Patented July 30, 1935 29009,764 @UNITED: STATIES PATEN@T @OFFI@CE;. 2,009,764 F'INING HEAT ABSORBING REDUCED GLASSES Robert H. Dalton, Coming, N. Y., assignor to Corning Glass Works, Corning, N. Y., a corporation of New York No Drawing. Original application July 30, 1932, Serial No. 627,102. Divided and this application January 15, 1934, Serial No. 706,777 5 Claims. (Cl. 106-36.1) T'his invention relates to the fining of glass and has for its object the fining of glass melts which have been reduced by the addition of batches therefor of reducing agents such as carbon, carbonaceous materials, zinc dust, and the like, herein referred to as reduced glasses. The above and other objects may be attained by practicing my invention which embodies among its features the addition to such glass 10 batches of a small amount of a substance containing bromine. Glasses reduced by the addition of carbon or carbonaceous materials are practically never perfectly fined and there has long been a need 15 for means for fining such glasses. Arsenic which isordinarily used as a fining agent is obviously without value in reduced glasses, because the successful use of arsenic for this purpose requires oxidizing conditions such as the presence of a 20 nitrate or the use of the higher oxide of arsenic. Moreover, it is sometimes difficult to obtain uniform reduction in glasses reduced by carbonaceous materials because the carbon, although initially uniformly distributed throughout the 25 batch does not readily dissolve in the glass when the bl'tch is melted but tends to segregate and rise to the top of the melt where it may be burned off or cause overreduction while the bottom part of the melt is insufficiently reduced. 30 I have discovered that substances containing bromine, such as bromides, bromates, and the like, are very efficient fining agents when added in small quantities to batches for reduced glasses. I have further found that substances con35 taini-ng bromine are of themselves mild reducing agents and inasmuch as they, for the most part, seem to dissolve readily in giass they tend to promote more uniform reduction throughout the melt than is possible through the use of carbon 40 alone. on account of their mild agtion they do not tend to produce the so-called "carbon amber" coloration and the use of an excessive amount, therefore, has no ill effect, although on account of expense I prefer to use not more than 45 2%, which I have found to be aanple for fining purposes. My invention is particularly valuable in fining the so-called heat absorbing glasses which contain ferrous iron and must be melted with strong 50 reduction. Heretofore, it has been practically impossible to fine such glasses and at the same time to maintain the proper heat absorbing efficiency. The foeowing batches with the results of their melting will illustrate the application of My invention to heat absorbing glasses: 5 A B Sand ------------------------------------ 335 335 Sodium carbonate ----------------------- 85 80 10 Borax --------------- -------------------- 126 125 Ferric oxide ------- ---------------------- 10 10 Carbon ---- ----------------------------- @6 @6 Potassi bromide ----------- Degreeuof mfming --------------- Nobu' b' bles. Heat transmission in 2 mm. th 6.3% 5.9% 15 Glass A, wwch contained carbon but no bromine, is an example of a prior heat absorbing gl ass. It was reduced as is shown by the, low heat transmission but was not fined. 20 Glass B is an example of the use of a bromine containing material in conjunction with a reducing agent in accordance with my invention. It was perfectly fined and its heat transmi.ssion, which is s,lightly lo,,ver than that of glass A, 25 apparently indicates that bromine materials in no way interfere with the reducing action of carbon. In fact, in the example cited the results are slightly better with bromide and carbon than with carbon alone. 30 Low expansion borosilicate heat absorbing lasses are particularly difficult to fine on ae9 count of their high melting points and relatively high viscosities at melting temperatures. By the addition of 1 to 2% of a material contain'mg 35 bromine to such glasses, I am able to fine them and stih retain their heat absorbing efficiency. I have found also that chlorine containing materials are not as efficient fining agents as materials containing bromine and, when intro- 40 duced into glasses in amount comparable to the amount of bromine material which I have fgund necessary to cause fining, the chlorine material tends to produce opal glasses, particularly in the case of low expansion borosilicates. I, there- 45 fore, make no claim to the use of chlorine materials for this purpose. In the following claims the ternis "reduced glass" and "reduced glasses" refer to glasses which are melted under reducing conditions, or 50

2 2,009,764 to glasses which result from melting batches that contain a reducing agent such as carbon or carbonaceous materials and in tMs connection broniine materials are considered to be reducing g agents. This application is a division of my original application filed July 30, 1932, Sr. No. 627,102. What I