US Patent 10206298 Witness layers for glass articles

Glass articles having a base layer formed of glass and having a first compressive stress, an adjacent compression layer formed in the glass and having a second compressive stress, and a witness layer formed in the glass adjacent the compression layer and having a third compressive stress. The first, second and third compressive stresses all differing from one another. The witness layer also having a higher index of refraction than an index of refraction for the base or compression layers. Methods for manufacturing and methods of quality control that include the use of the witness layer are also disclosed.