[D] See Herzberg table, page [64].
Seasoning.—This process of acquiring normal moisture is usually called “seasoning.” As paper is probably never turned off at its full normal moisture, it is most desirable that it should be allowed time to season. It is not unusual to have people speak of new paper being too “green.” This may not have been an uncommon condition of hand-made papers which were dried entirely naturally, but, so far as machine-dried paper is concerned, I doubt if it is ever too green, though it is frequently made too dry.
Conditions Beyond Absolute Control.—Believing it to be impracticable to leave the precise normal moisture in machine-made paper, I have deliberately refrained from classifying this difficulty with faults chargeable to manufacture, and the general recognition of this circumstance indicates the wisdom of ordering paper long enough in advance to permit of a period of seasoning. In fact, this phenomenon of expansion or contraction of cellulose fibers places difficulties originating from this source in the class of conditions beyond absolute human control, but a study and understanding of the subject will enable one to prevent, or at least to minimize, such troubles. It consequently becomes the business of the printer to inform himself as thoroughly as possible on the subject. Static electricity is an element beyond absolute control and the source of much trouble. Both phenomena could be controlled by proper atmospheric conditions in storage and press rooms, but it is an expensive matter to equip rooms and install the necessary apparatus. The amount of trouble arising from these elements is often sufficiently costly in time and material to warrant investigation as to the expense involved.
The least a printer can do is to maintain hygrometers in his pressroom so as to keep track of atmospheric variations, and be guided accordingly.
STATIC ELECTRICITY IN PAPER
Among the “paper troubles” due to conditions for which neither the paper-maker nor the printer is responsible, none is more bothersome than the presence of static electricity in paper. These static charges, which are created by friction either in the making or handling of paper, develop magnetic propensities in the sheets, causing them to behave in ways which seem nothing but freakish until their nature is understood. Some sheets stick together as if they were glued, while others appear repellent to one another. Likewise, they may act in the same manner toward the fly-bars of the press. It is next to impossible to “feed” sheets so charged, and there is every likelihood of the ink from one sheet offsetting to another.
Every one familiar with the magnet knows that there are in magnetism two poles, the positive and the negative; that two substances of opposite polarity attract one another, but that substances of the same polarity repel each other. Static electricity—or frictional electricity, as it is also called—exists both in positive and negative charges, and sheets of paper containing static charges are governed accordingly.
Paper, when dry, is an insulator to electricity, but when moist it becomes an excellent conductor. Consequently, too much drying in manufacture increases the likelihood of electrical troubles, because it makes the paper more retentive of electricity with which it may become charged.
Pure air is also an insulator of electricity, which finds its paths through the air by means of the dust particles in suspension. Moisture in the air forms a connection between the dust particles through which the electricity easily passes into the ground, but when the air is dry this medium is lacking, so that substances containing static charges are deprived of these channels of conductivity. Cold air can not hold so much moisture as warm air, so that its insulating properties are increased. It is, consequently, in cold weather when this sort of paper trouble is at its worst.
These facts suggest the first steps of prevention to take against static electricity. First keep the air in the pressroom warm, and, if necessary, increase its humidity. It is also advisable to keep the paper in a warm room, for it has often been noticed that paper coming cold into a pressroom gives much trouble.