To provide a washing method preventing damage of a metal mask by contacting a supercritical or subcritical fluid, and dissolving, extracting, and recovering an organic EL material adhered to the metal mask.

A method is found for washing the metal mask by using the supercritical and/or subcritical fluid. Since recovery is easy and reuse is possible of the supercritical and/or subcritical fluid to be used, a modifier added to the fluid, and the organic EL material which is organic matter, the metal mask is washed efficiently without discharging environmental pollutant.

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