Method of opacifying the surface of glass articles

Claim 1

THE METHOD OF OPACIFYING AT LEAST A PORTION OF THE SURFACE OF A GLASS COMPRISING ESSENTIALLY 55% TO 75% SIO2, THE INDICATED PROPORTION OF AT LEAST ONE ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF UP TO 2% LI2O, 5% TO 18% NA2O, AND UP TO 13% K2O, THE SELECTED ALKALI METAL OXIDE INCLUDING NA2O, THE TOTAL ALKALI METAL OXIDE CONTENT BEING 12% TO 18%, 2% TO 12% AL2O3, 0.005% TO 0.05% CEO2, 1.8 TO 3.0% OF ANALYTICALLY DETERMINED FLUORINE, AND THE INDICATED PROPORTION OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF 0.01% TO 0.2% OF ANALYTICALLY DETERMINED CHLORINE, 0.02% TO 0.4% OF ANALYTICALLY DETERMINED BROMINE AND 0.03% TO 0.6% OF ANALYTICALLY DETERMINED IODINE, THE ESSENTIAL CONSTITUENTS TOTALING AT LEAST 85%, WHICH COMPRISES INTRODUCING SILVER IN A CONCENTRATION OF FROM 0.0001% TO 0.3% INTO THE SURFACE OF THE GLASS BY BRINGING THE GLASS AND A FINELY DIVIDED MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILVER AND SILVER COMPOUNDS INTO CONTACT, AND HEATING THE GLASS AND THE SILVER-CONTAINING MATERIAL WHILE THEY ARE IN CONTACT TO EFFECT AN EXCHANGE OF SILVER FOR ALKALI METAL IN THE GLASS THEREAFTER HEATING THE GLASS TO A TEMPERATURE ABOVE ABOUT 550* C. FOR A PERIOD OF AT LEAST 15 MINUTES, COOLING THE GLASS BELOW ABOUT 500* C., AND REHEATING THE GLASS TO A TEMPERATURE NOT LOWER THAN ABOUT 100* C. BELOW ITS SOFTENING POINT UNTIL THE DESIRED DEGREE OF OPACITY IS DEVELOPED.

Claim 2

THE METHOD OF OPACIFYING AT LEAST A PORTION OF THE SURFACE OF A GLASS COMPRISING ESSENTIALLY 55% TO 75% SIO2, THE INDICATED PROPORTION OF AT LEAST ONE ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF UP TO 2% LI2O, 5% TO 18% NA2O, AND UP TO 13% K2O, THE SELECTED ALKALI METAL OXIDE INCLUDING NA2O, THE TOTAL ALKALI METAL OXIDE CONTENT BEING 12% TO 18%, 2% TO 12% AL2O3, 0.005% TO 0.05% CEO2, 1.8 TO 3.0% OF ANALYTICALLY DETERMINED FLUORINE, AND THE INDICATED PROPORTION OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF 0.01% TO 0.2% OF ANALYTICALLY DETERMINED CHLORINE, 0.02% TO 0.4% OF ANALYTICALLY DETERMINED BROMINE AND 0.03% TO 0.6% OF ANALYTICALLY DETERMINED IODINE, THE ESSENTIAL CONSTITUENTS TOTALING AT LEAST 85%, WHICH COMPRISES INTRODUCING SILVER IN A CONCENTRATION OF FROM 0.0001% TO 0.3% INTO THE SURFACE OF THE GLASS BY BRINGING THE GLASS AND A FINELY DIVIDED MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILVER AND SILVER COMPOUNDS INTO CONTACT, AND HEATING THE GLASS AND THE SILVER-CONTAINING MATERIAL WHILE THEY ARE IN CONTACT TO EFFECT AN EXCHANGE OF SILVER FOR ALKALI METAL IN THE GLASS THEREAFTER HEATING THE GLASS TO A TEMPERATURE ABOVE ABOUT 550* C. FOR A PERIOD OF AT LEAST 15 MINUTES, COOLING THE GLASS BELOW ABOUT 500* C., AND REHEATING THE GLASS TO A TEMPERATURE NOT LOWER THAN ABOUT 100* C. BELOW ITS SOFTENING POINT UNTIL THE DESIRED DEGREE OF OPACITY IS DEVELOPED.