Sheets of waste paper that are used upon the tympan sheet, to prevent the ink setting-off on the sheets that are successively printed when the reiteration is working; they are changed as soon as any setting-off is perceptible. They are slipped under the points at their edges, and are quickly changed, or turned, which is always done to economize the use of paper.
Set-off Sheets are also used upon the cylinders of machines that perfect, for the same purpose.
A sheet of thin paper is interleaved between every impression of fine work, particularly if it be large heavy paper and large type, to prevent setting-off in the heap; the work is hung up to dry with these sheets in, which are taken out by the warehouseman before the work is piled away, who then knocks them up, folds them in quires, and takes care of them till they are wanted again by the Pressmen.
Paper for these purposes is supplied by the warehouseman, who gives for the first waste or spoiled impressions; for the other tissue paper is generally used, and with care it will last a long time.