An Ancient Liquid Serves a Modern World
By “Awake!” correspondent in Canada
A LIQUID for packaging and architecture, engineering and art! Essential to automobiles, radio, television and satellites, it is indispensable in hospitals, factories and homes. It can be as strong as steel, hard as gems, heavy as iron; or fragile as eggshells, soft as silk, light as cork. Supplied in abundance surpassed by few other materials, it is the liquid of antiquity—glass.
“Glass—a liquid?” you may ask in disbelief. Yes, when glass is formed from a white-hot mixture of molten ingredients its atoms and molecules retain the random pattern of a liquid even though it becomes as rigid as ordinary solids. A liquid that looks, feels and behaves like a solid seems fantastic, but the peculiar properties of its unique state make glass one of your most versatile and valuable servants.
Glassmaking is one of the most ancient industries. It is also very modern. Man has used glass for more than thirty-five centuries, but he barely “scratched the surface” of its versatility until about seventy-five years ago. In fact, it was not until 1903 that a glass bottle was produced entirely by automation, and a machine for flat-drawing window glass was not a commercial reality until about 1916. Since then increased knowledge and better means to utilize this amazing liquid have allowed mass production to transform glass from a treasured luxury to a servant in myriads of forms.
The basic ingredients of glass have remained unchanged for thousands of years. Silica sand, lime and soda still make about 90 percent of the world’s glass, but the production scale has been considerably increased to meet modern demands. Today’s glassmakers scrupulously select tons of pure raw materials, weigh them to the ounce, thoroughly mix them and then feed the mixture, or batch, to gigantic tank furnaces that can hold more than 1,000 tons of molten glass. Although added cullet, or scrap glass of the same formula to be manufactured, speeds the melting process, the furnace must be heated to about 2,800 degrees Fahrenheit! So corrosive is molten glass at this temperature that the process has been compared to melting a block of ice in a container of sugar. The heat-resistant furnace walls must usually be replaced every two to four years.
However, once the process is in operation it continues day and night, week after week, until repairs or changes in formula force a shutdown. The batch is continuously fed into one end of the furnace while workable glass, mixed and refined to uniform viscosity, free of bubbles and impurities, is drawn from the other. The red-hot liquid is then ready to be drawn, pressed or blown into your service.
Although some fashionable Roman homes during the first century C.E. boasted almost transparent glass windows, little more than a century ago they were still considered a luxury. Today the annual production of window glass would stretch for thousands of miles as the ancient liquid is drawn, cut and framed to provide light, reduce noise, keep heat in and cold out.
Ordinary window glass is drawn from the drawing kiln, a small extension of the furnace. To begin production an iron grill bait is lowered into the melt and slowly raised. The molten glass is fluid enough to flow, yet viscous enough to adhere to the bait so that it rises vertically in a continuous sheet! The bait is knocked off as electrically driven rollers carry the hardened liquid some thirty feet straight up to a cutting loft where the fire-polished sheet is cut into standard lengths.
The surfaces of sheet glass produced by this method are not perfectly parallel, causing slight visual distortion through the glass. For optically superior windows and mirrors, flat glass, drawn from the furnace, moves horizontally as a continuous ribbon a thousand feet long through gigantic grinders. It is ground on both sides simultaneously to near perfect flatness. The plate glass is then cut into sections and polished to provide an undistorted view of the road for some motorist, or to fascinate a little child with his flawless rosy-checked image in the glass.
A revolutionary new process for the manufacture of quality plate glass was announced in 1959. Called the float process, it eliminates entirely the costly grinding and polishing procedures.
Molten glass flows from the furnace in a continuous strip directly onto the surface of an enclosed pool of molten tin. The glass is kept hot enough for all irregularities to melt out while the surfaces become perfectly flat and parallel. The glass is carefully cooled as it progresses along the float bath to emerge distortion free with hard fire-polished surfaces.
Float glass has been met with enthusiasm, especially by the automobile industry, which gobbles up about 50 percent of all the flat glass manufactured annually.
A Variety of Uses
Each year glass provides 29,000,000,000 containers for everything from baby foods to corrosive acids. No other material known can match this service made possible by the ancient discovery that hot glass can be blown into almost any form. Modern technology applies this discovery for mass production at fantastic speeds.
When bottles or jars are being made, gobs of glass fall from the furnace into “blank molds” so fast that they are almost invisible! A plunger forces the glass into the shape of the initial mold and the glass is then transferred to a “finishing mold” where compressed air blows it into the final shape. Metal jaws swing open, and out comes the container, still glowing red, about six seconds since the glass left the furnace!
An Ancient Art
Impressive as these complex machines may be, it is the glassblower who truly enthralls the watcher. Using a few simple tools and traditional skills of an ancient craft, this artisan persuades the liquid into articles of intricacy and beauty beyond the reach of automation.
Artistic glass and fine tableware are the products of “offhand blowing.” The techniques of this classic profession date back hundreds of years. When Venice was the capital of the glass industry in the fourteenth century, her glassblowers could be punished with death if they revealed the secrets of this art. Later, about the middle of the seventeenth century, a lustrous, transparent glass particularly suited to offhand blowing was developed in England. Known as flint or lead crystal, it is the type most in demand for modern treasures in glass.
The glassblowers function as a “shop” of six or seven men. First the “gatherer” takes the required amount of molten glass on the end of his blowing iron. About five feet long, this hollow iron pipe has a mouthpiece at one end and a knob at the other. To the inexperienced the blowpipe is a long, clumsy tube, but to the master glassblower it is the inseparable partner of an artist and his craft.
The gatherer shapes the hot glass by rolling it on a “marver” or machined iron plate. A puff through the pipe forces the glass into a preliminary form. Various workers add their skills to shape the glass, rotating the blowpipe constantly to keep the soft form from sagging out of shape. Swinging the blowpipe elongates the glass; rapid spinning flattens it out. Shaping tools spread an open end or pinch in a narrow neck, flatten edges, round the gob and trim off excess glass. Size, shape and thickness depend upon the air blown into the glass, the angle at which the blowpipe is held and the rate at which the glass is allowed to cool. From time to time the glass must be returned to the “glory hole,” a reheating furnace, to keep it hot enough to be workable, about 1,800 degrees Fahrenheit!
Throughout the operation the watchful eye of the “gaffer” guides the art piece to its final beauty. As the shop’s master blower he handles the more difficult jobs himself, relying upon many years of acquired skill to utilize the fluid, graceful motion of the glass to achieve clean, flowing lines. His knowledge of where and how the glass will fall is almost unbelievable. When the gaffer’s artistry is fulfilled and he is satisfied the piece is flawless, it is placed in the annealing oven to be gradually cooled.
During the final forming the glass is attached to a long, solid “pontil” rod that leaves a mark in the base. This mark is ground smooth, leaving on some pieces a shallow depression, which is an indication of genuine handmade glass.
The object may be decorated by cutting or by the difficult art of copper wheel engraving. The engraver may use as many as fifty rotating wheels of different diameters, fed with emery powder and oil, to cut a shallow design that appears to the eye as low relief. The brilliant quality of the glass captures light and plays it through the engraver’s masterpiece. Such items of the ancient liquid in aesthetic form can be worth thousands of dollars, reminding us that glass may still be counted in value with precious gems, just as it was 3,500 years ago.—Job 28:15-19.
The degree to which properties of glass can be varied and controlled is so great that over 100,000 formulas have been developed for different uses. Variations of lead crystal provide insulators for electrical circuits, neon lights and precision optical lenses. Pure silica glass makes mirrors for satellite telescopes and laser-beam reflectors. Special glass to withstand heat of reentry and cold of outer space serves space vehicles with windows.
Combinations of special formula and special treatment give colored glass panels, building blocks and insulation to decorate and protect modern buildings. Tempered and chemically toughened glasses add to your safety. Colored glass protects your eyes. And now the new families of fiber glass and glass ceramics appear almost as richly versatile as their ancient parent!
Indeed, this amazing liquid of antiquity is your modern servant in a thousand forms, asking in return only an occasional cleaning that its brilliance might continue shining brightly.