Eye-piece
A circular disk of iron containing a central sheet of mica, usually placed opposite to each tuyere, on the wind-box of the cupola; its object being to permit a view of the inside through the transparent mica. It works on a pivot, so that if necessary it may be moved aside and access had to the inside of the cupola if it is desired to remove any accumulated slag from the tuyere. See CUPOLA; SLAG; TUYERE; WIND-BOX.