VOL.2. No. 12
OPTICN. GLASS
1155
OPTICAL GLASS B~usm& Lorn OPTICAL CO., ROCE?FL$~BR, N. Y. Optical glass differsradically from other varieties, both in its properties and in its method of production, due largely to the f a d that glass for optical purposes is required in comparatively large, thick pieces, while ordinary glass is commonly used in thin sheets. Optical glass first appeared on a commercial basis as the result of Dolland's invention of the achromatic telescope objective in 1757, ordinary glass having been found so lacking in homogeneity as to be quite useless for lens work. From this point the manufadure of optical glass went through various stages of development by such men as Guinand, Utschneider, and Fraunhofer. The most distinctive advance in optical glass manufacture was instigated by Professor Abbe of Jena, Germany. He obtained the collaboration of Dr. Schott, and together they founded the institution of Schott 8zGenossen a t Jena, which resulted in a few years in the production of a whole series of new glasses which w a novel in composition and optical properties. In recent years, experiments were conducted in the manufacture of optical glass in America. In 1903 the Bausch & Lomh Optical Co., of Rochester, began experiments, but it was not until 1912 that the euterprise was gone into on a serious basis. The early efforts a t this plant
were not a t all auspicious, and most of the year, 1913 was devoted to the study of all available information regarding the makimg of glass, and conducting practical experiments with various k i d s of fuel. The war in Europe had the effect of stimulating these experiments, and in the winter of 1914 a special building was erected with two gas firing furnaces and one pot arch or smaller furnace, which is used for the preliminary heating of the pots. The first melt of barium crown glass in May, 1915, was purple in color and not usable In the third week of the same month, however, some light crown and dense flint glass was produced which could be used. During the following month light flint glass was also successfully produced, and experiments were begun on most of the other types in more common use. It must be said here, in all justice to those concerned and to the Government's agencies, that when America entered the war in April, 1917, one of the first objects of the Government's concern was a supply of optical glass. The Government authorities accordingly made a survey of the situation and found that of the several establishments a t that time contending with the problem, the Bausch & Lomb Optical Company was the only one actually producing satisfactory glass. As a result, the Council of National Defense suggested that the Geophysical Laboratory of the Carnegie Institution in Washington, D. C., which had been turned over to the government a t the outbreak of the war, establish a research laboratory .at our plant. The chief difficulty up to that time had lain in the high absorption of light in the glass produced. The government workers were instrumental in obtaining purer raw materials, with which this difficulty was overcome, and i t then became a case of trying out different methods of stirring and temperature control in order to produce glass of the highest quality. The problem of pots, or crucibles, was a very difficult one that had to he solved along with the solution of the manufacturing problems of optical glass. For this reason i t became necessary for the Bausch & Lomb Optical Company to build a separate building in which the manufacture of special crucibles was successfully undertaken. In this connection Dr. Bleininger, formerly of the Bureau of Standards, was an important factor, and i t was largely through his efforts that Bausch & Lomb developed suitable pots in which optical glass could he made. At the present time the Glass Plant of the Bausch & Lomb Optical Company is of such a size and capacity as to produce all of the optical and ophthalmic glass used in the manufacturing activities of that concern. The exhibit was composed of an optical glass display, showing chiefly three methods of producing lenses. The first method is the method which was used a t the beginning of the glass-manufacturing activities of the
VOL.2, No. 12
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PERMALWY
1157
Bausch & Lomb Optical Company. In this method the glass, from the rough chunk which is broken out of a of glass after having cooled, is reduced to the approximate form, shape, and size of a lens by a sawing and milling process. The second method, which was established or developed during the war, was by procuring the shape, form, and size of the lens by means of various pressings of the glass, heated to a plastic state. The third method exhibited showed the steps taken in the ophthalmic or spectacle lens glass manufacturing. This differs from the optical glass manufacturing in that the glass made in the same type of a crucible is poured in its liquid state onto a large steel table top and rolled into a huge sheet. This sheet is then cut up into smaller pieces to the weight of the lens to be made. These small squares are then heated to a plastic state and pressed into the approximate form and size of the lens desired. The exhibit also showed the various ingredients used in the manufacture of glass, including sand and salts.
