Removing silicon species from hydrocarbon solvents such as cyclohexane by flowing the hydrocarbon solvent through a selective adsorbent selected from the group consisting of aluminas, silicon-aluminas, ion exchange resins, zeolite Y, and combinations thereof. The mask is attached to a moveable carrier. The heel inclination visually recognizing part, which is formed on the heel side of the face surface, formed by a visible boundary between a heel side region of the face surface and a center region of the face surface, can be visually recognized to be inclined to the heel side from the toe side in a direction toward the sole side from the top side. The first characteristic is an insufficient thickness to function as an etch stop layer, and the second characteristic is an insufficient selectivity to etchants employed to etch through the first layer to function as the etch stop layer.