| abstract |
The invention is nitrate-free method to manufacture a blue soda-lime-silica glass composition and improving the ultraviolet light absorption thereof while maintaining a high visible light transmission. The method comprises the steps of: adding colorants, during molten glass formation, consisting essentially of a manganese compound along with a cobalt compound, iron oxide and optionally titanium oxide to a soda-lime-silica base glass composition, and adding no sodium nitrate into the batch during molten glass formation, the materials are adding in quantities sufficient to form said blue glass composition having at a 4.0 mm. thickness: 477-494 dominant wavelength and 6-40% purity of excitation. The blue glass composition, by weight, comprises a base glass composition of: 68 to 75% SiO2, 10 to 18% Na2O, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% Al2O3, and 0 to 5% K2O, where CaO+MgO is 6 to 15% and Na2O+K2O is 10 to 20%; and colorants consisting essentially of: 0.4 to 2.0% total iron oxide as Fe2O3, 0.15 to 2.00% manganese oxide as MnO2; 0.005 to 0.025% cobalt oxide as Co, and 0 to 1.00% titanium oxide as TiO2. The glass is useful for automotive or architectural applications. The method preferably involves the use of a reducing agent like anthracite coal during melting operations. |