Packing.—Occasionally troubles may be charged to faulty packing—cases too loosely packed when stood on end permit the paper to sag, thus causing a curling tendency at one end of the sheets.
The use of unseasoned case lumber or cases and inferior case lining give access to moisture, the effect of which is discussed herein at length.
The susceptibility of coating to picking may be determined by applying hot sealing wax. If the wax after cooling is pulled off with only the coating adhering it may be assumed that a “tacky” ink would work the same, whereas if the paper tears out with the wax—it proves conclusively that the coating is well sized.
Coated-paper Troubles.—Coated papers have their characteristic shortcomings. The picking of small particles of the coating is perhaps the most common fault, and is caused by insufficient adhesive elements in the coating mixture. Other troubles are traceable to some of the defects of the body stock. Irregularity of the finish is sure to come from faulty application of the coating or careless calendering. Grit or bubbles in the coating is likely to result in a porous surface. The sour odor of some coated papers is due to decomposing casein or glue.
Casein used as an adhesive in most coated papers is a product from skim milk. It contains lactic acid which must be neutralized in preparing the coating mixture. For this purpose an alkali such as soda or ammonia is used, and when properly handled the coating should be neutral. An alkaline coating will cause re-etching on lithographic plates or stones.
Starch coatings or combinations of starch and casein are cheaper than full casein and do not yield as high a finish and when improperly used have often been the cause of picking.
The Printer’s Responsibility.—The second group of difficulties, or those for which the printer is to blame, may originate with the improper storage of the paper. As pointed out, the standing of cases on end is conducive to wavy paper. Dampness is a prime cause of trouble, as will be sufficiently shown later on, but it is elementary to say that paper should never be exposed to moisture.
Engravings.—The troubles of ignorant or inefficient pressmen and foremen are often laid to the paper, especially where half-tone printing is involved. In the first place, too little attention is given to securing proper originals for the half-tones. Retouching is omitted in a fit of false economy, for at this very stage of the game it was never truer that “An ounce of prevention is worth a pound of cure.” Too much care can hardly be given to securing good engravings.
Secondly, the selection of a proper half-tone screen is frequently overlooked. While no hard-and-fast rules may be set, the best one, when in doubt, is to include with the engraver’s order a sample of the paper on which the cuts will be printed. He can judge, taking into consideration the subject and the stock, which screen is advisable. In general, it may be affirmed that 120 or 133 line screens are best for uncoated smoothly finished papers, and 150 or 175 line screens are most satisfactory for coated stock.
Inks.—Next comes the suitability of the ink, and there again the ink manufacturer’s advice, always available, is often neglected; but experience proves that certain papers yield best results with certain inks. Such matters can only be determined by actual experience, but when in doubt consult the ink-man.