Page:Paper and Its Uses.djvu/78

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Many users of paper look upon that material as being perfectly inert and stable, always of the same quality, and any defect which may arise remediable only by changing the paper. Unfortunately, the printer who uses the paper for letterpress, lithographic, or ruling purposes, finds that paper is not unchangeable, and when work has to be registered upon the paper difficulties often arise, and exchange is not always possible.

The principal difficulties arise from stretching, cockling, creasing, from the surface lifting or picking, from the paper being out of square, from electricity contained in the paper, and from loose particles coming away from the paper in the form of fluff. In addition there are difficulties in getting colour to dry upon certain papers, and in obtaining a solid impression or continuous line from printed or ruled matter.

Reference to the chapter on machine-made papers will serve to give the clue to some of the difficulties, and may suggest the remedy. The pulp, diluted with a large volume of water, consists of innumerable fibres, their length being at least 100 times their diameter, and as is the case of all water-borne bodies travelling in a fast stream, they take up the position in which their length is parallel to the direction of flow. The side shake of the wire alters the position of some of the fibres, and although the alteration is permanent,