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 bas.e.m.e.nts 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 a.s.sociation 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 (Ma.s.s.) 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 repet.i.tion 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 alb.u.men 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 quant.i.ty 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.

Footnote 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 doc.u.ments 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, coa.r.s.e 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.

Footnote 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