Patent ID: 7648656

Claim:
A method of making a polarizing glass composition, said method comprising the steps of: preparing a base glass having a composition comprising 20-60 wt. % SiO 2 , 12-20 wt. % Al 2 O 3 , 10-25 wt. % B 2 O 3 , and 15-40 wt. % Ag; adding to the above composition at least one noble metal salt selected from the group consisting of Pt, Pd, Rh, Au, Os, Ir and Ru salts, said noble metal salt being added in an amount in the range of 0.0025 wt. % to 0.5 wt. % measured as zero valent metal; mixing the components and then melting them in a manner to achieve a glass having a viscosity less than 10 3 poise; forming the glass into a suitable shape that allows stretching of the encapsulated silver particles in the glass matrix; thermally conditioning the formed glass to remove residual stress; finishing the formed glass to a selected geometry and at least one of chemically and thermally treating the surface of the formed glass to remove or cure flaws or contaminants on the surface, the subsurface, or the surface and subsurface of the glass; suspending the glass in a furnace heated to a temperature such that the viscosity of the glass is in the range of 10 6 to 10 8 poise, said suspension being in a manner such that the suspended glass can be drawn; controlling the furnace temperature, downfeed rate and the pulling speed during draw such that an applied force greater than 3500 psi is used to elongate the silver particles; and drawing the glass under an applied force to thereby attenuate the size of glass form and induce stress in the glass to thereby stretch the silver particles within said glass.