Recent complaints about the quality of paper and the rapid decay of manuscripts and papers have resulted in arousing some interest in the subject of the durability of paper used for books and legal documents, and in the equally important question of the ink employed. The Society of Arts and the Library Association in England and the Imperial Paper Testing Institute in Germany have already appointed special committees of inquiry, and from this it is evident that the subject is one of urgent importance.

It is sometimes argued that the lack of durability is due to the want of care on the part of manufacturers in preserving the knowledge of paper-making as handed down by the early pioneers, but such an argument is superficial and utterly erroneous. The quality of paper, in common with the quality of many other articles of commerce, has suffered because the demand for a really good high-class material is so small. The general public has become accustomed to ask for something cheap, and since the reduction in price is only rendered possible by the use of cheap raw material and less expensive methods of manufacture, the paper of the present day, with certain exceptions, is inferior to that of fifty years ago.

The causes which favour the deterioration of paper are best understood by an inquiry into the nature of the fibres and other materials used and the methods of manufacture employed.

The Fibres Used.—Cotton and linen rags stand preeminent amongst vegetable fibres as being the most suitable for the production of high-class paper capable of withstanding the ravages of time. This arises from the fact that cotton and linen require the least amount of chemical treatment to convert them into paper pulp, since they are almost pure cellulose, cotton containing 98·7 per cent. of air-dry cellulose, and flax 90·6 per cent. The processes through which the raw cotton and flax are passed for the manufacture of textile goods are of the simplest character, and the rags themselves can be converted into paper without chemical treatment if necessary. As a matter of fact certain papers, such as the O. W. S. and other drawing papers, are manufactured from rags without the aid of caustic soda, bleach, or chemicals. The rags are carefully selected, boiled for a long time in plain water, broken up and beaten into pulp, and made up into sheets by purely mechanical methods.

The liability of papers to decay, in respect of the fibrous composition, is almost in direct proportion to the severity of the chemical treatment necessary to convert the raw material into cellulose, and the extent of the deviation of the fibre from pure cellulose is a measure of the degradation which is to be expected. The behaviour of the fibres towards caustic soda or any similar hydrolytic agent serves to distinguish the fibres of maximum durability from those of lesser resistance. It may be noted that in the former the raw materials, viz., cotton, linen, hemp, ramie, etc., contain a high percentage of pure cellulose, while in the latter the percentage of cellulose is very much lower, such fibres as esparto, straw, wood, bamboo, etc., giving only 40-50 per cent. of cellulose. The two extremes are represented by pure cotton rag and mechanical wood pulp. Other things being equal, the decay which may take place in papers containing the fibre only, without the admixture of size or chemicals, may be considered as one of oxidation, which takes place slowly in cotton, and much more rapidly with mechanical wood pulp. Experimental evidence of this oxidation is afforded when thin sheets of paper made from these materials are exposed to a temperature of 100° to 110° C. in an air oven. The cotton paper is but little affected, while the mechanical wood pulp paper soon falls to pieces.

The order of durability of various papers in relation to the fibrous constituents may be expressed thus: (1) rag cellulose; (2) chemical wood cellulose; (3) esparto, straw, and bamboo celluloses; (4) mechanical wood pulp. The rate and extent of oxidation is approximately shown by the effect of heat as described. The differences between the celluloses are also shown by heating strips of various papers in a weak solution of aniline sulphate, which has no effect on wood or rag cellulose, dyes esparto and straw a pinkish colour, and imparts a strong yellow colour to mechanical wood pulp and jute.

Physical Qualities.—The permanence of a paper depends not only upon the purity of the fibrous constituents and the freedom from chemicals likely to bring about deterioration, but also upon the general physical properties of the paper itself. Other things being equal, the more resistant a paper is to rough usage the longer will it last. The reason why rag papers are so permanent is that not only is the chemical condition of the cellulose of the highest order, but the physical structure of the fibre is such that the strength of the finished paper is also a maximum.

The methods of manufacture may be modified to almost any extent, giving on the one hand a paper of extraordinary toughness, or on the other hand a paper which falls to pieces after a very short time. Thus a strong bank-note paper may be crumpled up between the fingers three or four hundred times without tearing, while an imitation art paper is broken up when crumpled three or four times.

A thorough study of the physical qualities of a paper is therefore necessary to an appreciation of the conditions for durability. The physical structure of the fibre, the modifications produced in it by beating, the effect of drying, sizing, and glazing upon the strength and elasticity of the finished paper, are some of the factors which need to be considered.

Strength.—The strength of a paper as measured by the tensile strain required to fracture a strip of given width, and the percentage of elongation which the paper undergoes when submitted to tension, are properties of the utmost importance. The elasticity, that is, the amount of stretch under tension, has not received the attention from paper-makers that it deserves. If two papers of equal tensile strength differ in elasticity, it may be taken for granted that the paper showing a greater percentage of elongation under tension is the better of the two.

The strength of a paper, as already indicated, is greatly influenced by the conditions of manufacture. This has been explained in the chapter devoted to the subject of beating, and other examples are briefly given in the following paragraphs.

Bulk.—The manufacture during recent years of light bulky papers for book production has accentuated the problem in a marked degree, and the factor of bulk as one of the causes of deterioration is therefore a comparatively new one. It is interesting to notice that the rapid destruction of such books by frequent use is in no way related to the chemical purity of the cellulose of which it is composed, or to the influence of any chemical substance associated with the fibre. It is purely a mechanical question, to be explained by reference to the process of manufacture.

This paper is made from esparto entirely, or from a mixture of esparto and wood pulp. The pulp is beaten quickly, and for as short a time as possible, little or no china clay being added, and only a very small percentage of rosin size. The wet sheet of paper is submitted to very light pressure at the press rolls, and the bulky nature is preserved by omitting the ordinary methods of calendering.

The paper thus produced consists of fibres which are but little felted together. The physical condition and structure of the paper are readily noticeable to the eye, and when these peculiarities are reduced to numerical terms the effect of the conditions of manufacture is strikingly displayed.

The effect of this special treatment is best seen by contrasting the bulky esparto featherweight paper with the normal magazine paper made from esparto. In the latter case a smoother, heavier, stronger sheet of paper is made from identically the same raw material. But the pulp is beaten for a longer period, while mineral matter and size are added in suitable proportions. The press rolls and calenders are used to the fullest extent.

The difference between these two papers, both consisting, as they do, of pure esparto with a small proportion of ash may be emphasised by comparing the analysis by weight with analysis by volume. The two papers in question when analysed by weight proved to have the following composition:—

But if the papers are compared in terms of the composition by volume, it will be found that the featherweight contains a large amount of air space.

In other words, the conditions of manufacture for the bulky paper are such that the fibres are as far apart from one another as possible, and the cohesion of fibre to fibre is reduced to a minimum.

While paper of this description is agreeable to the printer, and probably to the general reading public, yet its strength and physical qualities, from the point of view of resistance to wear and tear, are of the lowest order. It is very difficult to rebind books made from it, which is not altogether to be wondered at, seeing that the bookbinder's stitches can hardly be expected to hold together sheets containing 60 to 70 per cent. of air space.

This concrete case emphasises the necessity for including in a schedule of standards of quality a classification of papers according to strength and bulk.

Surface.—The introduction of new methods of printing has brought about some changes in the process of glazing and finishing paper which are not altogether favourable to the manufacture of a sheet having maximum qualities of strength and elasticity, two conditions which are essential to permanence. In other words, the very high finish and surface imparted to paper by plate-glazing, supercalendering, water finish, and other devices of a similar character is carried to excess.

All papers are improved in strength by glazing up to a certain point, but over-glazing crushes the paper, renders it brittle and liable to crack. Unfortunately, the maximum strength of a paper is generally reached before the maximum of finish, with the result that the former is frequently sacrificed to the latter. The usual result of glazing is found in an increase of 8 to 10 per cent. in the tensile strength, but a diminution of elasticity to the extent of 8 to 10 per cent. With supercalendered magazine papers, the high surface is imparted for the sake of the illustrations which are produced by methods requiring it. The addition of considerable quantities of clay or mineral substances improves the finish, so that the question of the relation of glazing to strength, surface, and loading is one which affects the subject of deterioration of paper very materially. With writing paper the false standard of an “attractive” appearance is almost universally accepted by the public as the basis of purchase without any reference to actual quality.

Mineral Substances.—China clay, sulphate of lime, agalite and other inert mineral substances are important factors in lowering the quality of paper, not so much in promoting the actual deterioration of paper by any chemical reaction with the fibres, as in making the paper less capable of resistance to the influence of atmospheric conditions and ordinary usage. Clay in small, well-defined quantities serves a useful purpose, if added to some papers, because it favours the production of a smooth surface, but when the combination of mineral substances is carried to an extreme, then the result from the point of view of permanence is disastrous. This is well recognised by all paper-makers, and in Germany the limits of the amount of clay or loading in high-grade paper have been rigidly fixed. In the case of imitation art paper, which contains 25 to 30 per cent. of its weight of clay, the strength and resistance of the sheet is reduced to a minimum. The paper falls to pieces if slightly damped, the felting power of the fibres being rendered of no effect owing to the weakening influence of excessive mineral matter. This paper is used chiefly for catalogues, programmes, circulars, and printed matter of a temporary and evanescent character, and so long as it is confined to such objects it serves a useful purpose, being cheap, and suitable for the production of illustrations by means of the half-tone process; but its lasting qualities are of the lowest order. The addition of 10 per cent. of any mineral substance must be regarded as the maximum allowance for papers intended for permanent and frequent use.

Coating Material.—The ingenious method for producing an absolutely even surface on paper by the use of a mixture of clay or other mineral substance and an adhesive like glue or casein brushed on to the surface of the paper, is responsible for many of the complaints about the papers of the present day.

The sole merit of this substance is the facility with which half-tone process blocks can be utilised for the purpose of picture production. Beyond this, nothing can be said. The paper is brittle, susceptible to the least suspicion of dampness, with a high polish which in artificial light produces fatigue of the reader's eye very quickly, heavy to handle, and liable to fall to pieces when bound up in book form.

As the fibrous material is completely covered by mineral substances, it is frequently considered of secondary importance, with the result that the “value” of the paper is judged entirely by the surface coating, with little regard to the nature of the body paper. In such cases, with an inferior body paper, the pages of a book very quickly discolour, and the letterpress becomes blurred.

Analysis of a Typical Art Paper.

Rosin.—The presence of an excess of rosin is a well-known factor in the disintegration of the paper, even when the fibrous composition is of the highest order. The decomposition is largely due to the action of light, many experiments having been made by Herzberg and others to determine the nature of the reactions taking place. One of the chief alterations is the change brought about in the ink-resisting qualities of the paper.

The actual character of the chemical reactions as far as the effect on the fibre is concerned is not accurately known. The degradation of a hard-sized rosin paper by exposure to strong sunlight, for example, is probably due to the alteration in the rosin size, and not to any material change in the cellulose. It is hardly conceivable that in a pure rag paper sized with rosin and yielding readily to ink penetration, after about one year's exposure to light, the cellulose itself had undergone any chemical changes capable of detection.

Gelatine.—Papers properly sized with gelatine are preferable to those sized with rosin for the majority of books and documents preserved under normal circumstances. But the nature of a tub-sized paper may be, and often is, greatly altered by unusual climatic conditions. In hot, damp countries papers are quickly ruined, and high-class drawing papers sized with gelatine often rendered useless. The change is scarcely visible on the clean paper, and is only observed when the paper is used for water-colour work, the colour appearing blotchy in various parts of the sheet where the gelatine has been decomposed by the united action of heat and damp.

The artist is frequently compelled in such cases to put a layer of heavy white colour on the sheet of paper before proceeding to paint the picture.

The storage of books under favourable conditions has a great deal to do with the permanence of the paper, and the degradation of a paper in relation to the tub-sizing qualities is much hastened by the presence of moisture in the air.

Starch.—The same is true of starch, which is largely employed as a binding or sizing material in paper. The degradation of gelatine, starch, and similar nitrogenous substances is due to the action of organisms, and the following experiments, suggested by Cross, are interesting in this connection.

If strips of paper are put into stoppered bottles with a small quantity of warm water and kept at a temperature of about 80° F., fungus growths will be noticed on some of them after the lapse of fourteen days. Rag papers sized with gelatine will show micro-organisms of all kinds. A pure cellulose paper, like filter paper, will not produce any such effects. The result in the first case is due to the nitrogenous substance, viz., the gelatine used in sizing, since the two papers are identical as far as the cellulose fibres are concerned. High-class wood pulp papers, unless sized with gelatine, would not show similar results. The action of the organisms upon the nitrogenous material by a process of hydrolysis is in the direction of the production of soluble compounds allied to the starch sugars capable of being assimilated by organisms.

The cellulose of esparto and straw are readily attacked, and it is on this account that the tissues of the various straws are digested more or less when eaten by animals. It is for this reason that the celluloses from straw and esparto are inferior to the cotton cellulose in producing a paper likely to be permanent.

Chemical Residues.—The necessity for manufacturing a pure cellulose half-stuff is fully recognised by paper-makers. This was not the case in the early days of the manufacture of wood pulp, for it is a matter of common experience that many of the books printed on wood pulp paper between 1870 and 1880 are in a hopeless condition, and it is quite easy to find books and periodicals of that date the pages of which crumble to dust when handled. This serious defect has been proved to be due to the presence of traces of chemicals used in manufacture which have not been thoroughly removed from the pulp.

The precautions necessary in bleaching pulp by means of chloride of lime, in order to prevent (1) any action between the fibre and the calcium hypochlorite, (2) the presence of residual chlorine or soluble compounds derived from it, and (3) the presence of by-products arising from the use of an antichlor, are also well known to paper-makers. The subject has been closely studied by chemists, who have shown that the deterioration of many modern papers may be ascribed to carelessness in bleaching.

The questions relating to the chemical residues of paper can only be adequately dealt with by a discussion of actual cases which arise from time to time. There are certain conditions in manufacture, common to all papers, which may give rise to the presence of chemical residues, of which two have already been mentioned.

The acidity of papers is frequently quoted as an instance. It is true that the presence of free acid in a paper is most undesirable, as it seriously attacks the cellulose, converting it into an oxidised form. This in course of time renders the paper so brittle as to destroy its fibrous character.

The change is brought about by the acid, which itself suffers no material alteration, so that the process of deterioration is continued almost indefinitely until the cellulose is completely oxidised. Most papers, however, show an acid reaction when tested with litmus, the usual reagent employed by those not familiar with the proper methods of testing paper. All papers which have been treated with an excess of alum for sizing purposes would show an acid reaction with litmus without necessarily containing any free acid.

The presence of iron is undesirable, particularly in photographic papers, and since cellulose has a remarkable affinity for iron, the conditions of manufacture which tend to leave iron in the pulp have to be taken into consideration. The presence of minute quantities of iron in the form of impurities must not be confused with the presence of iron in large quantities derived from the toning and colouring of paper by means of iron salts.

The fading of colour is frequently observed when coloured papers are tested on boxboards, particularly those made of straw. This fading may often be traced to the presence of alkali in the straw board which has not been completely removed in the process of manufacture.

The blurring of letterpress is a defect which often occurs with printing papers made of chemical wood pulp. The oil in the ink seems to separate out on either side of the letter, producing a discoloration. In such cases the paper itself frequently exhibits an unpleasant smell.

These defects are usually determined by the presence of traces of sulphur compounds in the paper resulting from incomplete washing of the pulp in manufacture. The presence of sulphur compounds sometimes associates itself with papers which have been coloured by means of ultramarine, which in presence of alum is slightly decomposed by the heat of the drying cylinders.

Some knowledge of the effect of chemical residues in paper is important, not only in regard to the deterioration which takes place in the fibre itself, but also in relation to the fading of the ink which is used. The subject of the ink has received much attention from chemists on account of the serious difficulties which have been experienced by State departments in various countries.

The United States Department of Agriculture have devised certain methods for ascertaining the suitability of stamping ink used by the Government and suggest the qualities desirable in such an ink. The ink, first of all, must produce an indelible cancellation; that is, it must be relatively indelible as compared with the ink used for printing the postage stamps. The post-mark made with the ink must dry quickly in order that the mail matter may be handled immediately without any blurring or smearing of the post-mark.

Both this property and the property of the indelibility involve the question of the rate at which the ink penetrates or is absorbed by the fibre of the paper. A satisfactory ink does not harden or form a crust on the ink-pad on exposure to air. There must be no deposition of solid matter on the bottom of the vessel in which the ink is stored, and the pigments on which the indelibility of the ink depends, if insoluble, must not settle out in such a way as to make it possible to pour off from the top of the container a portion of the ink which contains little or none of the insoluble pigment or pigments.

Colour.—If the subject of deterioration of paper is to be considered in its broadest sense as including changes of any kind, the fading of colour must be taken into account. The use of aniline dyes which are not fast to light results in a loss of colour in paper just as with textiles, and the fading may be regarded as a function of the dye and not as arising from its combination with the paper.

The gradual fading of some dyes, however, and of many water-colour pigments may be traced to the presence of residual chemicals in the paper and to the presence of moisture in an atmosphere impregnated with gaseous or suspended impurities. In fact the latter is a greater enemy to permanence of colour than light, since it has been proved by experiment that most colours do not fade when exposed to light in a vacuum. The oxygen of the air in combination with the moisture present is the principal agent in bringing about such changes. The dulling of bronze, or imitation gold leaf, on cover papers is a practical illustration of this, though this can hardly be quoted as an instance of actual deterioration of the paper.

The maintenance of the original colour can only be assured by the careful selection of pure fibrous material, the use of fast dyes, and the preservation of the book or painting from the conditions which favour the fading as described above. For common papers such precautions become impossible, but for water-colour drawings and valuable papers they are essential.

The demand for an abnormally white paper is indirectly the cause of deterioration in colour, but in this case the ultimate effect is not a fading but a discoloration of white to a more or less distinct yellow or brown colour, due to changes in the fibre which may often be traced to excessive bleaching. In this case the fading of colour is directly due to deterioration of the paper itself, and may occur in celluloses of the best type. With lower-grade papers containing mechanical wood pulp the degradation of colour and fibre is inevitable.

Air and Moisture.—The exact effects produced on paper freely exposed, or in books as ordinarily stored, depend upon the condition of the atmosphere. Pure air has little or no action upon paper, cellulose being a remarkably inert substance, and even in impure mechanical wood pulp, if merely exposed to pure dry air, the signs of decay would be delayed considerably. The combined action of air and moisture is of a more vigorous character in promoting oxidation changes in the fibres, or a dissociation of the sizing and other chemical ingredients of the paper. The presence of moisture is, indeed, absolutely essential for the reaction of some substances upon one another, and it is easy to show that certain chemical compounds can be left in ultimate contact, if absolutely dry, for a lengthened period without reacting, but the addition of a little moisture at once produces chemical union. This may be shown by a simple experiment.

Thus a piece of coloured paper which may be bleached immediately if suspended in an atmosphere of ordinary chlorine gas will remain unbleached for several hours if first thoroughly dried in an oven and exposed to dry gas.

In the case of books and papers, these conditions which promote slow disintegration are aggravated by the presence of impurities in the air, such as the vapours of burning gas, the traces of acidity in the atmosphere of large manufacturing towns, the excessive dampness and perhaps heat of a climate favouring the growth of organisms. All these factors are of varying degrees in different places, so that the deterioration of papers does not proceed in the same measure and at the same rate everywhere.

Moisture.—It may not be out of place to discuss some important relations between moisture and the physical qualities of a sheet of paper. A paper in its normal condition always contains a certain proportion of water as one of its ingredients, and the presence of this moisture has much to do with the strength, elasticity, and use of the paper, the absence of moisture giving rise to defects and troubles in the use of the paper which to a certain extent lower its commercial value and deteriorate it, though not perhaps in the sense of permanent degradation of quality.

One trouble frequently experienced by stationers and others is that known as wavy edges. The edges of a stack containing sheets of paper piled upon one another frequently twist and curl, producing what are known as wavy edges. This arises from the fact that the paper when manufactured was deficient in natural moisture, and that when stacked it has gradually absorbed moisture, which is taken up first by the edges exposed to the air. This causes unequal expansion of the fibres with the production of the so-called wavy edges. The only remedy in such cases is the free exposure of the sheets before printing, so that the moisture is absorbed equally all over the sheet. The cracked edges of envelopes may be explained by reference to the same conditions. The paper is worked up into envelopes in an over-dry condition, and the fibres, being somewhat brittle, readily break apart from one another. If the paper is kept in stock for some time before use this defect can be very largely remedied.

With supercalendered papers it is only possible to obtain the best results by allowing the paper to stand for several days after making before it is glazed.

It is evident from these few examples that many of the troubles experienced by printers are due to the fact that orders for paper are frequently accompanied by an instruction for immediate delivery, under which circumstances it is impossible to obtain the best results. The expansion of papers used for lithography, and the bad register frequently seen in colour work, may be explained by reference to the behaviour of the individual fibres towards moisture. The expansion is usually greater in one direction of the paper than in the direction at right angles to it, and this is due to the fact that fibres have a greater ratio of expansion in the diameter than in the length.

The behaviour of papers when damped is a peculiarity well known to paper-makers and printers. For certain purposes it is desirable that paper should not show any material alteration when damped, since any expansion of the sheet is liable to throw the printing out of “register.” The liability of papers to such stretch or expansion is largely minimised by careful manipulation of the pulp during the process of beating, and also by a proper regulation of the web of paper as it passes from the wet end of the paper machine over the drying cylinders to the calenders. The paper which fulfils the necessary qualifications as to a minimum stretch is prepared from pulp which has not been beaten for too long a period, so that the pulp obtained is fairly light and bulky. By this means the expansion of the fibres takes place in the sheet itself without making any material alteration in its size. That is to say, as the sheet of paper is fairly open, there is sufficient room for expansion, which thus takes place with the least alteration of the total area of the sheet. The paper which is allowed to shrink on the machine during the process of drying, without undue tension, usually exhibits a minimum amount of expansion subsequently in printing.

It is important to notice that the expansion of paper is different for the two directions, that is for the machine and cross directions.

This arises from the fact that in the machine-made paper the greater proportion of the fibres point in the direction of the machine while the paper is being made. In consequence of this the expansion of the paper is greatest in what is known as the cross direction of the paper, that is, in the direction at right angles to the flow of the pulp along the machine wire.

This is to be explained by reference to the behaviour of fibres when damped or brought into contact with an excess of water. The question of the exact changes in the dimensions of a fibre due to absorption of water has been dealt with in an interesting manner by Hohnel. He points out that the well-known peculiarity of the shrinkage of ropes which have been lying in the water can be explained by an examination of the behaviour of the single fibres. He relates in detail the experiment which can be carried out for the exact observation of the fibres when in contact with water. A dry fibre when soaked in water appears to become 20 to 30 per cent. greater in diameter, whereas in length it is usually only increased by one-tenth per cent.

The method adopted by Hohnel was to place a fibre of convenient length on a glass slip down the centre of which was a fine narrow groove capable of holding water, so that the fibre could be wetted. Over the fibre was a cover glass with a small scale marked on it. The loose end of the fibres passed over a small roller and was stretched by a light weight. The movements of the fibre were measured by means of an eye-piece micrometer.

In this way it is possible to determine alterations in length to within 0·005 per cent., and this variation can be directly seen under the microscope.

Hohnel observes in his account of the experiments that all fibres become thicker when wetted, that vegetable fibres are more susceptible than animal fibres.

Animal fibres expand about 10 to 14 per cent. in diameter, but vegetable fibres as much as 20 per cent., as shown in the following table:—

The reverse is the case when the expansion of the fibres in regard to length is considered, since animal fibres expand 0·50 to 1·00 per cent. of their length, and vegetable fibres only 0·05 to 0·10 per cent.

The maximum amount of expansion in the case of the vegetable fibres is obtained by gently breathing upon them rather than by the use of an excess of water.

These figures are important as explaining many of the peculiar characteristics of vegetable and animal fibres. Advantage is taken of the greater expansion of the latter in the manufacture of instruments for the measurement of moisture, such as the hair hygrometer, in which the elongation of a stretched hair registers the variation in the moisture of the atmosphere.

Quality of Book Papers.—The Committee of the Society of Arts in dealing with the evidence as to the permanence of finished papers suggest the following classification as indicating the desired standards of quality:—

(A) Classification as to Fibres.

A. Cotton, flax, and hemp.

B. Wood celluloses, (a) sulphite process, and (b) soda and sulphate process.

C. Esparto and straw celluloses.

D. Mechanical wood pulp.

The Committee find little fault with the Principles which govern the trade in the manufacture of high-class papers, and limit the result of their investigation to the suggestion of a normal standard of quality for book papers required in documents of importance according to the following schedule:—

Fibres.—Not less than 70 per cent. of fibres of Class A.

Sizing.—Not more than 2 per cent. rosin, and finished with the normal acidity of pure alum.

Loading.—Not more than 10 per cent. total mineral matter (ash).

With regard to written documents, it must be evident that the proper materials are those of Class A, and that the paper should be pure, sized with gelatine and not with rosin. All imitations of high-class writing papers, which are in fact merely disguised printing papers, should be carefully avoided.

These recommendations are good as far as they go, but in order to establish the proper standards of quality some specifications must be laid down with regard to the strength of the paper and its physical properties, together with a reference to the use for which the paper is intended. The physical condition of the paper itself apart from the nature of the fibre has much to do with its resistance to wear and tear, and this is easily proved by comparing modern book papers made from esparto with book papers of an earlier date made from the same material.

The only official schedule of requirements in relation to public documents is that issued by the Stationery Office.

The details set out relate chiefly to questions of weight and strength, the limits being expressed in definite form and not allowing much margin for variation in respect of strength or fibrous constituents. Mechanical wood pulp is excluded in all papers except common material as stated in the schedule. The papers required for stock are divided into twelve classes. In each class the trade names of various sized papers are given, the size of the sheet and the weight of the ream, and, where required, any special characteristics are set out. The schedule is as follows:—

Class 1. Hand-made or Mould-made.

General Specification.—Hand-made or mould-made. Animal tub-sized. (“Hand-made” or “Mould-made” to be marked on the wrapper.)

Where special water-marking is required mould will be supplied by the Stationery Office for those papers made by hand.

Class 2. Writings, Air-dried.

General Specification.—Plate rolled. Machine made. Animal tub-sized. Air-dried. (Must bear ink after erasure.)

Note.—The mean breaking strain and mean stretch required are given for each paper. The figures represent the mean of the results obtained for both directions of the sheet, and are calculated on a strip of paper five-eighths of an inch wide and having a free length of seven inches between the clips.

Class 3. Writings, Ordinary.

General Specification.—Rolled. Machine-made. Animal tub-sized.

Class 4. Writings, Coloured.

Specification.—Highly rolled. Machine-made. Animal tub-sized.

Class 5. Blotting Papers.

Specification.—All rag. Machine-made. Free from loading.

Class 6. Printing and Lithographic Papers.

General Specification.—Rolled. Machine-made. Engine-sized. Loading not to exceed 15 per cent.

Class 7. Coloured Printings.

General Specification.—Rolled. Machine-made. Engine-sized.

Class 8. Copying and Tissue Papers.

Specification.—Machine-made. Free from loading. (Copying papers are required to give three good copies.)

Class 9. Brown Papers, Air-dried.

Specification.—Air-dried. Machine-made.

Note.—The mean breaking strain and mean stretch required are given for each paper. The figures represent the mean of the results obtained for both directions of the sheet, and are calculated on a strip of paper two inches wide and having a free length of seven inches between the clips.

In the case of papers indicating a larger breaking strain than the minimum required, a proportional increase in the stretch must also be shown.

Class 10. Brown Paper, Cylinder-dried.

General Specification.—Machine-made.

Note.—The mean breaking strain required is given for each paper. The figures represent the mean of the results obtained for both directions of the sheet, and are calculated on a strip of paper two inches wide and having a free length of seven inches between the clips.

Class 11. Smallhands.

General Specification.—Machine-made. Engine-sized.

Class 12. Buff Papers.

Specification.—Highly finished both sides. Machine-made. Hard engine-sized.

Mechanical wood pulp must not be used in the manufacture of any papers, with the exception of engine-sized coloured printings, and buff papers, where an addition up to 25 per cent. will be allowed.

All animal tub-sized papers are required to be as far as possible free from earthy matter; and, except where specially stated, the amount of loading added to other papers must not exceed 6 per cent.

When sulphite or soda pulps are used, either separately or conjointly, in the manufacture of printing papers, the quantity of neither material shall separately exceed 50 per cent.

The most complete specification as to the requirements for standard papers is that published by the Paper Testing Institute in Germany, and used as the basis of most contracts, at least for public and official documents.

Standards of Quality in Germany.—The classification of papers according to the raw materials used and the nature of the finished paper is very complete. The classification is made under three headings: (A) Raw Material; (B) Strength; (C) Uses.

(A) Classification according to Material.

(1) Paper made from rags only (linen, hemp, and cotton).

(2) Paper made from rags with a maximum of 25 per cent. of cellulose from wood, straw, esparto, manila, etc., but free from mechanical wood pulp.

(3) Paper made from any fibrous material, but free from mechanical wood pulp.

(4) Paper of any fibrous material.

(B) Classification according to Strength.

The tests for tearing length, resistance to folding, elasticity, etc., are made in air showing relative humidity of 65 per cent. The calculations for tearing length are made on strips of paper dried at 100° C.

(C) Classification according to Use.