[2] Stoichiometric copper selenide is a zero-bandgap material with metal-like behavior.

[5][6][7] Copper(I) selenide is produced in situ to form a protective black coating on iron or steel parts in some cold-bluing processes.

[8] Bluing solutions that operate in this manner will typically be labeled as containing selenous acid or selenium dioxide.

Cu2Se occurs as two polymorphs: berzelianite[11] (isometric, more common) and bellidoite (tetragonal).

There are more natural Cu selenides to date, including umangite, Cu3Se2 and athabascaite, Cu5Se4.