Strengthened glass and methods for making using differential density

An article of manufacture, the article comprising:

• a chemically strengthened substrate characterized by having a glass chemical structure including alkali ions situated in the glass chemical structure
• wherein the substrate has dimensional volumes including
• a treatment-rich volume including a rich surface of the substrate,
• a treatment-poor volume including a poor surface of the substrate and characterized by having a variation from the treatment-rich volume in at least one of a chemical composition and a chemical structure, and
• a bulk volume, within the substrate, adjacent at least one of the treatment-rich volume and the treatment-poor volume,
• wherein a concentration of metal in at least one of the treatment-poor volume and the treatment-rich volume is ≧about 0.4 mole % higher than a concentration of the metal in the bulk volume,
• wherein a concentration of the metal is higher in the treatment-poor volume than a concentration of the metal in the treatment-rich volume, and
• wherein a concentration of alkali ions in a diffusion depth of at least one of the treatment-rich volume and the treatment-poor volume is ≦about 0.5 mole % higher than a concentration of the alkali ions in the bulk volume.

An article of manufacture, the article comprising:

• a chemically strengthened substrate made by a process including
• providing a substrate characterized by having
• a glass chemical structure comprising host alkali ions having an average ionic radius situated in the glass chemical structure, and
• wherein the substrate has dimensional volumes including a treatment-rich volume and a treatment-poor volume located as opposed to each other in the substrate,
• providing an exchange medium characterized by having an areal density of invading alkali ions having an average ionic radius that is larger than the average ionic radius of the host alkali ions
• wherein the areal density is associated with an ion exchange rate of the invading alkali ions,
• providing a modified exchange medium characterized by having a modified areal density of the invading alkali ions
• wherein the modified areal density is associated with a modified ion exchange rate that is slower than the ion exchange rate,
• applying the modified exchange medium to a surface of the treatment-rich volume;
• applying the exchange medium to a surface of the treatment-poor volume;
• and
• conducting ion exchange while applying at least one of the exchange medium and the modified exchange medium to produce the strengthened substrate.