A frame over which is stretched parchment, cloth, or paper, on which the sheet to be printed is placed before being turned down upon the forme. An inner tympan fits into it, and between the two the blankets and paper are placed which act as a sort of pad between the platen of the press and the forme when the table is rim in.
A frame over which is stretched parchment, cloth, or paper, on which the sheet to be printed is placed before being turned down upon the forme. An inner tympan fits into it, and between the two the blankets and paper are placed which acts as a sort of pad between the platen of the press and the forme when the table is run in.
A pasteboard tympan is most suitable for wood-cuts, for perfectly new type, and for the best kinds of press work. It is not suitable for miscellaneous work, nor for heavy formes, nor for formes of mixed old and new type. If the overlaying is properly executed, a pasteboard tympan will enable the pressman to show a sharper edge and a more delicate impression of the type than is possible with any other. Although contrary to a common belief, it need not wear the type. In all cases, however, a paste-board packing compels a tedious and careful making-ready. If this is neglected it may prove very destructive to the type.
A woollen blanket is best adapted for old stereotype plates, for old typo that has been rounded on the edges, for posters with large wood-type, and for all common work which requires a firm, solid, dull impression. For such work a woollen blanket will enable the pressman to make ready a forme more quickly than any other, but it is injurious to new type, and does not give a fine and sharp impression.
Thick paper is much used for book work, and also answers well for script circulars and leaded formes. It does not serve so good a purpose with mixed old and new type, nor for table-work with unequal heights of brass rule, nor for mixed large and small type. It will prove most serviceable for open formes of new type.
The India-rubber cloth combines many good qualities not found in other tympans, having the density of pasteboard, the hardness and evenness of paper, and the flexibility of the blanket, combined with an elasticity peculiarly to its own. It is adapted to a greater variety of work than any other; posters, script circulars, news and book formes, stereotype plates, and old or new type, call be well printed with an India-rubber blanket.
When it is intended to make one tympan or packing answer for all kinds of work, the India-rubber blanket will be found decidedly superior to all others; but when very extra press work is wanted, the tympan must be particularly adapted to the forme of type.
There are formes for which none of these tympans are specially suitable. For such cases careful pressmen combine two or more together, as Welsh flannel over rubber, or thin rubber over paste-board or under paper. These, however, are exceptional cases, and only occur when very good press work is to be obtained from imperfect materials. Careful observation of the peculiarity of the impression given by each kind of tympan will better teach a pressman how to combine them to the best advantage than any arbitrary rule.—For mode of making a tympan, see Covering a Tympan.
The second edition did not have an entry for Covering a Tympan but doing so is covered in Making Ready a Forme.