Method for applying reacted boron oxide layer to vitreous silica substrate

The method of applying a thin transparent layer comprising boron oxide to the surface of a vitreous silica substrate, wherein the applied layer comprising boron oxide is adhered to and reacted with the surface of said substrate, said method comprising:

• a. forming a partially hydrolyzed aqueous clear solution principally comprising boron alkoxide and silicon alkoxide and alkali metal compound of at least one of soluble sodium or potassium organometallic compound, the amount of said alkali metal organometallic compound in said solution being determined by replacing up to about 20 mole percent of the boron alkoxide of a silicon alkoxide and boron alkoxide solution having a silicon alkoxide to boron alkoxide molar ratio of from 0.02 to 0.25 with said alkali metal organometallic compound, with the atoms of boron in said replaced boron alkoxide approximating the total atoms of alkali metal in said replacing organometallic compound;
• b. applying the formed solution to the surface of the substrate to be coated;
• and
• c. heating the substrate and applied coating at a temperature of from about 500.degree. C. to about 1100.degree. C. for a sufficient time to liberate the hydroxyl and organic components from the applied solution and completely react the glass-forming residual constituents of said solution with the surface of said substrate.