Glass and glass ceramics comprising metal oxide concentration gradient

The invention relates to glass and glass ceramics comprising a metal oxide concentration gradient. Embodiments of a plurality of glass-based articles are disclosed that include a first surface and a second surface opposite the first surface, both defining a thickness (t) of about 3 mm or less (e.g., about 1 mm or less). The glass-based article also includes a stress profile, wherein all points ofthe stress profile between a thickness range from about 0 * t to 0.3 * t and greater than 0.7 * t include a tangent of less than about 0.1 MPa/micron or greater than about 0.1 MPa/micron. In some embodiments, the glass-based article includes a metal oxide concentration that is not zero, the metal oxide concentration varying along a range of at least a portion of the thickness (e.g., 0. T to about0.3. T). In some embodiments, the metal oxide or alkali metal oxide concentration decreases from the first surface to a point located between the first surface and the second surface and increases from the point to the second