Much of the paper used in books today is made of wood. Wood is converted into paper-making material in three ways. In one, it is cut into convenient lengths, stripped of its bark and finely ground on grindstones, and bleached. The product is called ground wood pulp. The paper made from this pulp is hastily and cheaply put together, has little strength, and soon turns yellow and grows brittle. There is often added to ground wood before making it into paper, more or less sulphite or soda pulp, usually the latter, the product of another process of turning wood into paper-making material.

In the sulphite and soda processes the wood is freed of bark, cut into small pieces, and reduced to a pulp by being heated with water and chemicals under pressure in an air-tight steel tank or boiler. Sulphite and soda pulp, which get their names from chemicals used in reducing the wood to pulp, have longer and better fiber than ground wood pulp. In both processes certain means are used to whiten the fiber and free it from sap, gum, and other things which would prevent it from acting properly in the paper-making machine, or would tend to make it grow yellow or spotted. Spruce or basswood are the woods chiefly used, and they seem to submit themselves to treatment better and to give a longer fiber than other kinds. The pulp made from rags is often mixed with sulphite and soda pulp. The rag-pulp fiber improves the quality of the resulting paper for reasons not easily set forth. Paper made entirely of wood may be of good quality, especially sulphite papers. The popular outcry against wood paper is based on the fact that much of it is made very cheaply and poorly.

The rags used in paper making are nearly all cotton. They are not all of them rags in the ordinary sense of the term. Many of them are cuttings from clothing factories and have never been used. New rags do not act the same way under the treatment which changes them to paper pulp as do the old ones. The paper made entirely from new cloth differs somewhat from that made from old rags. The best book papers, however, contain only stock prepared from old rags.

The process of changing rags into paper is very similar to that of changing wood into paper. The rags are cleaned, freed from foreign substances, cut into small pieces, thoroughly washed, bleached, and then beaten to a pulp, under water, by machines which convert them into a soft, homogeneous, creamy mass, called technically stuff, and yet preserve the greatest possible length of fiber. This process of beating rags into good paper-making material requires care and considerable time. If the process is hastened unduly the resulting material is not so good.

Paper is made from other materials besides wood and cotton; but nearly all of that used in books in this country is made of one or other of these two materials, or of a combination of the two.

The stuff produced as described, almost milk-like in its consistency, is pumped from a tank, in which it is kept constantly stirred to prevent the fiber from settling, onto the paper-making machine. This machine is an evolution from a simple hand appliance which was used by paper makers for several centuries. It was a shallow tray with a bottom made of a network of wires. This was held in the hands, dipped into a vat containing the paper-making material, and as much of the latter taken up on the wires as in the judgment of the maker was sufficient for a sheet of paper. It was then shaken gently, and deftly handled, until the water, running through the wires, left on the latter, and spread evenly over them, a layer of fibers. These dried and matted together in a few seconds sufficiently to enable the maker to turn them out on a blanket; on this another blanket was spread, and on this was laid another layer of fibers. The skilful maker of paper by hand (in a few places in this country the craft is still practiced) can secure considerable evenness in the layers of fiber or pulp on the wire of his frame; but the layer is never of quite the same thickness throughout. Handmade paper can sometimes be distinguished by these variations in its thickness. Machine-made paper is of nearly uniform thickness. In the process of taking up from the vat by hand a thin layer of stuff, the maker wove together the fibers in every direction by skilful and delicate movements of the frame. A paper-making machine cannot so thoroughly interweave the fibers. Paper made by hand, therefore, has a quality which cannot be secured on a machine. This peculiar texture of handmade paper of the first class delights the connoisseur, and furnishes a printing surface superior, in some respects, to any machine-made paper.

The paper-making machine consists primarily of an endless roll of wire screen, similar to that forming the bottom of the shallow tray used in making paper by hand. This wire screen, stretched around rollers, travels almost horizontally away from a broad shelf from which it receives a stream of stuff pumped onto the latter from the tank before mentioned. As the pulp pours out onto this wire it settles over the screen, and is woven together by the latter’s oscillating and forward movement, and by the time it reaches the end of the screen is sufficiently matted and dry to hold its shape, the water being removed by suction. It is then picked up by a roller, and goes through a succession of rolls, varying in size, number, character, heat and pressure, according to the quality of the paper being made and the surface desired thereon. In some cases, toward the close of the process, it is passed through a tank containing a thin mixture of glue and water, called size, and then is again dried. Coming out as paper at the end it is cut into lengths and piled, or gathered on a roll.

The wire diaphragm onto which the paper pulp first pours, and during the passage over which it is worked into a mat, the water meanwhile being extracted from it, is of varying styles. If perfectly plain the resulting paper is almost without marks, and is said to be wove. If made of wires of different sizes properly arranged the paper, as it lies on it, receives deeper impressions from the larger wires than from the smaller and the former appear as light lines running through it when finished. Paper thus marked is called laid, to distinguish it from the wove. As the paper comes from the wires it passes under the dandy roll. This roll sometimes has figures or letters raised on its surface. These impress themselves on the soft paper and produce a greater transparency where they touch, sometimes reducing the thickness, and give the finished paper what is called a watermark. It is so called not because it is made of water or by water, but because it looks as though it were drawn on the paper with a point dipped in water.

Endless varieties of paper can be made from the same materials. It may contain more or less rag; may be beaten to a greater or less extent and with more or less care; may be spread thicker or thinner; may be rolled on hot rolls, or polished, more or less; may receive more or less sizing; may be dyed in a vat before it starts for the machine, or dipped in dye after it is made, or color may be applied to one surface by machine. The fiber may be carelessly produced, and the chemicals used in bleaching and cleaning it may be only partially neutralized, with the result that the paper will soon act as if being eaten with acid, and will rapidly turn yellow under a bright light.

The ordinary observer can distinguish between very poor and fairly good paper in books. He cannot distinguish between paper of fairly good quality and the best.

The paper used in newspapers is nearly all made entirely of ground wood. Most of it is made as cheaply as possible, and soon grows brittle and dark in color. This is of little consequence in most cases. For the ordinary newspaper the paper has served its purpose if it looks well for twenty-four hours after it is printed and exposed to the light.

Books are generally printed on paper which has not been very highly polished. Ink is taken from the type more readily by paper of this kind, especially if the latter be rather soft in texture, so that the press drives into it the face of the type bearing the ink. Modern processes of reproducing pictures give plates for printing, many of which are made up of very fine lines placed very closely together and having very shallow depressions between them. To print from these with good results the paper used must have a very smooth, highly polished surface. The press drives soft paper down into the narrow places between the fine lines and blurs the impression of the cut. Newspapers which use process-cuts of the kind mentioned are obliged to use paper with a smooth surface to get good results. This smooth surface is generally produced, as already noted, by passing the paper between hot metal rollers, a process called calendering. In a more expensive process, called plating, the paper, cut into sheets, is laid between sheets of zinc until a pile of several inches in thickness is formed, and this pile is passed several times under rollers exerting a heavy pressure. This smooths, polishes and hardens the paper. Much of the paper used for illustrations in books has a surface made by applying a coating of clay or other material to it and then polishing it. Quite good results can be obtained with fine line cuts on calendered or plated paper without the addition of a coating of clay. The illustrations on coated paper which are found in books are very commonly printed separately from the book itself, which is on ordinary uncoated paper, and inserted separately. Generally these inserts are not carefully fastened in and cause much annoyance by falling out after the book has been subjected to a little use.

Recently paper makers have succeeded in producing a paper which has a smooth surface without the high polish usually found on that which is coated, or highly calendered. The polished surface of these papers, especially of the coated, is very objectionable to readers, light being reflected from it in an unpleasant way.

It will be seen from what has been said that it is difficult so to describe what we may call good book paper that it can be readily distinguished. Constant study and careful comparisons of the papers one meets in books will enable one to judge of them with some success. One who has much to do with books should take note of the paper of which they are made, and learn to distinguish between poor and good, and the good and the best, as far as possible. This is especially desirable for one whose work with books includes their rebinding and repairing. Coated paper breaks easily, the stiffening added to it by the coat of clay giving it a tendency to fall apart as soon as it has been folded in the same place a few times. Soft and fragile paper, such as is found in many books, will stand very little wear at the joint in the back. Paper not carefully bleached and freed from the chemicals used in bleaching, rapidly discolors at the edges where exposed to light. Such facts as these, and many others, will be found useful when one comes to have books rebound, or attempts to repair them.

That side of the paper which touched the wires on which it is made is different from the other. This difference is usually visible to the trained eye. It is often taken into consideration in fine printing.

As the pulp flows out upon the wires it tends to mat together more thoroughly along the line of flow than across it. This gives paper a grain, along which it tears and folds more readily than across it. This fact also is often taken advantage of in good printing.

All paper expands or stretches when wet. This is to be kept in mind in mending books. An added strip, pasted on, usually draws and wrinkles, when it dries, the paper to which it is applied. Hence the rule, in mending, to use thick paste and apply the pasted sheet or strip to its place as quickly after pasting as possible.

Mr. Chivers has recently made, 1909, with the help of chemists and other experts, a very careful examination of the composition, structure, tensile and folding strength and other qualities of the paper now used in several thousand popular books. The results of this examination, when applied to the subjects of book-selection and book-buying, will be of great value to libraries. The quality of the paper used in the books on which libraries spend a large per cent. of their book fund—novels—is the question that should be first considered in selecting editions. Libraries may hope soon to be able to select editions much more wisely than heretofore. The investigations by Mr. Chivers, and those carried on by U. S. Government experts in Washington, will not only enable libraries to discover the best editions for purchase, but will also enable them to secure bindings so carefully adapted to the quality of the paper in each book as to give that book the longest possible life of usefulness.