The pressure which the rolls exert on the bromoil print and the paper as they pass through must be absolutely even, at every point. In order to make the pressure more uniform than the rolls of even a good machine can give alone, it is necessary to imbed the print and the paper in a press-pack. This press-pack generally consists of two pressboards (hard, thick, glazed pasteboard), at the bottom, an ordinary pasteboard, a copper-plate blanket, that is a thick felt, and another ordinary pasteboard. On this pasteboard the bromoil print is laid, and on this the printing paper. On this printing paper there are now placed in order another copper-plate blanket, an ordinary pasteboard and finally two pressboards. Before, however, we pass a press-pack, thus prepared, through the rolls, it must be explained in fuller detail, which is best done from an actual example.
Let us assume that we have a print prepared as described in the chapter “[Bromoil Printing],” ready for transfer. Its size shall be 16 × 21 cm (6¼ × 8¼ in.). Our intention is to print this on paper of the dimensions of 30 × 40 cm (12½ × 16½ in.), and to surround it with a plate mark. As the size of the paper is 30 × 40 cm (12½ × 16½ in.), the four pressboards, the three ordinary pasteboards and the two copper-plate blankets should be cut exactly 32 × 42 cm.
The two pressboards are accurately superposed on a table and then the pasteboard and the blanket are placed on top. On the last, as already stated, another pasteboard is placed, which must, however, be previously marked with pencil guide lines, for on it are to be laid the bromoil, the paper and the plate-mark pattern. As we wish to surround the print, which is 16 × 21 cm, with a plate-sunk mark, we must cut a sufficiently large pressboard to impress this mark. Let us say we wish to surround our vertical print with a margin which shall be 1 cm (⅜ in.) wide above and right and left, but 2 cm (¾ in.) below, then we must cut the pressboard 18 × 24 cm (7½ × 9½ in.). When we have done this we mark on it with a pencil exactly the position of the 16 × 21 cm bromoil print. Now we find on the 32 × 42 cm pasteboard the position at which we wish to have the 18 × 24 cm pressboard just cut (as a rule this will be a little above the center), and fasten it there very lightly with library paste or mucilage. The 18 × 24 cm pressboard now lies on the 32 × 42 cm pasteboard. As the size of the paper is only 30 × 40 cm, this will leave a margin of 1 cm on all sides, and this future position of the paper should be accurately marked with the pencil on the pasteboard. Extreme care having been taken that all the lines are parallel and the measurements correct, we can now place in the press-pack the bromide print and the transfer paper, and proceed to print.
Fig. 2
A = pasteboard
B = the plate-mark pattern
C = the location guides for the transfer paper
D = the location guides for the bromoil print.