Abstract: Borosilicate glass weak in boric acid having a high chemical stability with an alkali resistance according to DIN 52 322 of LBK-Class 1, a thermal expansion .alpha..sub.20/300 between 4.0 to 5.3.times.10.sup.-6 K.sup.-1, a ratio .alpha.'/.alpha. of thermal expansion coefficients above T.sub.g (.alpha.') to below T.sub.g (.alpha.) of 4 to 8, a glass transformation temperature between 500.degree. C. and 600.degree. C., high radiation transmittance and a UV transmission .tau..sub.250 nm/1 mm of 0 to 70% or .tau..sub.300 nm/1 mm of 0 to 91% of the composition in percent by weight on oxide basis of: SiO.sub.2 >75; B.sub.2 O.sub.3 1 to <9; Al.sub.2 O.sub.3 3 to 6; Li.sub.2 O 0 to 4; Na.sub.2 O 0 to 8; K.sub.2 O 0 to 6; MgO 0 to 3; CaO 0 to 3; BaO 0 to 2; SrO 0 to 2; ZnO 0 to 3; ZrO.sub.2 0 to 3; SnO.sub.2 0 to 3; SnO 0 to 3; TiO.sub.2 0 to 2; CeO.sub.2 0 to 2; Fe.sub.2 O.sub.3 0 to 1; with SiO.sub.2 +B.sub.2 O.sub.3 >83; SiO.sub.2 :B.sub.2 O.sub.3 >8; SiO.sub.2 +Al.sub.2 O.sub.3 +ZrO.sub.2 >83; Li.

Abstract: The borosilicate glass has a UV transmission of at least 80% at a UV wavelength of about 254 nm for a borosilicate glass sheet thickness of 2 mm, a linear coefficient of thermal expansion, .alpha..sub.20/300, of 3.2 to 3.4.times.10.sup.-6 K.sup.-1, a hydrolytic resistance of class 1 and a composition in % by weight based on oxide of______________________________________ glass formers <96%, SiO.sub.2 from 79.0 to 81.0%, B.sub.2 O.sub.3 from 12.5 to 13.0%, Al.sub.2 O.sub.3 from 2.0 to 4.0%, alkali metal oxides >2%, ______________________________________wherein said alkali metal oxides include from 2.0 to 3.5% said K.sub.2 O and from 1.0 to 2.0% said Li.sub.2 O, ______________________________________ alkaline earth metal <0.3%, oxides + ZnO reducing agent 0.025 to 2%, and non-oxidizing fining agent 0 to 3%. ______________________________________The weight ratio of K.sub.2 O to Li.sub.2 O is from 2:1 to 1:1 in the borosilicate glass.

Abstract: An optical crown glass having a negative anomalous partial dispersion .DELTA.P.sub.g,F, a refractive index n.sub.d of greater than 1.52, an Abbe number .nu..sub.d of greater than 57, and a high UV transmission has a composition (in % by weight) 40-72 B.sub.2 O.sub.3, 9-31 Al.sub.2 O.sub.3, 0-15 SiO.sub.2, 0.1-0.5 H.sub.2 O, 0-12 Li.sub.2 O, wherein the total of R.sub.2 O (R=Li, Na, K, Rb, Cs) is 0-20 and the total of MO (M=Mg, Ca, Sr, Ba) is 0-30, and wherein the total of R.sub.2 O and MO is greater than 5, and the molar ratio between Al.sub.2 O.sub.3 and B.sub.2 O.sub.3 is 0.2-0.3 and the molar ratio between (R.sub.2 O+MO) and B.sub.2 O.sub.3 is 0.1-0.4.