What’s New in Glass ALEXANDER SILVERMAN University of Pittsburgh 13, Pittsburgh, Pa.
Much is new in the age of glass. In refractories, plate glass, window glass, hollow tile, table ware, bulbs, tubing, fiber glass, foam glass, optical glass, and photosensitive glass, new developments are continually being made for use in industry, the home, and the laboratory.
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HAT’S new in glass may, on occasion, be old in years, but archaeologically new. Recently J. C. Harrington of the National Park Service, in an investigation partly subsidized by the Glass Crafts of America, an association of manufacturers of hmd-made glass, excavated proofs of the existence of a glass factory on the mainland of Virginia a t Glass House Point, opposite Jamestown Island. This factory, located about a mile from Jamestown in the colony of Virginia, was established in 1607 according to Captain John Smith, who stated in his ‘(History of Virginia” that it was the first industrial enterprise in the American colonies. Accordingt o Harrington, it was built in 1608, and the buildings covering about 37 X 50 feet housed a melting Eurnace, a kiln for firing new pots, a fritting oven, and an annealing furnace; there were also a clay pit and a oullet pile. The furnace was built of clay and large cobblestones. The reconstruction program should be complete by 1956, when visitors to Glass House Point will be able to see glass made as it was in 1608. The old factory supposedly made bottles and beads for trade with the Indians. KO beads have been found. MELTING EQUIPMENT AND CONTROLS
High-temperature refractories, zirconia, and electric-furnace high alumina are now available. Pots are cast fmm slip instead of being built by hand. In the newest tank furnaces glass is melted by gas with supplementary electric heat, or entirely by electricity. Tanks may be heated by the electrical resistance of the molten glass, or by electrical resistors. Graphite electrodes, both horizontal and vertical, are employed. Thermostatic control is possible for both gas and electric melting, and controls are now located not only in melting and refining sections of tanks but at other points. Pressure controls regulate gas and air; automatic chemical controls regulate their proportions. PLATE GLASS
While the invention in 1688 by Lucas de Kehou of France still applies where plate glass is cast from pots, many improvements have been made. The continuous rolling of plate now predominates. Huge tanks melt and feed the glass to stainless steel or None1 rolls, whence it travels to the grinding and polishing tables. Most factories still grind and polish one side and then turn cut sections, to grind and polish the other side. Plate glass is now ground continuously and simultaneously on both sides in England, France, and America, but is not yet polished continuously on both sides. Researches are under way to make continuous polishing possible. Plates have been drawn 500 feet long and marketed in 50-foot lengths. For special uses, precision grinding and polishing have yielded almost unbelievable uniformity of surface level. A study of January 1954
polishing materials has indicated the significance of their crystar forms. Substances crystallizing in certain systems serve best. Colored plate is being produced in a considerable variety of new shades, and finding use in the internal and external facing of buildings. The “picture window” has brought plate glass into the home, where i t may also serve in sliding partitions. Glass tops are used to protect fine wood finishes; entire glass tops of heavier plate are a part of special furniture. Plate glass is metallized with a continuous ribbon pattern of aluminum for electric resistance-radiators for the bathroom and for general use in the home; horizontal plates are attractively mounted for buffet use in the dining room. Plates of various thicknesses are laminated by new transparent plastic binders to ensure safety in automobiles, busses, trains, airplanes, and bank windows. Panes for vehicular use have the plastic binder extended for mounting in metal frames; shock is abeorbed and breakage is minimized. The new plastics do not cloud or discolor. Plate glass surfaces can be coated with transparent layers of tin salts and other compounds, which are fired on. Their electrical resistance heats the pane. Used on the laminated side, they prevent ice formation on windshields. Other externally applied coats radiate heat. They may be used in space heaters and wall radiators. As ceiling radiators in poultry pens they prevent huddling of chicks in the cold, thus guarding against the spread of disease, and encouraging more rapid growth of the chicks. Conducting laminates coated with phosphors radiate soft light, but do not heat appreciably. They may be used for wall and ceiling illumination. I n time they may replace bulbs and tubes in the lighting field. The newer tempered or case-hardened plate, produced by methodicallyheatingand chilling surfaces uniformly,is much stronger than ordinary plate, It is used for glass doors and other special applications. Localized tempering provides transparent sections in panes, to prevent accidents in motoring and aviation. Greenish-blue plate glass containing ferrous ions absorbs heat. Once discarded in favor of colorless plate which did not absorb heat, it has again come into vogue in the motor car, factory, office building, and home, where i t ensures lower temperatures in hot weather. A new colorless phosphate glass, containing ferrous ion, also absorbs heat. Silvered plate glass mirrors are not new, but improved wet silvering formulas and cold spraying techniques have resulted in greatly improved deposits which are equally bright on both sides, and practically free from pinholes. They may be opaque or transparent. They can be laminated. Mirrors are also produced by condensing vapors from electrically heated metals on cool glass surfaces in vacuo. Aluminum mirrors are opaque. They re-
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Fiber Glass Sleeve-Covered I n g o t Ready to E n t e r Die
flect the visible spectrum and ultraviolet better than silver; besides, they are on the near side of the glass and prevent color contamination produced by the glass in silver mirrors where the mirror is on the far side. Chromium mirrors have a brownish tint; they may be made opaque and in all degrees of transparency. They are very durable. WINDOW GLASS
Window glass is drawn vertically continuously through a slotted clay float, or debiteuse, from glass in a special forehearth of a continuous tank. Convection currents make the process selfannealing in the Fourcault process. Glass is also drawn vertically by the Colburn process, in which the rising sheet is heated after stable form is attained, and passed horizontally over a large rotating cylindrical roll to the annealing ovens or lehrs. The Fourcault process is now operated entirely by electricity for both melting and debiteuse control in a number of factories. Drawn sheet glass, through composition improvement and the constancy resulting from technical control, may now approximate plate glass in perfection. It has the advantage that surface layers have not been removed by grinding and polishing. In Europe the Fourcault process has been used with various degrees of Nuccess for drawing cased glass containing a heavy crystal layer, and a thinner opal or colored layer, which is drawn from a smaller contiguous tank. DOUBLE GLAZING
Assuming that other insulation in a building is good, double gla~ingwill result in further fuel economy. When the outside temperature ia 15" F. and the inside temperature of a single window pane is 30" F., that of a double pane will be about 50". Humidity is an important comfort factor. Again assuming good insulation in other parts of a building, the per cent relative humidity indoors a t an outdoor temperature of 15" F. would be about 20% for single glazing and 50% for double glazing. Recently it has been found possible to weld the edges of double panes. What has been said of surface treatment, lamination, etc., for plate glass also holds for high-quality window glass. HOLLOW TILE
Hollow t i e is widely used in construction today. The halves of the tiles are pressed from molten glass and welded or cemented together. While used commonly in cement or concrete build144
ings, hollow tile is capable of artistic architectural application. Though a natural insulator through its air cell, i t may further insulate against heat through ferrous ion content, and may direct light through special prismatic design. TABLEWARE
In modern tableware we find blown warelike tumblers, and a great variety of pressed ware, or blown and pressed combinations. Drinking glasses have not been and never will be supplanted by plastics. They have a "feel" in contact with the lips which is characteristic and to the human liking. Pressed plates, cups, saucers, and other dishes in attractive designs and colors are in increasing demand. Expanded pressing from a soft mass dropped into a concave mold results in uniform speading of round plates and saucers with rounded edges. CONTAINERS AND BULBS
Automatic bottle machines of several types are in use. In one glass is sucked into a mold; in another gobs or uniform-size chunks of soft glass are dropped into the mold for pressing and blowing. The latter type and the double-gob method predominate. Jars of various designs are produced automatically on press machines by the gob method. Both rotating and lateral swing machines are in use. During 1952 over 15billion containers were made. The composition of bottle glass has been changed to improve durability and strength and permit thinner and lighter ware. The one-way bottle has resulted, Special bottle compositions are available for special purposes. Tube vials and ampoules are made from tubing by machines which automatically burn them off and produce finished vials and ampoules ready for sealing. Here again, special cornpositions are used. I n the Westlake bulb machine the jackets for lamp bulbs are still blown to a high degree of perfection. Recently a machine has been developed which blows bulbs from a ribbon. The ribbon with lenslike protrusions is formed from glass which flows continuously between rolls having lenslike depressions. The ribbon then travels on an automatic conveyor onto which blow heads are lowered over the lenses, which are blown into bulbs through openings in the conveyor. The bulbs enter rotating paste molds. When fully blown, they are severed from the ribbon mechanically and dropped onto another conveyor which carries them to the annealing oven. I n one eastern factory, the
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continuous-ribbon machines produce over a million bulb jackets per day. In the museum a t Nela Park are found, in addition to assemblyline items, electric bulbs ranging in size from a grain of wheat to a 12-inch high-power tungsten lamp. Glass encloses the argon and neon bulbs of the landing field, the sodium vapor and arc lamps of our streets and highways, the floodlights of the studio, even the 2,000,000-candle power beam of the searchlight. It makes possible the infrared heat lamp, the sun lamp, and the x-ray bulb. It gives us radio and television and the motion picture, whose very screen is rendered more brilliant by embedded glass beads. X e w television glasses are darker and prevent glare and eyestrain. .4nd what of radar? TUBING
For smaller sizes tubing is drawn horizontally in the Danner process, where glass flows from the melting tank onto an inclined hollow rotating mandril. This is fed with compressed air a t one end, which forms a glass bubble a t the other end. The bubble is attached to a mechanical lead which draws it continuously into tubing whose diameter and wall thickness depend on rate of glass flow onto the mandril and rate of elongation of the bubble. Larger tubing, 2 to 6 inches in diameter, may be formed bv vertical gravity elongation of an extruded glass bubble, or by upward drawing of glass from a melting tank on a cylindrical bait as in the old Lubbers process for making window glass. In the latter, wall thickness depends on rate of draw. Sufficient air pressure is maintained to prevent collapse of the soft glass. Tubing is employed not only in the laboratory, but for the manufacture of hypodermic needles, ampoules, tube vials, parts of lamp bulbs, and fluorescent lamps. Uniform internal diameter is now possible. Recently tubing has been used to create art effects, as in the Corning Museum and the Johnson-Wax Research Building. Here it not only lets light through, but may serve for heat regulation. Large tubing may be welded by gas or electricity, and it may be fianged and fitted with metal couplings. In a number of beverage plants, many miles of transparent glass tubing continuouslj7 convey the liquid products during processing or treatment. GLASS
woaL AND
FIBER GLASS
Just as tubing is an elongated glass bulb, so solid glass when drawn out forms rods and fibers. Probably on branch of glass making has enjoyed the rapid expansion and prosperity that have come to fiber glass. Blasted from molten glass by air or steam, it forms wool and bats, or staples which are used as insulation. The heat-insulating power of a bat 4 inches thiek is said to equal that of a 10-foot concrete wall. Fiber glass is rodent- and vermin-proof. Acidleached, high-silica fibers have higher melting points and are used for high-temperature insulation. In this field new cornpositions are also possible. Special fibers absorb and/or transmit specified radiations. Their composition may not be disclosed. They must meet rigorous specifications. Treated bat is used as a filter in air conditioning. Supported by a plastic it also replaces feathers, ramie, and kapok in pillows and in upholstering. Molten glass may be drawn or elongated into long filaments or fibers, which may vary from a fraction of an inch to many feet in length. They may be gathered as floss or yarn or assembled and twisted into threads. These may be woven into fabrics, from the sheer marquisette of curtains to heavier cloths used in upholstering, draperies, and even filter cloth. With increased drawing perfection fibers diameters have decreased in diameter so that skin irritation can be avoided entirely, and fabrics are as soft as silk. Diameters of a micron or less are within control. By surface treatment the fibers can absorb dyes, and cloth is now obtainable in many colors, attractively woven, or printed with patterns. The fabrics are nonflammable. January 1954
COURTESY CERAMIC INDU8TRY
Glass Bubbles for Aerating Hydraulic Cement Compared in Size with Small Thumbtack
Glass floss and sutures are used in surgery. Glass woven with low-melting plastics is replacing plaster casts for supporting broken limbs. The wearer can bathe and go about freely. Being porous, it prevents skin irritstion. With a tensile strength of close to a million pounds per square inch, fiber glass is probably the most important plastic-reinforcing material of the day. Already used in furniture and in water-, motor-, and aircraft, it promises to become an important structural material. To the author’s knowledge no other material possesses tensile strength in fiber form equal to that of glass. One of the newest applications of fiber glass is as a lubricant. A glass-cloth sleeve is placed over a red-hot steel ingot before i c t is forced through a die. The glass melts, serves as a lubricant, and lengthens the life of the die which would normally be eroded very rapidly. Colored fibers have been used in art windows in Italy. The fibers are affixed to a transparent pane of glass with water-glass, the design is allowed to set, and is thencovered withasecond transparent pane. The colored fibers also find use in American art glass. FOAM GLASS
This product of glass powder, mixed with a gas-producing agent like bitumen, soft coal, or soda ash, and heated until the molten glass forms a foam, may be made in molds or rolled continuously. The color is black or white, depending on the gasproducing agent. It may be molded to shape while hot or cut with a saw when cold. Like fiber glass, it is rodent- and verminproof and a fine heat insulator. It does not sag or settle like glass wool. It is so light that it floats on water and as a raft will support several men. It can be enameled in colors. Recently white foam glass was sculptured for attractive murals on the Steamship United States. BEADS AND BUBBLES
Beads are produced by dropping small fragments of glass through heated zones. They fall under the force of gravity and are melted and rounded. They are used for making motion picture screens and road markers. Bubbles are produced similarly by dropping fragments of clay. The water in the clay renders the particles porous. They
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Continuous IJouble Grinding of Plate Glass
are used in hydraulic cement to render it more porous and thus improve heat insulation. OPTICAL G L 4 S S
Optical glass is sometimes melted in open pots which are allowed to cool slowly, and optically clear chunks are selected and worked. Now the glass is frequently poured onto steel tables, rolled like plate glass, then annealed, cut into blanks, ground, and polished. Sometimes the blanks are remelted and reshaped into lens blanks of special design. Weight is controlled. Lens blanks and lenses may be pressed directly from molten glass or from softened ribbons or rods of glass. For grinding and polishing, blanks are attached to a warm plastic mass which sets on cooling. To make it unnecessary to pry the finished lenses loose and possibly injure them, the lenses on their supports are sent through a freezing tunnel, which shrinks the plastic and cracks &hemloose. Lenses may be cast. This is particularly true of large blanks like the one employed for the 200-inch American reflector on Mount Palomar and the 120-inch reflector a t Lick Observatory. The 200-inch reflector has enabled astronomers to view the heavens many galaxies beyond former limits. Optical glass includes colored glasses. In this category belong the newer television glasses which have been devised to reduce light intensity of the tubes and prevent strained vision. Then fhere are welder’s goggles for use in electric and oxyacetylene welding, and the almost infinitely varied sunglasses. Glasses of the television and goggle type are now drawn continuously by the Fourcault process. Elaborate studies are conducted to debrmine compositions that will absorb undesirable rays. Glass compositions are known which merely dim the light without appreciably altering the color. Some of these lenses enhance reds and greens. Special glasses are available that will absorb or transmit almost any desired wave length. They can absorb or transmit infrared and/or ultraviolet and transmit or absorb x-rays. Sow they ran absorb high-energy x- or gammarays and slow neutrons so that transparent barriers may be available for atomic energy Lyorkers, instead of bulky concrete walls with periscopes and mirrors for indirect observation. These
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glasses are also possible for colorless and colored spectacle lenses and parts of optical apparatus. The new x-ray absorbers are more efficient than older ones, and discolor less readily. And for special wave absorption, there are red flasks for use in vitamin C determinations, and ultraviolet-transmitting flasks to stop growth of cultures in their containers a t any desired moment. Instead of shaping plate or sheet glass blanks, balls are blown with the desired lens curvature. Lenses cut from these have the natural surface films of the blown glass, which have not been lost as in ground and polished lenses. Refraction and dispersion have received serious study. The index of refrartion of optical glasses is rapidly approaching 2 and products of very low dispersion are available. Some of these glasses are especially valuable in wide-angle photography; some are in use in new cataract lenses which are thinner and therefore lighter than the old heavy lenses. Before Ernst Abbe and Otto Schott came to Jena, Germany, abo& 1880, only five or six chemical elements and their compounds were used in glassmaking. The two scientists, through thcir researches, added about 25 elements in the next quarter century. Today, practically all normally solid elements and their inorganic compounds have found a place in glassmaking and research. Organosilicon compounds are bridging the gap between organic and inorganic chemistry. Tetrahedrally surrounded by oxygen like the silicon of glasses, their silicon has an interesting affinity for glass, enabling the silicones to adhere t o it. The coats are water-repellent. They make it unnecessary to place paper sheets between panes during storage and shipment, and they protect the surface against scratching. GLARE PREVEVTION
Not too many years ago magnesium fluoride was vaporized onto glass surfaces to lessen reflection, as it was found that an untreated lens surface reflected about 10% of the incident light. Applying this principle to a multiple lens system with numerous faces meant a serious light loss and the slowing down of lens speeds. The use of various surface agents has increased lens speed and efficiency greatly. The principle has also been applied to sheet glass for covering paintings, and used to increase visibility generally.
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-Ceramics SPECIAL COMPOSITIONS
Glass to approximately the properties of transparent fused silica has been produced. Borosilicate glass, fairly rich in alkalimetal compounds, is leached with aaid, which removes almost every component except’ the remaining hydrated silica. On reheating, the opalescent mass re-fuses, retaining its original shape and becoming clear, but having shrunk about 15%. Fused alumina and very-high-alumina glasses are used as jewel bearings. Aluminum phosphate glass resists attack by hydrofluoric acid. Photosensitive glass is a fascinating new development. Gold ruby glass has been known for many years, and it was known that colorless gold, silver, copper, and selenium glasses would develop color on reheating. More recently it has been found that the colorlessglassescanbecovered~vith a mask or negative andprinted by exposure for 10 minutes or more under arc light, with subsequent development by heating below the softening point of the glass €or an hour or more. The photographic effects within the gl:ass, which depend on the size of colloidal particles, are astounding, and a variety of colors results, depending on the intensity of reflected or transmitted light in which the photograph or pattern is viewed. More recently still, a clear colorless glass has been produced which becomes milk-white when treated as indicated above. The parts are selectively soluble in chemicals, and with proper exposure, patterns may be eaten entirely through the glass in places. The pattern partly etched may serve for embossing or engraving plates. The possibilities are far beyond conjecture for both art and technology. CONSTITUTION
X-ray studies and the use of absorption spectra have disclosed much regarding the structure and composition of glass. Glass-
forming and glass-modifying elements have been classified. .4 knomledge of atomic and ionic radii, of chemical bonds, and of magnetic and electronic relationships enables the mathematical physicist so to predict, that considerable experimental work is eliminated. The chemist, the physicist, and the engineer have brought us into a new glass era, one that might well be christened “The Glass Age” after the material which is so indispensable to modern man. ART
I n the Catholic Shrine in the nation’s c,ipital reposes a beautiful glass mosaic replica of Murillo’s “Immaculate Conception” from the Vatican in Rome. The Vatican studios have over 50,000 color tones available Though not comparable in art or beauty, other glass mosaics find wide application in architecture Examples are found in the murals of the City Hall in Stockholm, Sweden, in the Union Station in Cincinnati, and in the murals and columns of the new structure which serves as AMERICAN C~IEVICAL SOCIETY headquarters a t this moment in Los Angeles. America and Europe both produce fine crystal, some of which is engraved, cut, and decorated by the foremost artists of our times. Use of the diamond point for stippling and line drawing has been revived in Sweden. The introduction of color in art ware is gaining popularity Attractive art glass is on display periodically at glass shows in our larger cities. Stained glass of .4merican manufacture is found in beautiful windows designed by American artists and installed by rlnierit an artisan7 in our churches. Much is new in the age of glass. RECEIVED for review Spril 11, 1953.
ACCEPTED October 30, 1953.
Microscope ALBERT F. PREBUS, The Ohio State University, Columbus, Ohio JOHN W. MICHENER, Owens-Corning Fiberglas Corp., 1V~i4~ark. Ohio U
Evidence of structural inhomogeneities in glass up to several hundred Angstroms in maximum dimension has been obtained, using the electron microscope. Direct transmittance electron micrographs show the structure with a high degree of contrast. There is a wide variation in structure among the various glasses investigated. The structural evidence is interpreted as indicating the possibility of a relatively high degree of order over distances ranging from 20 A. up to at least 200 A.
A
CHASCE observation of a tapered fiber of borosilicate glass revealed a granular or spotty appearance in that part of the fiber which was small cnough to allow transmission of the electron beam, thus iendering a transmission photograph of the fiber-as opposed to a shadowgraph-which is obtained for larger fiber diameters. This first fiber was one of a much larger group which was being shadowgraphed as a means of determining fiber diameter. This particular fiber tapered from a diameter of well over 1000 A4.to less than 100 -1.and was increasingly transparent with decreasing diameters brloiv 1000 A. This first direct indication of observable structure led to the beginning of a program directed toward an understanding of this structure. The progress January 1954
of this program to the present time is reported here. Severd glasses in different forms which have different thermal histories have been investigated. Previous investigators studying various physical properties of glass have arrived a t widely varying ideas of the structure of glass. Many have estimated inhomogeneities in structure ranging from nearest neighbor separations up to several hundred Angstrom units. Warren’s (a)x-ray diffraction work appeared to give the most direct indication of this inhomogeneity of glass structure and indicated that there x-as no crystalline order in one dimension beyond a distance of approximately 7 A. This conclusion has been broadly interpreted by others as indicating
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