by Eric Flint
In 1903, John H. Lubbers partially automated the medieval Lorrainer method. A circular bait, at the end of a blowpipe, was dipped into a draw pot, and a cylinder of glass was drawn up. The cylinder still had to be manually cut and flattened. Nonetheless, the Lubbers technique allowed the fabrication of larger sheets of glass by less skilled workers. This method is mentioned in the 1911 EB, although that reference mysteriously remarks that during the drawing operation, the cylinder is "kept in shape by means of special devices."
By 1905, Emile Fourcault succeeded in vertically drawing a continuous sheet of glass directly from the glass furnace. The Fourcault process is also described in the 1911 EB. However, it naturally does not reveal the improved process (featuring a device called a debiteuse) which Fourcault developed in 1913, so the glass did not narrow at the base as the leading edge was drawn up (Douglas, 155). The drawn glass was still marred by rollers, and needed to be ground and polished to be suitable for optical use.
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What truly revolutionized the plate glass industry was Alastair Pilkington's float glass process (1952), in which the glass spreads out over a layer of molten tin. Because the surface of the molten tin is flat, the glass also becomes flat, settling to a thickness of six millimeters.
The Encyclopedia Britannica favors us with a schematic diagram of the Pilkington float process, and with a few process parameters. It is certainly worth trying to duplicate once we have mastered the earlier plate glass production methods. However, it is important to recognize that it took seven years, and seven million pounds, to reduce the idea to practice, using 1950s' technology. We do have the advantage of having a description of the perfected process, but there is no doubt in my mind that the explanation leaves out important details. For example, the operator needs to control the viscosity gradient by appropriate settings of the water coolers along the process line. And some of the details it does give, such as the need for a controlled hydrogen-nitrogen atmosphere to prevent oxidation of the tin, are daunting.
New Manufacturing Methods: Mirror
The down-time state of the mirror-making art was the technique developed by Venetians Andrea and Domenico de'Anzolo del Gallo in 1507. They realized that the Venetian cristallo could be given a highly reflective surface by hammering tin into thin sheets, amalgamating it with mercury, and then laying the sheets of cristallo onto the amalgam.
We can greatly improve upon this century-old technique, dispensing with the poisonous mercury, and also obtaining a more uniform coating of controllable thickness. In 1835, Justus von Liebig discovered that silver could be deposited in a thin film on glass. There are many variations on the Liebig process, but in all of them, a solution of a silver salt is used as a source of silver ions. A reducing agent reduces the silver ions to neutral silver atoms, and the latter are deposited on the glass. In Liebig's original work, an ammoniacal solution of silver nitrate was heated with and reduced by an aldehyde (e.g., formaldehyde) to elemental silver. The process was commercialized in the 1840s, and true silvering replaced foiling.
Two related methods of reduction by solution have been developed. In the "hot" silvering method, the ammoniacal silver nitrate solution was boiled, and the condensing steam was reduced with tartaric acid (more precisely, with Rochelle salt, the sodium-potassium salt of tartaric acid.) This deposit method is slow; it may take an hour to form a thick film. For this reason, the "hot" or "Rochelle Salt" process is favored for making "one-way" mirrors, which have a partially reflective surface (Newman, 317, 322). In the "cold" method, the reducing agent is sugar (Gregory, 158). This is also called the Brashear process.
An improvement on the basic method is to sensitize the glass so it more readily accepts the metal. This is usually done by "tinning"; treating the glass with a dilute stannous chloride solution (Newman, 15, 314).
Originally, silvering solutions were poured onto the glass. However, they can be sprayed on, instead. Typically, two jets are used, one supplying the ammoniacal silver nitrate and the other a fast-acting reducing agent such as hydroxylamine sulfate (Schiffer, p. 7).
There are alternatives to silvering, such as aluminizing, but I don't expect them to be duplicated within the near term in the 1632 universe.
Miscellaneous Up-Time Manufacturing Innovations
Optical glass must be homogeneous. Curiously, the importance of stirring the melt, so that the ingredients were efficiently mixed, was not recognized until 1790, when Pierre-Louise Guinand pioneered the use of a refractory ceramic stirring rod. (WBE, 218). This is one of those ideas which was long in coming, but was readily implemented.
It is also important to inhibit the formation of bubbles. This can be done by the addition of a fining (degassing) agent. Several are mentioned by the Encyclopedia Britannica (EB): arsenic oxide, sodium nitrate, sodium chloride, sodium sulfate and sodium nitrate (EB 300).
Early glass furnaces used wood as fuel. England needed the wood for shipbuilding, and, once the English figured out how to make a coal-fired furnace, they banned further use of timber (1610-1615). The new furnaces could achieve higher temperatures, which allowed for use of higher-melting glass compositions.
There is plenty of coal in the USE, but up-timers may find it advantageous to burn natural gas instead. It is readily available in the Grantville area, it is a more intense energy source, and it facilitates manufacturing. For automated feeding, the glass must have the correct viscosity, which in turn depends on temperature. It is easier to control the temperature of a gas-fired furnace. (Douglas, 42).
Important energy savings result from the use of a regenerator. Essentially, the flue (waste) gases are used to heat a brick "checker work" (shown in Fig. 4 of the Encyclopedia Britannica "Industrial Glass" article, and also discussed by the 1911 EB), which in turn is used to preheat the combustion gases. Heat regeneration was first used in the 1860s and reduced fuel consumption by about 90%.
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A major continuing expense for a pretwentieth-century glass factory was the pot used to hold the molten glass. In early nineteenth-century America, this pot cost about one hundred dollars, and took eight months to build from clay. It was able to resist the tremendous heat, but its life span was only eight weeks, and so the pots had to be replaced over and over again (Polak). Modern glass furnaces use highly refractory ceramics. (Different glass melts may necessitate different ceramics.) The Encyclopedia Britannica has two helpful comments on this point. First of all, it teaches that "clays of a high alumina-to-silica ratio, with minimal impurities," are more resistant. Secondly, it singles out the "electric-arc fusion-cast" ZAC refractory (35% zirconia, 53% alumina, 12% silica), developed in 1942.
Alumina is aluminum oxide. One major alumina ore, bauxite, is available in France and in Ireland. Please note that we aren't proposing to extract aluminum, but rather to use the bauxite, a claylike mineral, directly. A possible alternative to bauxite is kaolinite (aluminum silicate). According to the 1911 EB article on "kaolin," there is kaolinite "near Schneeberg in Saxony."
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Modern glassmaking operations employ a tank furnace. The raw materials are fed in at the loading end and the molten glass is removed from the working end. These tanks can be operated continuously, while pots process glass one batch at a time, which is less efficient. The first continuous furnace was constructed by Friedrich Siemens in 1867.
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While the Grantville Library provides critical information concerning both lead-alkali and borosilicate glass, the fact remains that quality control is going to be an ongoing problem. The mineral content of sands, ashes, and so forth are going to vary from source to source and even from lot to lot.
In the short term, USE glassmakers will keep careful records as to which raw materials were mixed together, in what proportions, to obtain a particular batch of glass, and the physical and chemical properties evidenced by that glass. If a particular batch does not pass muster for its intended purpose, it can be used for some less demanding task, or remelted. (A sign
ificant portion of the input to modern glass furnaces is rejected glass, called "cullet.")
The high school chemistry laboratory also should be capable of performing qualitative tests for some metals, using the standard flame and bead tests. I would expect the high school science teacher, Greg Ferrara, to know about these assays.
Grantville glass companies can make glass production more predictable by purifying the silica and the glass modifiers, so that the glassmakers know just how much of each ingredient they are adding to the melt.
Also, as the USE develops capabilities for production-scale inorganic chemical synthesis, it will be able to use alternative starting materials which are cheaper or more readily available. By way of precedent, the late eighteenth-century French government wanted to eliminate its dependence on Spain as a source of soda. (A Spanish seaweed, when burnt, provided an ash that was 20% soda.) The French offered a 2,400 livre prize, which was won by LeBlanc in 1787. LeBlanc synthesized a purified soda (sodium carbonate) from sea salt (mostly sodium chloride).
Improved Glass Products: Laboratory Glassware
Laura Runkle has pointed out that "in order to make pharmaceuticals, the people of Grantville need stainless steel, or glass-lined vessels." ("Mente et Malleo: Practical Mineralogy and Minerals Exploration in 1632," Grantville Gazette Vol. 2).
In 1632, Greg Ferrara commented, "Sulfuric acid is about as basic for modern industry as steel" (Chap. 40). Where, exactly, do you put sulfuric acid? Clearly, you need a corrosion-resistant vessel, whether that be glass, lead, or steel. If you want to play with hydrochloric acid, you need glass, a molybdenum-rich alloy, or tantalum.
For laboratory scale chemistry, glass is clearly superior to stainless steel and various exotic metals. Not only is it corrosion-resistant, it can be made transparent, so you can observe the chemical processes as they take place. Or it can be amber-tinted, to protect photosensitive chemicals. Glass is used extensively in the bottles, graduated cylinders, beakers, flasks, pipettes, condensers, test tubes, watch glasses, burets, funnels, crucibles, and retorts of modern chemical laboratories.
Borosilicate glass, such as that sold under the trademark Pyrex, is preferred, because it is especially resistant to acids, high temperatures, and sudden changes in temperature (thermal shock).
Improved Glass Products: Optical Instruments
Another form of specialty glass is optical glass. Dutch Admiral Maarten Tromp, awaiting the approach of the Spanish fleet, enviously remembers his brief experience with up-time optics: "The stunning visual clarity, featherlight weight, and exquisite craftsmanship of the binoculars had been convincing evidence of the marvels of which American artisans were capable." (1633, Chap. 19). King Gustav II Adolf of Sweden was equally impressed with Julie MacKay's spotting scope (1632, Chap. 48). And the nearsighted cavalryman Andrew Lennox appreciated his new American-made spectacles (1632, Chap. 16).
Like window glass, optical glass must be transparent. However, the real power of optical glass is realized when the glassware has a curved surface, creating a diverging or converging lens. Optical glass makes possible not only better spectacles and telescopes, but also microscopes. The latter is extremely important if medicine is to advance.
The preferred optical glass is a lead-alkali glass, which has a higher refractive index (a measure of the ability of the glass to alter the path of light which strikes its surface obliquely) than soda-lime glass.
Incandescent Light Bulbs and Fluorescent Light Tubes
Letting light escape, while keeping air from entering, is the function of the glass bulb of an incandescent light. The down-time master glassblower Hensin Hirsch is making light bulbs by hand, evacuating them using a vacuum pump scavenged from a refrigerator. (Gorg Huff, "Other People's Money," Grantville Gazette, Vol. 3). If the up-timers can duplicate the ribbon machines of our time line, then they can mass-produce light bulb shells.
In a fluorescent tube, the glass enclosure confines the mercury vapor. Electricity causes the latter to emit ultraviolet light, and this in turn stimulates a phosphor coating on the glass to absorb the light energy and re-radiate it as visible light.
Down-time glassblowers can certainly duplicate the tube itself, and mercury was available in 1632. The issues are how to inject the mercury safely, and how to obtain and apply the phosphor. I don't consider fluorescent lamps to be a practical development target for the USE, at least in the short-term.
Greenhouses
A logical extension of the normal architectural use of the window is the greenhouse, which has glass walls and ceiling. Greenhouses would allow the USE to grow plants that can only thrive under tropical conditions, or to obtain additional crops of plants that die back or become dormant in the northern European winter. Soon after the Ring of Fire, "medicinal and ornamental plants were [being] grown in the glass-roofed conservatory" of Grantville's hospital (Ewing, "An Invisible War," Grantville Gazette, Vol 2). If USE explorers venture into Latin America, they can bring back seeds of the Hevea brasiliensis rubber tree for greenhouse cultivation, and ultimate transplantation to a tropical country friendly to USE.
The concept of the greenhouse is not entirely foreign to seventeenth-century Europeans. De Serre protected individual plants by covering them with glass "bells" in 1600. There are also reports that orangeries with glass windows were established in Pisa (1591) and Leiden (1600) (Muijzenberg, 45). The greenhouse is quite practical if we can produce the necessary plate glass; "seconds" from the window glass factories would be probably be good enough.
Protective Glasses
Glass can be used in the windows of military vehicles and structures, but then we need to worry about the effect of enemy fire. A relatively low-tech way of reinforcing the glass is to use wire glass, which is sheet glass buttressed with a wire netting. Wire glass is made by lowering a wire mesh into a stream of molten glass. (Or by laying down a ribbon of glass, then the wire mesh, then another ribbon, and finally rolling them together.) Wire glass won't keep out a cannonball, but it will give some protection against, say, flying debris.
We should also be able to learn how to make tempered glass. The glass is heated to a high temperature and then cooled rapidly. The process increases the strength of the glass several fold, and also alters how it breaks; it powders, rather than forming dangerous shards. The duplication of tempered glass is a matter of determining, whether by library research or experiment, the necessary parameters, such as tempering temperature and cooling rate.
Both auto windshield "safety glass" and "bulletproof" glass are actually laminates of glass and plastic, and therefore must await the creation of a plastics industry.
Fiberglass
One of the largest twentieth-century markets for glass is in the manufacture of fiberglass. Coarse glass fibers were made and used in pre-Roman times, but merely for decoration of tableware. In 1870, John Player developed a process for mass producing a glass wool, useable as insulation. A fire-retardant cloth, with interwoven silk and glass fibers, was announced by Herman Hammesfahr in 1880.
Grantville's Encyclopedia Britannica briefly describes a method of making fiberglass in which the liquid glass enters a spinning, perforated cup, the fibers are extruded through the holes, and blasts of air fragment the fibers. Another approach, set forth in the World Book Encyclopedia, is to melt glass marbles in a furnace with a perforated bottom, and collect the threads onto a spinning drum. The tension created by the pulling drum helps draw out fine glass fibers.
The USE should be able make simple glass wools and cloths, but fiberglass composites, such as those used in the hull of the speedboat Outlaw, require a mature plastics industry.
Military Mirrors
There are some military uses of mirrors which were not well established in 1632, but which could now be exploited by the USE. These include the following:
Periscopes
The trench periscope, used extensively in World War I, was invented by the Polish astronomer Johannes Hevelius (1611-1687) in 1637. The first na
val use of the periscope was in the American Civil War, where one was improvised by Chief Engineer Thomas Doughty of the Union ironclad USS Osage during the Red River campaign of April 1864. (A periscope would have come in handy during the Monitor-Merrimac engagement, as Captain Worden of the Monitor was blinded when a shell struck near the viewing slit of the pilot house.)
Heliographs
In essence, the heliograph communicates coded messages in the form of light flashes. The principal advantage of the heliograph over the electrical telegraph has been that it could be used even in hostile territory, where a telegraph wire had not yet been laid, or was likely to be cut. This is not a problem with radio communications, but the number of radio sets in the USE is limited. The heliograph was used to great advantage by the British in Afghanistan and in the Boer War, and by the Americans in the Indian Wars.
The Indian tribes had countered the electrical telegraph by cutting telegraph wires and poles; the mirror telegraph was much less vulnerable to enemy action. The Apaches understood the significance of the heliographs all too well; they avoided the territory crisscrossed by the heliograph network. (Rolak).
