic glass is dropped into a castiron mould, and forced by handpressure into the fixed shape within. In this way most of the cheapest glass objects of common hues are made—dishes, inkstands, lamps, etc. Imitation cut glass is one of the common products of the pressingmachine. But it can always be distinguished from the genuine expensive article by the inferior lustre and the unavoidable rounded edges. In decanters and cruets the deception is heightened by using real cut-glass stoppers. Sometimes the facets of pressed glass are cut, but they always lack the brilliancy of true cut glass.
The most brilliant forms of transparent flint-glass, or "crystal," are those blown into the gineral shape desired — dishes, globes, bottles, etc.—and cut into groups of glistening facets. This cut glass is slowly ground into its angular patterns on stone wheels on which moist sand drips continually from above. The polishing is completed by finer grains of sand, and by wooden wheels supplied with emery, and finally putty powder. These grindingmills also remove the punty marks on tumblers, wineglasses, etc. "Ground glass" is made by touching time surface to one of these wheels, or by the application of sand in a blast or with water. The roughing of bottleneck interiors is done by iron tools fixed on a lathe and moistened with sand and water. Copper disks engrave the fancy designs that ornament fine goblets and shades. Etched or embossed glass is made by submitting the glass to the biting of hydrofluoric acid, the only acid which will affect glass, the unetched portion of the glass being protected by a coating of wax or some pitchy substance.
The best wages in the glass industry are received by the window-glass blowers, sometimes reaching twelve dollars per day. The master-melters rank next, though they seldom get more than half that amount. From these earnings the prices slope down to the small tending boys, who are psid thirty cents for ten hours' work. The blower's occupation is laborious, but not unhealthful. He works eight or ten hours at a stretch, finishing one melt of glass. There are four or five melts every week, each requiring sixteen hours to fuse, ten hours of blowing, and ten hours of flattening. The work is always by the piece, and in teams or in "shops," each composed of one master-workman and several younger assistants. There are in operation about 160 furnaces, at which there are employed about 4000 blowers, gatherers. flatteners, and cutters. They are bound together by a union that dictates. the quantity each workman may make, the number of apprentices that may be taken (generally not more than two to a furnace), that prohibits any foreign workman from getting a place in the factories, or any glass from being made in the months of July and August. The average time they have worked in the last four years has been less than eight months and a half. Much of the time lost has been spent in strikes or disputes with the manufacturers about wages.
Our thermometers come chiefly from abroad. The common mercurial one passes through the most difficult process. It is made upon the principle of quickly drawing out a hollow sphere into a thin tube which keeps all the character of its original. The lump of glass is blown hollow. An assistant fastens his punty to the round end and pulls the lump into a short thick tube, which is pressed into an elliptical shape. The flattened tube is then coated with another portion of melted glass, and it is rolled on an iron slab until a cylindrical exterior is formed around the flattened bore, leaving an elliptical opening within. A small batch of white glass is attached to it, and the furnace evenly distributes it over one side. Now it is a short thick cylindrical tube, white on one side. It is drawn out into a long thin tube ; but the drawing preserves exactly the first shape and proportions, merely reducing the size. The tube is cut off into the lengths required. Holding one of the pieces to a blowpipe, the workman converts the end of it into a bulb. It is then heated to expel the air, and the open end plunged into mercury. This is repeated until the mercury entirely displaces the air, when the open end is hermetically sealed. It. goes thence to the graduator, who marks on it by careful tests the scale of degrees, which are indicated by the fine flat thread of mercury against the white background.
Most of the world's beads are Venetian. In the island of Murano a thousand workmen are devoted to this branch. The first process is to draw the glass into tubes of the diameter of the proposed bead. For this purpose the glasshouse at Murano has a kind of ropewalk gallery 150 feet long. By gathering various colors from different pots and twisting them into one mass many combinations of color are made. The tubes are carefully sorted by diameters, and chipped into fragments of uniform size. These pieces are stirred in a mixture of sand and ashes, which fills the holes, and prevents the sides from closing together when they are heated. They are next placed in a kind of frying-pan, and constantly stirred over a fire until the edges are rounded into a globular form. When cool they are shaken in one set of sieves until the ashes are separated, and in another series of sieves until they are perfectly sorted by sizes. Then they are threaded by children, tied in bundles, and exported to the ends of the earth. France has long produced the "pearl beads" which in the finer forms are close imitations of pearls. They are said to have been invented by M. Jaquin in 1656. The common variety threaded for ornament is blown from glass tubes. An expert workman can blow five or six thousand globules in a day. They are lined with powdered fish scales and filled with wax. It. takes 16,000 fish to make a pound of the scaly essence of pearl. Until recently the heirs of Jaquin still carried on a large factory of these mockpearls. The best of them are blown irregular to counterfeit nature, some in pear shape, others like olives, and they easily pass for genuine.
Imitation gems formerly employed the chief attention of the highest artificers in glass. They are still the chief idea of ornamental glass in China. In the ancient and middle ages they circulated everywhere without much danger of discovery, and their formulas were held as precious secrets. Blancourt first published their compositions in 1696. Now they are common property ; and with the growth of science in the past century an expert knowledge has become widely disseminated which easily detects the paste from the real jewel, particularly as the modern false stones are less successful copies than the old glass makers produced. More study is now given to artificial gems, which are true gems, being composed of the same materials as the genuine ones, but manufactured. Mirrors are made chiefly in Europe, the cheap ones in Germany, which invented the tin amalgam in the fourteenth century, and the large expensive ones in France. The silvering table is a smooth slab of thick wood or stone fixed on a pivot so that one side may be raised, and having a frame on three sides. The slab is placed horizontally, and covered tightly with gray paper. A smooth thin sheet of tin-foil is laid on the paper, and mercury is poured on its flat surface. The plate of glass is then carefully slid into the frame. Gently it is dropped, squeezing out the superfluous mercury, which runs of in a channel and is collected below. The plate is then covered with flannel, loaded with weights, and tilted on an incline. In this position it. remains an entire day, while the mercury drips off. Then it is cautiously lifted from the frame. The amalgam has adhered to the glass, and after it has hardened for several days it is ready for use. Most of the mirrors are now made by the quicker and cheaper process of painting the plate of polished glass with a preparation of silver. They are known as "red backs." The common lookingglasses for bureaus, etc., millions of feet. of which are imported yearly, are known in commerce as German mirror plates. A German family will take home a box of ordinary window-glass, the mother and children will polish the surface of each light with rouge, and when it is done, take the glass back to the maker of the lookingglasses, and get another box.
For optical instruments the glass must be as dense as possible, as the refractive power increases with its weight. The sand is therefore mixed with large quantities of lead and potash. The melting-pot is covered with a dome roof to exclude smoke and gases. The fusing material is stirred with a fire-clay cylinder until the melting is complete, then the furnace heat is lowered, and the pots rest for a couple of hours to permit all the bubbles to rise. The gummy mass is then constantly stirred, while the temperature declines so low that at last stirring becomes very difficult. Then the cylinder is withdrawn, all the openings of the furnace are stopped, and the crucible and glass gradually cool. This requires a week. The pot is taken out and carefully broken away from the great lump of flint-glass. Parallel faces on its sides are ground and polished to locate the interior blemishes, which determine how the glass shall be cut to the best advantage. It is then tediously cut, ground, and polished. For large lenses the glass is cast into a round flat plate. Repeated trials are necessary before a piece perfectly clear can be obtained for telescope lenses. These are made almost entirely in France. The typical method of preparation is to carefully select a lump of high specific gravity, and placing it in a clay disk mould, slowly flatten it down by heat into the desired shape. Sometimes the glass is delivered to the lens. maker in rectangles, which are cut. into disks by an annular saw.
The famous Alvan Clark establishment in Cambridge, which has furnished the Pulkowa. Washington. Lick, and other great telescopes with objectives, polishes with infinite pains the slabs received from France. In this modest workshop the most efficient instruments of astronomy have been equipped. How delicate its results are may be judged from the fact that a finger touch upon a lens swells it sufficiently to create a prominent spot in the tests applied. The 36inch objective of the Lick telescope, the largest yet made, would seem to be a sufficient triumph, but the Clark brothers are confident of their ability to make one 40 inches in diameter. The cutting is done by castiron sand, which, by a rapidly rotating machine, gives the general curvature. Then the patient polishing is done on an iron lap coated with pitch and fed by water and rouge. There are eight manufactories of fine lenses in this country, but roue west of Rochester, which is the main centre for microscope, camera, and eye.glass lenses. The glass is now furnished to our manufacturers in plates six to nine inches square and an inch thick. Being made only abroad, it enters without duty, but is worth $10 a pound in the rough. An annular saw cuts it into disks. These are sawn by the help of emery into thin pieces, which, cemented to sticks, are ground into concave or convex circles, and then ground oval for their frames.
* One of the most wonderful specimens of glass in the world is to he seen in the Conservatoire of the Arts and Trades at Paris. It is the life-size figure of a lion in the act of stifling a serpent. Every part is marvellosly natural, and it is male entirely of glass. It cost the artist, M. Lambourg, thirty years of work, and was conspicuous in the Universal Exposition of 1855. At the Paris Exposition in 1878 there was exhibited a bonnet with feather, ribbons, and lining made entirely of spun glass, as well as cloaks and other articles of wear.Besides the enormous range of uses in which glass familiarly achieves a unique purpose, it does many strange services, and every year adds to the catalogue of its unsuspected virtues. From the material that produces Prince Rupert's drops, combining in one bead the toughness of iron with the explosiveness of powder, we may expect anything. A favorite amusement of glass-workers is to reel out fine threads quickly drawn from a molten batch, making a mineral silk to spin into incombustible cloth or to fashion into the plumage or hair of animals. Especially in Austrian factories the glass is woven into fabrics, sometimes with a warp of silk, or made into collars, neckties, chains, brushes, lamp–wicks, etc.* Recently a mineral cotton has been made from the slag refuse of iron smelting. The crude glass is melted and brought before a fierce blast, which blows it into delicate shreds, white and soft, that make a fire and rat proof filling for walls and floors. Exposure to great heat and gradual cooling devitrifies glass, transforming it to "Wanmur's porcelain," opaque and crockery-like. "Soluble glass" is a highly alkaline solution of quartz, potash, and charcoal, which is applied to textures in theatres to preserve them from flames. If fire touches them it melts the invisible minerals into a glaze, which excludes the air and prevents combustion.
The future of the glass industry in the United States is encouraging, for it is only since the war that the manufacture of polished plate has grown up; and there are now running, or building, enough furnaces to supply all that will be used in the country. It is within the last ten years that the manufacture of cathedral and rough plate has been thoroughly established, at first disputing and now controlling the home market against England and Belgium. The improvement in window-glass has also been great, and there are workmen and manufacturers who think they see the rising sun of much better days and a much better American glass. The concentration of capital in powerful concerns must certainly lead to changes in the system of labor that are bound to insure a more finished product. A new glass recently invented in Germany is said to add marvellously to the power of the microscope. A Yale professor announces the invention of a perfect acromatic telescope lens.
Legend tells of the lost invention of "malleable glass." Tiberius is said to have discouraged a genius who found the secret by beheading him, fearing the innovation would reduce the value of gold. It is also recorded that Cardinal Richelieu was presented with a bust of malleable glass by a chemist, who purposely let it fall into fragments, and mended it before his eyes with a hammer. The inventor was promptly rewarded by perpetual imprisonment, lest his ingenuity should ruin the "vested interests" of French manufacturers. But if glass may not ape the metals in malleability, it may imitate them in another respect just as important. A more fortunate Frenchman (M. de la Bastie) has within a few years introduced into Europe a transmuted glass which, he claims, may displace castiron. If it fulfils his expectations it will mark a new era in glass, and the old adage "as brittle as glass" will be superseded by a new one, "as tough as glass." By his process railway sleepers, fence posts, drain pipes, tanks, etc., are cast in moulds, and so toughened by a bath in oils as to be stronger than iron, though much lighter, and costing onethird as much. But it is questioned whether his results reach what is claimed for the process.
These undeveloped toughening processes augur astounding changes in the future of glass. "Glass houses" may become the fashion, and we would have to reverse our proverb about them, for they would be bombproof. Already transparent glass bricks are made. Extending the possibilities of glass a little further, why may we not build the entire structure of glass? The walls might be cemented blocks cast like hewn stone, but translucent, and of any color. One could thus inhabit a huge pile of amber or of gigantic gems. The windows could be multiform, some of them telescopic, bringing distant things near, some with lenses or mirrors guiding the focussed sun's heat for culinary and comfortable purposes, others straining out the light or chemic rays. Tapestries, furniture, and utensils might be made of the universal material. The whole would be more endurable than granite. No fire could harm it; lightning would shun it. Such a dream, blossoming from this miraculous substance, may be realized by an Aladdin whose lamp is of glass.
Authorities.
The government Report on the Manufacture of glass, by Joseph D. Weeks, 1880, is the best summary of the industrial history and condition of glass at the last census.
La verre, son histoire, sa fabrication, E. Peligot, Paris, 1878, is the most comprehensive work;
Guide de Verrier, G. Bontemps, Paris, 1868, is the technical guide to the manufacturer;
Curiosities of Glass-making, H. Pellatt, London, 1849, Marvels of Glass–making, A. Sanzay, London, 1869 (from the French), and Treatise on the Origin, Improvement, and Present State of the Manufacture of Porcelain and Glass, London, 1852, are the best English textbooks.
Glass by Alexander Nesbitt, London, 1878, the handbook of the South Kensington series, is the authority on glass history; Mr. Nesbitt is also the author of the historical chapter on Glass in the Encyclopædia Britannica.
See also the encyclopædia; "Glass–making," by Professor C. H. Henderson, in the Journal of the Franklin Institute, September, 1887; and Harper's Magazine, Vol. XLVIII., p. 320 ("Some Notes about Pottery and Porcelain," by William C. Prime); Vol. L., p. 386 (" Glass-making," by E. H. Knight); Vol. LIX., p. 655 ("Painted Glass in Household Decoration," by Charles A. Cole).
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