vintage aluminum measuring cup. The text "DEMI-LITRE" engraved on the side indicates its capacity.  The term "demi-litre" is French for "half-liter".  The cup's capacity is \(\mathbf{500}\text{\ ml}\) or approximately \(\mathbf{16.9}\text{\ fluid\ ounces}\).  It appears to be made of durable, lightweight aluminum, consistent with commercial or farmhouse kitchenware of the past.  Similar items are often collected as rustic kitchen decor or historical artifacts.