An enclosure for a portable electronic device can include a titanium substrate defining a textured surface and a nominal surface. The titanium substrate can include a first region that extends above the nominal surface and a second region adjacent to the first region and extending below the nominal surface. A separation distance between an apex of the first region and a bottom of a trough defined by the second region can be at least 1 micrometer. A metal oxide layer can overlay the trough defined by the second region.