LEATHER
The most expensive materials used in covering books and those which vary most in quality are leathers, the skins of animals which have been tanned and made flexible. The best bookbinding leathers are those which are flexible both in the skin and on books, and the surface of which is not easily damaged by friction. Owing to the many kinds of leathers and their variation in quality, it is difficult to learn to know them well.
The skins of all sorts of animals have been used for covering books. Certain ones, not suitable for library binding, are still used for the purpose in various parts of the country, so that librarians need to become expert in their knowledge of which leathers may be employed and which ought to be rejected.
Variations in the same kinds of leathers are caused by:
(a) Age. Skins of animals which have not reached full growth should not be used for binding library books. Since they are immature, the fibres have not become tough, and they have not reached their maximum thickness. If the skins which the binder is using are exceptionally small, it is probable that the animals from which they were obtained were too young. On the other hand, the skins of very old animals should not be used, since the fibres of the skins have lost something of their flexibility and strength. They cannot be readily detected, but they are sure to give poor service. As an illustration of the effect which age has upon leather it will be sufficient to note the well-known fact that calf skin is useless for library purposes, while cowhide within certain well-defined limits is exceedingly useful.
(b) The sex of the animal. It has been proved beyond question that the skin from the female of some animals, notably goats, does not wear as well as that from the male.
(c) Country from which they come. It is an interesting fact that the skin of a sheep which comes from Persia is not the same kind of a skin as that of a sheep which is raised in the United States. In general, it may be said that skins from animals inhabiting warm countries are more likely to be serviceable than those from the same kind of animals inhabiting cold countries. In the cold countries more of the strength goes into the fur or hair which protects it, while in warm countries a greater amount of strength goes into the skin itself.
In addition to variations due to these causes there is likely to be a certain amount of variation in different parts of the same skin. That part of the skin which comes from the back of the animal is tougher than that which comes from the abdomen. The difference is very noticeable in the skins of some animals, less so in others.
Decay of Leather. Of late years there has been much dissatisfaction expressed over the decay of modern leathers. In many cases leathers 100 years old or more are in a fair state of preservation, while many leathers—perhaps we should say most leathers—30, 20 or even 10 years old, show signs of decay, and some have rotted away almost entirely. In no way is the decay of modern leathers shown more conclusively than in a long file of the sheep-bound set of the United States Public Documents. The earlier volumes, covering the 15th Congress up to the 36th, will in general be found to be in a good state of preservation. About the year 1860, however, marked deterioration appears. In some cases it seems as if the backs had entirely disintegrated. While a sheep-bound set is the best example of the decay of modern leathers, many libraries have been greatly annoyed by the decay of other leathers which are supposed to be much stronger than sheepskin.
So great was the dissatisfaction with modern leathers that in the year 1900 the Society of Arts in London appointed a committee to investigate modern leathers and to ascertain the best methods for preparing leathers for binding. The report of this committee was published in 1905, and a general knowledge of its contents is necessary for those who wish to know why leathers decay and how they may be preserved. Another valuable work which should be carefully studied is entitled "Leathers for libraries," published by the Sound Leather Committee of the Library Association in England. In a chapter of this book J. Gordon Parker, Ph. D., Director of the London Leather Industries Research Laboratories, tells us that the chief causes of decay are as follows:
1. The introduction of tanning materials other than oak and sumac, stronger in tannin, and more rapid in their action. Many of these tanning materials are unstable, and the leather produced disintegrates on exposure to light and air.
Tanning is the process of changing hides, which are animal matter subject to decay, into material which is strong and flexible and which is not subject to decay. There are two groups of tanning materials. The one called the pyrogallol group, which includes sumac, gall nuts and oak bark, is commended by the Committee of the Society of Arts. The other is called the catechol group and is strongly condemned. Among the materials belonging to the catechol group are hemlock bark and larch, used chiefly in this country, and turwar bark used largely in tanning East Indian goat and sheep skins.
The United States Government Printing Office proposals call for leathers tanned with a pyrogallol tannin, since it has been proved that such leathers prove most resistant to the evil effects of light, heat and gas. If a skin has been tanned with sumac, or sumac in combination with oak bark, it has received the best possible preparation for its life as a bookbinding leather.
It is not possible, neither is it necessary, to have all leathers tanned with sumac. Those leathers which are intended to remain on the shelves for many decades, should be in this tannage. Those which will be discarded in a few years may be tanned in a less expensive manner. Even some of the quick, modern materials, which accomplish in a few hours what once would have taken weeks, are not too poor for leathers which are not to be kept indefinitely.
Even the expert cannot detect skins which have not been tanned and dyed properly, but leathers which last a short time may be suspected either of being improperly tanned or of having some kind of injurious acid in their composition.
2. The use of dried and cured skins of variable soundness imported from abroad. Goat, calf and sheep skins are imported into this country (England) from all over the world; some are simply dried in the sun, some salted, whilst others are cured with various ingredients.
3. The use of infusions of acids and other bleaching agents to produce bright and even shades of colour.
Skins tanned with sumac are light-colored and can be dyed any desired color. Most other tanning materials, however, make darker-colored skins, which can be dyed only with dark colors. It has been found possible to scour and bleach skins with sulphuric acid and to re-tan with sumac.
4. The use of sulphuric or other mineral acids for the purpose of developing the depth of colour during the process of dyeing.
Sulphuric acid is the cause of decay of over 90% of modern bookbinding leathers. Having once been used, it cannot be wholly removed without the use of other chemicals.
5. The shaving and splitting of skins for producing an even substance.
In splitting and shaving, the long, strongest fibres of the skin are torn or cut off, and the part which remains for binding purposes is the weakest part of the skin.
6. Printing and embossing grains upon leather, together with other methods of finishing now in common use.
There are various ways of bringing out the natural grain of leathers which are perfectly legitimate and which do no harm. The danger in graining comes when the grain is embossed by means of a plate, which is heated and pressed on the skin. No good leather should ever be embossed.
7. The stripping, scouring, souring and re-tanning of East India leathers (Persians).
Some imported skins are only partially tanned, and it is necessary to wash out the tannin with some kind of alkali, which also takes out much of the natural grease of the skin. They are then treated with sulphuric acid and re-tanned. They are always poor and are seldom sold as re-tanned skins.
8. The removal of the natural grease or nourishment of the skin.
The foregoing eight causes of decay are beyond our direct control. The leathers are manufactured and put on the market, and the binder has to use such as he is able to obtain. No matter how much the librarian may insist upon leathers free-from-acid, he is helpless if the binder cannot obtain them. All that he can do is to insist that leathers without acid must be used, if obtainable.
Although these causes of decay are beyond the librarian's control, there are several causes of decay quite within his power to avoid. They are the following, due to improper methods used in binding, or to physical conditions after the book is on the shelf:
1. Direct sunlight.
2. Gas fumes. This evil is hard to guard against if there are gas pipes in the building. There is sure to be more or less leakage, and even a small amount of gas in the air has a bad effect upon leather.
3. Tobacco smoke. This is not likely to be very detrimental in libraries, since the rules generally forbid smoking.
4. Excessive dampness, which encourages mildew.
5. Extreme dry heat. A temperature much in excess of 70° Fahrenheit is likely to dry up the oil which gives flexibility to leather.
6. Undue wetting or stretching the leather in covering. Some binders soak the leathers and stretch them in placing them on the books. When the leathers dry they shrink, the fibres are strained and the life of the leather shortened.
7. Use of poor paste in binding. This frequently sets up a fermentation that is very harmful to leathers.
8. Dust, especially in conjunction with dampness, is very injurious to leather.
Doubtless there are other things which have a deleterious effect upon leathers in libraries; but if a library is well ventilated, if leather-covered books are not kept in cellars or basements that are very damp, or where direct sunlight can fall upon them, and if the binder uses good paste and proper care in covering the books, we may reasonably place the responsibility of undue decay of leathers upon the manufacturers.
The various reports quoted so far have dealt with qualities of leathers due to tanning, manufacture, method of binding and time in use. Natural or mechanical qualities of leathers have not been touched upon. Those who are interested in this phase of the question should read the report of Mr. Cedric Chivers on "The relative value of leathers and other binding materials," made at the meeting of the American Library Association at Pasadena in 1911. Mr. Chivers employed Mr. Alfred Seymour Jones, in England, to make tests which would show the tearing and breaking strain of various leathers. These natural qualities of leathers are obviously important, but too much stress must not be laid upon them. It is possible that a leather naturally strong and tough when new would rapidly deteriorate with age. The records as presented in Mr. Chivers' report must be taken in conjunction with facts determined by the investigation of the Society of Arts. In the main, however, it will be found that leathers which best stood the tests of the Society of Arts also showed the greatest resistance to the tearing and breaking strains made by Mr. Chivers.
Preservation of Leather. Various attempts have been made both by librarians and others to discover some substance which would preserve leather effectually after the book is bound. Some of these attempts have been temporarily successful, but time alone will tell whether leathers are permanently preserved by the treatments used, or whether applications of the preservative must be frequently made. Owing to the fact that in law libraries practically all the books published previous to 1900 were bound in sheepskin, the lasting qualities of leathers is a question that affects law libraries more than any other. Dr. Wire, of the Worcester (Mass.) County Law Library, who has made a careful study of the problem, advises the use of vaseline or some other similar by-product of petroleum well rubbed into the leather with the bare hand and allowed to dry in the air until the leather has absorbed it. Better results were obtained by allowing the volumes to dry in the summer by natural heat instead of artificial heat in the winter. For some books Dr. Wire makes use of a bookbinder's varnish after the softening product has thoroughly penetrated the leather. A full description of the processes may be obtained from Dr. Wire's pamphlet, "Leather preservation," published in 1911.
Some of the disadvantages of Dr. Wire's method are:
1. The necessity of rubbing in the preservative from three to five times, according to the condition of the leather at the time of first treatment.
2. The care necessary to prevent the material used from smearing tables, trucks, floor, shelves and clothing at time of application; also when books are back on the shelves the care required to keep from rubbing against them and the necessity of wiping them off when they are handed to readers.
3. The tendency of books to swell at the back when first treated in this way, demanding extra care lest, in an effort to pull out one book, a whole shelf-full fall to the floor.
4. The repetition of the process after ten years.
It is possible that these drawbacks will be sufficient to dissuade all except the most stout-hearted from using this method of preserving leather. Rebinding in cloth seems to be much more simple and, on the whole, not much more expensive.
The question of a preservative is discussed in the Report of the Society of Arts, from which the following quotation is taken:
Enquiries have frequently been made as to the use of preservative pastes upon old bindings. It has been mentioned that the seasonings of white of egg or blood albumen usually employed in finishing leather have some preservative effect, and no harm can arise from the application of very thin coatings of white of egg. The use of ammonia to thin or preserve the solution must be avoided, but the whites, after thorough beating, may be rendered antiseptic by the addition of a small quantity of camphor, thymol, or some essential oil. Vaseline has been employed as a dressing, and, if otherwise suitable, will no doubt have a preservative effect upon the leather. A very moderate use of the wax, soap, and turpentine preparations made as shoe pastes, is also likely to be beneficial, and no doubt a special preparation might be made on these lines which would be still more suitable. Paraffin wax dissolved in benzine is also harmless, and the surface to which it has been applied takes a good polish with a flannel after drying. Professor Proctor has experimented with a finish introduced by the Berlin Aniline Company some years ago for coloured leathers, with apparently satisfactory results. The preparation is practically a very hard stearine soap with excess of stearic acid, and is made by boiling 8 parts of stearic acid with 1 part of caustic soda and 50 parts of water until thoroughly dissolved, and then adding 150 parts of cold water and stirring till the material sets to a jelly. It is applied very thinly with a sponge or rag, and after thorough drying is polished with a soft brush or flannel. The alkali present in the soap is useful in neutralising any mineral acids contained in the leather. In very acid leathers it has been noticed that the sodium sulphate so formed will sometimes appear upon the surface as a white film, but this is easily removed with a damp cloth, and the surface, after drying, repolished with flannel.
Old books which it is desirable to preserve as long as possible in their original bindings and books which will be used very little may be treated with some form of preservative. If the book is to be much used, it would better be rebound. Dr. Wire's experiments have been carried on exclusively with law books. Whether the same processes could be used on books bound in morocco or pigskin is something that has not yet been determined. Most leather-bound books break first at the joint. The sheep bindings in a law library would show signs of disintegration long before the leather reached the breaking point, whereas the librarian would first notice that morocco was decaying when the leather actually cracked. Once cracked, no amount of preservative would do any good.
KINDS OF LEATHER[3]
The leathers that have been used in binding books have come from all sorts of animals, but so far as the librarian is concerned the skins of four animals only need be taken into consideration—the sheep, the cow, the pig and the goat. In England some experiments have been made with sealskin, but it has not been used long enough to give any definite idea of its resistance to the encroachments of time.
[3] The prices of leathers given in the text are those which prevailed during the summer of 1915.
Sheepskin
Sheepskin is a soft, flexible leather with weak fibres, and with a surface easily abraded. It has been used for bindings practically ever since books were put into leathers; and, under the old methods of tanning and manufacturing, proved satisfactory. In many libraries it is possible to see leather books bound in sheep in the 17th century which are in a good state of preservation. Even the sheep of the beginning of the 19th century is frequently well preserved. Since 1860, however, the quality of sheep has greatly deteriorated. This is bad enough, but unfortunately sheep likes to masquerade under the name of morocco and other leathers of a better grade, so that its use is much more extensive than appears at first sight. In the process of imitation the grain of the leather imitated is stamped on the skin. When this is done it generally takes an expert to detect the fact that the leather is not what it pretends to be, and even experts are sometimes deceived after the leather is on a book.
The strongest sheepskins are made when tanned with oak bark. Sumac, which is such a valuable tanning material with other leathers, is here inferior to oak.
There are two kinds of sheepskin, the wool sheep which is known to all, and the hair sheep which is not found in the United States, and which in reality is a cross between a sheep and a goat. The hair sheep comes from India, China, South America and Africa, generally from mountainous districts. It has a much tougher fibre and is a better wearing skin than that of the wool sheep. Unfortunately most of these skins, which are all imported, are made into shoe leather. When properly tanned they are very suitable for library binding, and their use for that purpose is increasing.
The wool sheepskin in its natural color has been used for many years for binding law books. It is seldom used for anything except government documents and law books, and for this reason is known as "law-sheep."
Roan. Roans, the term used for sheepskins after they are dyed, can be used advantageously on books which will be handled a great deal, and which in any event will not stay on the shelves indefinitely. Properly tanned and dyed, they make a satisfactory leather for a time, but their life under the best of conditions seldom exceeds ten or twelve years. While this is true of good roans, it unfortunately remains true that in the United States, at least, it is difficult to get roans that are properly tanned and dyed. Therefore, unless one is sure that the quality of the skin is the best, he should use no sheep under any conditions.
Skiver. Skiver is the outside of a sheepskin which has been split, the inner side being known as the flesher. It is a leather much used for commercial binding, but since the splitting process takes away a great part of the strength of the skin, leaving it not much stronger than strong paper, skiver is wholly unfitted for library use.
Cowhide
Cowhide, sometimes known as American russia, is a leather which has increased enormously in use in the last twenty-five years. It is a thick, coarse leather, rather unattractive in appearance, strong when new, but with age rapidly deteriorating in quality, even when no deleterious substance has been used in tanning or dyeing. It is a harder leather to work than roan, but the quality is much more uniform and it can be used advantageously for binding fiction and other books which will be much used. In its natural state (undyed) it can be used in place of law-sheep for law books, but has a tendency to become dark. It can be obtained in many colors. Since it is too thick a leather to be used in full thickness, practically all skins are split, and the amount of flesh left with the grain determines the weight of the leather. A greater or less amount is taken off according to the purpose for which the leather is intended. Bookbinding cowhide costing 20c to 25c. a square foot is the lightest weight leather that has the right to be called cow.[4] The life of cowhide is from five to twelve years.
Buffing. Buffing is practically only the grain of cowskin from which almost all the flesh has been split. It is not suitable for library books, since it is very thin and begins to disintegrate in less than five years. After it is on the volume it is hard to detect, so that some library binders have been tempted to use it instead of cow. But as buffing is never sold as cow, the library binder has no excuse for keeping it in stock.
[4] This is the normal price of cow. The European war has had the disastrous effect of raising the price and lowering the quality. Until conditions become normal again all cowhide should be shunned.
Pigskin is one of the strongest leathers, having a hard, resisting surface and a good, tough fibre. In the grain, the holes which were left when bristles were removed are plainly visible, giving the leather a distinctive appearance, which can be imitated successfully, but which is much less often imitated than the grain of morocco. If there be doubt of the genuineness of pig, soak a piece of the leather until it has absorbed a quantity of water, and then stretch it. If the grain pulls out, it is imitation; if genuine, the bristle holes still show plainly. Oak bark tanning is the best for this leather, and, since it is more nearly gristle (less fibrous) than other leathers, dyes and chemicals should not be used which will interfere with its quality of resisting friction. It should be used in its natural color whenever possible.
Pigskin frequently comes in skins which are too thick for the binder to work easily, or which are very uneven in thickness. In such cases the paring down of the skin is likely to injure its strength. Because of its thickness pig is generally supposed to be more suitable for large than for small books, but inasmuch as several binders have used it successfully for years on small books, it may be taken for granted that it can be used with good results on all books, large or small, which are to receive hard usage. It needs constant handling, and the absorption of a certain amount of oil from the hands to keep it pliable. Otherwise it dries rapidly and cracks along the joint. This, however, is true of all leathers to a greater or less extent. Pig costs from 40c. to 45c. a square foot.
Goat
The leather which makes the strongest and most attractive binding comes from the skins of goats and is called morocco, because it originally came from that country. In the course of time goat skins from other countries were tanned with sumac (originally a distinguishing characteristic of a genuine morocco), but the same name was applied so that we now have the paradoxical terms, Turkey morocco, Levant morocco, etc. Moroccos have a beautiful grain, are flexible, soft and pliable to the hand, and resist hard wear; qualities which contribute to their great popularity.
Morocco varies greatly in quality as well as in appearance. Unfortunately the skins which are best in quality, considering the length of time they will wear, are not always those best in appearance. The skins of goats with long hair from the colder countries make beautiful bindings; but the skins of goats from the hot countries, such as the interior of Africa, having short hair, while not so attractive in appearance, are tougher and wear longer. In addition to the many grades of genuine morocco there are as many more imitations of it made from sheepskin, cowhide, etc. Only the expert can detect some of them in the skin, and even he may be deceived when the leather is on the back of the book.
In general it should be said that genuine morocco is the most expensive leather that a library can use, and that it can be used to the greatest advantage only occasionally. It makes an excellent binding for large reference books which are constantly handled, for art books which must be attractively bound, and for some periodicals which are much used in reference work. It is not used nearly so much in libraries to-day as it was ten or fifteen years ago, and it is quite safe to say that it will be used less ten years from to-day than it is now.
Levant morocco, made from the skins of Angora goats, is the most expensive and most beautiful leather used in binding. It has a large, prominent grain, but is far too expensive for any library to use, especially when it must be conceded that in its wearing quality it does not equal that of some less expensive moroccos. Mr. Chivers' test showed that so far as tensile strength goes, this leather is very much weaker than many leathers much less expensive. When the skin has been subjected to pressure until the surface is smooth it is known as "crushed levant."
Turkey morocco, made of skins of goats from Turkey, is a very strong, durable leather which all libraries will find occasion to use from time to time. It is very easily imitated. Under exposure to atmospheric conditions existing in many libraries its life may not extend beyond thirty years. In one library at least, where conditions of light and heat were poor, the best Turkey morocco that the market afforded showed signs of disintegration within twelve years. Good Turkey morocco can be obtained for 35c. a square foot.
Persian morocco, which comes from the skin of a Persian sheep (not goat), is not particularly attractive in appearance and is very poor in quality. It is used extensively for commercial work, but is absolutely valueless for library binding.
Niger morocco is a goat skin which comes from the interior of Africa, generally by way of Tripoli, and is by no means a recent discovery, though we knew little about it five years ago. It is tanned by natives according to some method of vegetable tanning not completely known at this time. While in appearance it is not so attractive as some other moroccos, because of blemishes due to carelessness in handling and to the imperfect removal of some of the hairs, it has been proved by the tests made under the direction of Mr. Chivers to be stronger than all other moroccos; the inference is that it is more durable. Until recently it has been very hard to obtain in the United States.
Bock morocco is not a morocco but a split Persian sheep so poor in quality that it is mentioned only to be condemned.
Calfskin
Calfskin in all its various characters, such as divinity, kip, marbled, mottled, smooth, tree, or just plain calf is a very beautiful leather much used in the past for binding books for individuals. For this purpose it has, of late years, been crowded out by Levant morocco. It has a soft, smooth surface which disintegrates rapidly under the action of heat and gas and has little strength even for temporary use. For the library it is useless.
Russia Leather
This is a brownish-red leather made from the skins of different animals, tanned with willow bark and filled with a preparation of birch oil which gives it its peculiar odor. Neither in its genuine form nor in imitation is it a useful leather for libraries.
Sealskin
Although experiments have been made with it in some English libraries sealskin has never been much used in the United States for library binding. It is made from the skins of the hair seal, the supply coming from all parts of the North Atlantic Ocean. According to Mr. Douglas Cockerell and other binding experts in England, the skin is peculiarly suited for library use. It is reported to be a hard-wearing leather, tough and pliable, even in quality so that no part of the skin must be discarded because too thin or too weak, and possessing a beautiful grain. The price ranges from a point somewhat higher than that of the poorer moroccos to one somewhat lower than the higher prices. Unfortunately it can be easily imitated.
Vellum
Probably no discussion of leather is complete without mentioning vellum, a binding material which does not resemble leather, but which nevertheless is made from calfskin or sometimes from goat skin. It is prepared by the use of lime, and as far as the actual wear on flat surface is concerned, is perhaps better than any leather. It is, however, very susceptible to moisture, which makes it warp; and to light, which makes it hard and brittle. Since it is very hard, does not bend easily and is hard to work, its chief use is on the corners of books to protect them and make them less likely to break or rub. Large libraries have used it somewhat for this purpose, but the use is dying out.
In making a study of leathers it is well to obtain samples of all kinds, including those which are unsuitable for library use, and to examine them carefully, noting the appearance of the grain, thickness of skin, flexibility, and softness of surface. Perhaps more money can be wasted through ignorance of the comparative values of different kinds of leather which it is permissible to use in library binding, than in mismanagement of any other part of binding.