The half stuff consists of water and a cellulose material, the fibres of which are separate from one another and in convenient short lengths. In preparing this half stuff it is important that no pulping or beating of the fibre should occur until it is quite clean, or the dirt present will become absorbed in the hydrated cellulose which will be formed and will thereafter remain permanently in the paper produced. The natural fibrous cells may be long, i.e., several millimetres, as they are in cotton, hemp, flax, ramie, and in the operation of preparing half stuff they will have been reduced in length, by cutting under the knives of the breaker : if, on the other hand, the natural fibrous cells are short, i.e., no more than two or three millimetres, as they are in wood and esparto, this cutting becomes superfluous, and breaking of them is therefore omitted. But some degree, at least, of compression bruising and comminution will be required, and hence, beating can never be omitted, except for very low grade products and such special products as cable papers. These operations of breaking and beating, therefore, produce combined effects of separating the fibres from one another, reducing their length in appropriate degree, and of bending, softening, bruising, flattening, and hydrating them, and it is possible to adjust this processing to give any desired combination of these effects and thus to modify the qualities of the resulting paper in any de sired degree between the extreme limits of quality, characteristic of a paper of blotting paper type on the one hand, and of a paper of banknote and cigarette paper type on the other hand, in the latter of which the individual or ultimate fibres are beaten out of all recognition under the microscope. The manner of the adjust ments required to give such variously proportioned effects is determined not only by the methods of breaking and beating employed, but also by the structural characteristics of the fibres themselves : each fibre has, in fact, its own characteristics, which the skilled paper maker bears in mind in making his adjust ments. To make a strong paper it is necessary to subordinate cutting to bruising : in these circumstances the ends of the lengths of fibres, cotton, hemp, flax, ramie, are broken, splayed and tangled, and this increases their felting and strengthening quali ties. Sometimes they are split longitudinally into fibrillae; and cotton fibrillae, thus formed, may display an interlacing net or trellis work appearance ; the flax and hemp fibre on the other hand, frequently split into bundles of fibrillae to give a paint brush appearance. The hydration effect, consequent on the bruis ing action of the beater, which leads to imbibition of water, is more easily produced in some fibres than in others : flax and hemp fibres easily hydrate, then always have a slimy feel, and are easily distinguished, in the hand, from cotton, which has not the same tendency. If the material has been beaten to work wet, which may take as much as twelve hours and more of beating, a considerable quantity of water may be retained by the material on the paper-making wire : the material then undergoes the more shrinkage in drying, and the finished paper has considerable rattle and hardness. The texture is also more closed, less porous and the amount of sizing required to give suitable ink-resistant quality is relatively small. (See PAPER MATERIALS.) The breaking and beating effects are contrived by adjustment of the angles of the knives on the bed plate and on the revolving drum : the greater the angle of inclination the more rapid is the cutting effect productive of reduced lengths of fibre : the lower the angle of inclination the greater is the slower bruising action. This is the fundamental distinction between breaking and beat ing, though in actual practice breaking is frequently part of a combined operation that includes also washing and bleaching : a breaker is for this purpose and is therefore provided also with a drum washer, which is a wire gauze drum, revolving in the chan nel, and from its interior water can be continuously removed and simultaneously can be replaced by fresh water, fed in just in front of the breaker roll, so as to keep the pulp concentration at the more or less constant value required, which will be usually about 3-5%, otherwise a breaker and a beater are similar.
If half stuff, less or more beaten, is made direct into paper it gives, therefore, a product having qualities which may range from those of blotting paper to those of bank note paper. A number of other finishing operations, additional to breaking and beating, are employed to give special qualities of surface : these operations are those of colouring, sizing, loading and calendering. The sub stances used in these auxiliary operations are of course selected in relation to their cost and to the effects that can be derived from their use. For sizing, gelatine and rosin, with alum, are the materials much the most commonly used, though very many other substances have been or are used in much smaller degree, such as casein, starch, silicate of soda (the more acid brands are preferred), soaps (with alum), and viscose. For loading, the sub stances in common use are china clay (kaolin) and "pearl harden ing" (calcium sulphate). Other substances have been or are used in lesser degree and for special purposes : e.g., certain magnesian
substances such as agalite (nearly pure magnesium silicate, akin to asbestos in composition and properties), French chalk, and soapstone assist the paper in taking a highly finished surface, which is a characteristic effect of using magnesian minerals, probably referable to their "soapy" nature : "heavy spar" (barium sulphate) is used particularly for the surface loading of photo graphic papers. It is usual, except in making papers of the very highest quality, to add to the pulp in the beater a small quantity of relatively cheap mineral loading material, such as china clay or "pearl hardening." This is not to be regarded as merely an adulteration, since it serves to fill up the pores of the paper and to make a closer texture, more evenly absorbent of printers' ink, and it allows a better surface to be obtained by simple calendering : most important of all, it increases opacity, and thus enables the manufacturer to provide cheap papers that can be satisfactorily inscribed on both sides. If added in large propor tion, mineral loading of course greatly diminishes the strength of the paper, and particularly its powers of resisting the wear and tear of folding. The colouring of paper is effected by the addi tion of pigments or solutions of dyestuffs to the pulp in the beater. (See p. 233.) The production of definitely coloured paper is small, but the majority of papers receive some admixture of colouring matter, added with the object of correcting an otherwise objectionable tint. Thus even bleached pulps always re tain a residual yellow tint, more or less pronounced, but an appar ently good white can be prepared therefrom by the addition of appropriate quantities of red and blue to produce what is really a satisfactorily balanced grey. The successful production, in this way, of an approved illusion of whiteness with such low grade materials as mechanical and unbleached bisulphite wood pulp, containing up to 70% and more of the former, in modern news print, is a considerable industrial achievement : the fact that, in newsprint, it is .short lived does not diminish the achievement.
The inchoate pulp slurry may be transformed into the cohesive dry sheet, either by hand or by machine, to make the so-called "hand made" or "machine made" paper. Paper making may therefore be divided conveniently into two portions : (a) the treatment of the primary raw material as far as the point at which it is in the condition of pulped cellulose half stuff, ready for the paper making operation proper, and (b) the transforma tion of the pulped cellulose slurry thus formed into paper by the paper making process proper, with the auxiliary optional treat ments of colouring, sizing, loading and calendering.
The expense of making paper by hand is so great that only papers for special purposes and of the highest quality are now "hand made": they are always made from "all rag" pulps of the finest quality, and they are used for such special purposes as artists' water-colour drawing papers, bank ledgers, bank notes, important documents and the highest class of printed books. The pulp from the beater is run into stuff chests from which the vats are supplied, before reaching which it is strained to ensure uniformity and removal of any adventi tious ingredient. The sheet of paper is then made on a mould of wire-cloth, which has a removable frame of wood surrounding it, to keep the pulp from running off the edges while the super fluous water is running away through the meshes of the wire cloth: this removable frame is called the "deckel." The craftsman dips the mould, with the deckel in position, into the vat and lifts out enough of the pulp to make just one sheet of paper of the required thickness: as soon as the mould is removed from the vat the water begins to drain away and to leave the fibres on the surface of the wire to form a cohesive sheet : a lateral motion or "shake" given to the mould by the craftsman, assists the "felting" of the fibres and ensures their lying in all directions. The "deckel" is then removed from the mould and the mould is inverted on to and pressed against a felt, whereby the sheet is transferred or "couched" from the wire to the felt. A number of sheets, thus formed, are then piled one above another, with inter leaving felts, and submitted to strong pressure to remove water : and after subsequent removal of the felts, the sheets are again pressed and dried, and matured and are then ready for sizing by dipping in a tub of gelatine solution—"tub sizing." Any "water mark" pattern or name required on the sheet is obtained by fasten ing the wire water-mark design to the surface of the wire mesh, which is thereby embossed to give the design of the water-mark: consequently less pulp lodges there and the paper is by so much the thinner on the lines of the water mark which thus produces in the paper the exact counterpart of the water mark wire pattern. Hand made papers are sometimes made which are extremely hard and water resistant. A high proportion of flax linen, up to 8o per cent, which hydrates very readily, gives thus a hard paper, and its water resistant quality can be further increased by "hard sizing" with gelatine containing a high proportion of alum.