The nature of the fiber brings about a difference, in that some fibers have thicker walls and smaller canals than others. The treatment causes a variation, in that a quick beating with sharp knives leaves the fibers more nearly in their original shape than a prolonged beating with dull knives, which breaks down the structure of the fibers and draws them out into minute fabrillæ. The strength of a paper of given quality will also to a certain extent be proportionate to the duration of beating, as well as the amount of pressing and calendering received. The amount of sizing and the drying also affect its strength. An antique paper, having large air spaces and loosely knit as it is, has not the tensile strength it would possess if pressed and calendered to a greater density. The addition of loading adds to the weight without increasing the strength, as it has no binding properties. Moreover, the bulk, in proportion to the weight, is lessened by the introduction of filler. Consequently it is axiomatic, that of two given papers of equal weight, finish and quality of fiber, the one containing the less filler will be the stronger, as well as bulkier. The addition of filler, however, increases the opacity, gives mellowness, and improves the printing quality by equalizing the texture of the surface. The addition of sizing tends to increase the strength of paper, owing to its adhesive properties, but if liberally used it detracts from the mellowness and gives the sheet a tinny “character.” The length of the fiber also affects the strength, as long fibers give greater strength and better folding quality than short. It is not possible to get as close formation with long as with short fibers. Hence occasions frequently arise wherein customers ask for characteristics which are somewhat contradictory. A desires a light, bulky paper with a high finish, but a bulky paper with high finish must, in the nature of things, be heavy. B desires a very strong, thin, but opaque paper. It is obvious that the strength of a thin, opaque paper can be but a relative factor, while thinness and opacity are irreconcilable features. C inquires for a closely formed sheet, with good folding qualities, but the first characteristic is only to be gained at the expense of the latter. D wishes to print half-tones on an antique paper. In this case modern printing inventions have bridged over some of the obstacles of the past, and the offset press and extra-deep engravings have brought this last requirement within the realms of possibility, but unless resort is had to these new methods, the requirements again are irreconcilable to each other. It is evident, however, that only through technical paper information can one solve such problems as necessitate a compromise capable of giving the maximum possible satisfaction.