Abstract: Boron-free and fluorine-free glass compositions are provided that have properties of liquidus temperature, softening point and tensile strength similar to those of "E" or "621" glass compositions. These boron-free glass compositions have in percent by weight the following components:______________________________________ SiO.sub.2 55-61 Al.sub.2 O.sub.3 12-18 MgO 4-10 CaO 14-18 Na.sub.2 O 0.1-1.5 Li.sub.2 O 0.1-1.5 BaO 0.0-1.0 ______________________________________The compositions may also have minor amounts of Fe.sub.2 O.sub.3, TiO.sub.2, and K.sub.2 O. The glass compositions may be only boron-free and may have a minor amount of fluorine.

Abstract: A glass composition suitable for use in manufacturing glass fibers is described which possesses good electrical properties. The glass is characterized by having a boron oxide content below normal glass fiber glass and increased alkaline earth metal oxides with small quantities of magnesium oxide being present. The glasses produced by the composition have acceptable viscosities in the glass fiber making range and exhibit good stability to devitrification. Opacity is not encountered with these glasses as would be expected.

Abstract: Novel glass fiber forming compositions are disclosed having a reduced fluorine level. These compositions substantially reduce emissions of fluorine containing gas from glass furnaces when the batch is melted. Lithium oxide is added to the novel composition to reduce the softening point and liquidus temperatures of the composition. The resultant composition is found to be a highly desirable glass which when melted can be used to produce glass fibers having excellent tensile strength.