When feeding such sheets to a cylinder press, much trouble may arise if the waves occur along the “gripper edge,” which is usually on the longer dimension of the sheet. In some instances the difficulty may be avoided by ordering paper with the grain running the long way of the sheet, which also offers another advantage in relation to securing close register, namely this: the area of the sheet in square inches will increase least through atmospheric expansion which occurs across the grain if the cross-grain dimension is the lesser. [Illustration: SUPERCALENDER STACKS, APPLETON COATED PAPER CO. For a description of the Supercalendering process, see pages 55 and 56.] CHAPTER NINE APPRAISING AND TESTING PAPER The appraisal of a specimen of paper differs from testing in that an appraisal comprehends the value of an object in relation to its usefulness and marketability, whereas testing is merely an arbitrary method of expressing the chemical or physical properties of the object. The knack of appraising can be acquired only through practical experience; and the ability to make tests is gained only by careful technical training. In the majority of cases a satisfactory appraisal may be given without chemical or physical tests, but these are cases when the superficial characteristics, such as color, finish, feel, etc., are the prime qualifications, and such considerations as fiber contents, freedom from impurities, exact tensile strength etc., are of negligible importance. Although experience, only, leads to the knack of appraising paper, certain points might be suggested with benefit to the beginner which would assist him to an earlier acquirement of the art. COLOR.--Color being a purely relative term as applied to the variations in so-called “white” papers, it is necessary to make comparisons with accepted standards of the various grades in order to arrive at conclusions. In common parlance, white papers may be described as natural, light natural, white, blue-white, pink-white. Natural papers are those in which a minimum of artificial coloring has been added, and the brilliancy of shade depends entirely upon the quality of the stock.