TYMPAN n.
A frame covered with parchment or cloth, on which the blank sheets are put, in order to be laid on the form to be impressed. Tympan sheet (Print.), a sheet of paper of the same size as that to be printed, pasted on the tympan, and serving as a guide in laying the sheets evenly for printing. W. Savage.…
VELLUM n.
A fine kind of parchment, usually made from calfskin, and rendered clear and white, -- used as for writing upon, and for binding books. Vellum cloth, a fine kind of cotton fabric, made very transparent, and used as a tracing cloth.