Obrázky stránek
PDF
ePub

with artificial materials, and a further test of breaking strain along the lines of A and B will demonstrate this. We have then a test with a piece cut as with C, with another as with B, and a third as A diagonally across the skin.

In Fig. X we have set out the result of testing a number of different kinds of skins. First the thickness in thousandths of an inch is given, then the tearing strain in pounds. The strength ratio is shown and the order of value of the skins compared with each other.

The first leather given, Niger leather unpared, with the total thickness of 190, suffers a tearing strain of 189 lbs., with a strength ratio of .99. If this be taken as a standard one may readily appreciate the values of leathers in respect to their tearing strains. It is a valuable coincidence that the best leather gives a tearing strain of one pound for a thousandth of an inch in thickness, as it facilitates comparisons. An examination of these figures will be instructive.

Our experiences are ratified with the skins of poor quality. Their lives being short, we had become cognizant of their failure, but our interest is aroused by the results given of the more costly and the leathers of greater repute. We were prepared from our practical experience to see that the calf leather should be demonstrated to be very weak, the strength ratio being .21, and the order of value to be 18 in the list given, but it must be viewed with some alarm to discover that French levant morocco should show a strength ratio of .40, and to offer for a thickness of 242 thousandths a tearing strain of only 97 lbs. This is against Niger morocco 190 thousandths to 189 lbs. It arouses the reflection that in the effort to obtain the colors and brightness required with modern bookbinding, much of the strength and nature of the morocco has been destroyed.

The leathers in the upper part of the table have been chosen with care, and the moroccos 7 and 5 and pigskins 6 and 12 have been prepared under the specification of the Society of Arts.

The leathers under the title of odd

pieces, were collected from a small bookbinder's shop where library books had not been bound. In other words, no effort had been made to obtain the best leather of the different sorts. The results are seen to be bad.

The deterioration of levant morocco is a matter to be viewed with alarm. The or der of value of one piece is 7, with a strength ratio of .63, while for another, the order of value is 16, and the strength ratio is only .29. These pieces of leather are similar in color, and were purchased from the same firm, but the poorer quality had been in house some fifteen years, showing a very serious deterioration.

The high value which is shown by the Niger leathers is not a little surprising when it is remembered that these leathers have been tanned by uncivilized natives. The figures have been submitted to Mr. Seymour Jones, who was a member of the committee appointed by the Society of Arts above mentioned, and the following valuable letter has been received, dealing with the subject from the point of view of an expert:

"The breaking strains, as given in yours of the 5th, go to confirm my work in the same direction, and all I have written or spoken on the subject. Two anomalies would appear to require explanation. Levant 87 M. thick breaks at 36 lbs. Again, a piece 55 M. breaks at 35 lbs. Both, I assume, are unpared. You will find that substance, as it increases, does not carry with it a corresponding increase in strength, that is, strength in proportion to substance increases at a decreasing ratio. This is due to the fact that as age creeps on the number of fibres do not increase, but do increase in thickness and some muscular strength, but later not proportionately. Examples: a rope made of 6 strands of 4" thick is not as strong as a rope made of 12 strands and 4" thick in diameter. The more fibres to a given area, so is the increase in strength proportionately. Hence if you have a piece of leather 2" square and 87 M. thick, and assume you have 1,000,000 fibres, it will not have a breaking strain equal to a 2" say 45 M.

thick and containing 1,500,000 fibres. The second anomaly, namely, why does levant pared to 47 M. break at 22, and Niger pared to 32 M. break at 33? The explanation rests entirely upon two factors:

1. Levant contains from 40 to 50 per cent of tan, which implies over-tanning, whereas Niger contains about 27 per cent of tan.

2. The levant has been robbed of its natural nourishing fat prior to tan. The small amount of fat in Niger has been left in. If the levant contains grease, and still has a lower tearing factor, it follows that the displaced natural fats have not been properly replaced to insure absorption by the fibres as in life. The Nigerian tanner in his so-called ignorance, has been working along the lines of least resistance, allowing atmospheric conditions, temperature and time to operate, with results which give a higher satisfactory result than can be obtained under civilized conditions. In fact, we have much to relearn, but unfortunately the civilized tanner thinks he knows better. I do not know of any skin on the market at the present time which possesses the qualities appertaining to longevity, withstanding attrition, etc., as is pos

sessed by those tanned in Nigeria, and now known as Niger skins. I am of the opinion that of the bookbinding skins on sale, the Niger skins are the most suitable and meet all the demands made by the Society of Arts report. Upon that point I have no hesitation in expressing that opinion."

It must be borne in mind that the figures here given deal with only one quality of the leathers under consideration, that is, their strength in resisting the tearing strain. Other important qualities are necessary. This may be illustrated by refer ring to the hand-grained Persian goat, whose order of value is 10, and whose strength ratio is .52 in tearing strain. This leather has been subjected to the following criticism by the Society of Arts Committee, and we may therefore expect to discover very different results after two or three years' use in the library. The report says: "The Persian tanned goat skins are extremely bad. Books bound in this material are shown to have become unfit for

use in less than twelve months after binding." This doubtless because of bad tanning, the results of which are not immedi. ately apparent.

The breaking strain of various leathers is arrived at by taking strips in the way depicted in Fig. IX, A and B. These will be found set out on Fig. XI, first the thickness, then the breaking strain, the strength ratio follows and its order of value.

In a general manner the tests for breaking coincide with the "tearing" tests, and become together valuable as giving data of the comparative mechanical strength of leathers. It is necessary always that this strength should be allied with good tan ning and dyeing, in order to obtain the full advantages required.

This short inquiry has already shown the necessity for constant watchfulness in the selection of leathers for books requiring to be protected either for extra hard usage or for a very long life.

Until these tests were undertaken we have always assumed that the higher priced French levant moroccos were above any reproach, except that of their cost, but it is here demonstrated that they are not reliable, and that the native tanned skins of Africa are greatly their superior in both respects of strength and probable longevity.

Are we therefore to select from the open market Niger leather when it is required for either of these two purposes-of strength and longevity-for the binding of books?

The following experiment will show the danger of trusting with any confidence to the commercial use of the word "Niger." Leathers purporting to be Niger leather and to have the wearing qualities which have already become known in the trade, were recently offered for sale and were subjected to chemical and mechanial tests. The results showed that in one case the leather was decidedly not Nigerian, and in the other that if it were Nigerian it had been so abused in its tanning and dyeing treatment as to destroy its distinguishing merits.

The mechanical tests show the results

depicted upon Fig. XII. While real Nigerian leather shows a tearing strain of 189 to a thickness of 190, the leather offered as Nigerian leather and now under question showed for a thickness of 88 a tearing strain of only 27. In other words, real Nigerian leather showed three times the strength of the imitation.

This demonstrates either one of two cases: the leather, which we will call "Imitation," could not have been Nigerian leather at all, or it had become partially destroyed in fitting it for the market. The grain was evidently plated, the color far too even and the skin too perfect in appearance to be real Nigerian leather. A breakdown in use would occur indubitably where strength would be required, and should the leather be used for books requiring to give long service, its treachery would become presently more apparent and disastrous. If the leather were real Nigerian and had been dealt with so that twothirds of its original strength would be lost, other results of premature decay would most certainly follow. It is, therefore, apparent that care and inquiry must be made by librarians who intend to have their books properly bound and covered.

The importance of using the best of leathers for the binding of books cannot be overestimated. These are not necessarily high in price if fine finish is dispensed with.

There is no material existing which can be compared with leather for lining or binding the backs of books.

It is the only thing we know of which, with its many qualities of thickness, pliability, strength and tenacious adhesiveness, is at all adapted to the varying qualities of modern books.

Fig. I shows how many varieties there are, and a calculation from these data or the experience of any librarian or bookbinder will tell of many hundreds of kinds of books.

The range of appropriate materials when leather is not used is woefully short, and in no case can any of them be used for the linings of the backs of books; their effectiveness is limited to their service as covering materials only. Leather answers

both purposes of covering and lining or binding the back.

The statement in Fig. XIII will illustrate this point. While the books themselves have a very wide range of inconstancy, the materials at the disposal of the machine binder, as distinguished from the leather binder are, as seen, very limited.

In cloth, endpapers, linings, etc., as here set out, the qualities are very few. The case is totally different with leather. A careful and informed binder is able to obtain such a range of qualities in leather as enable him appropriately and effectively to deal with the hundreds and more variations of modern books.

Much has recently been written of machine sewing and its value for library books, but machine sewing can be used only by sewing through the fold, and it has been demonstrated that with 7,000 different books published during the last three years, only 400 of them were of good enough quality to allow of being sewed through.

All the other 6,600 books were of paper so bad that the act of folding deprived the paper of 50 per cent of its strength, while its original strength showed a deterioration of more than 50 per cent over that in common use twenty years ago.

Nearly all modern books must be handsewed in order to give reasonable service, and they must be bound and covered with pliable, tough and chemically pure leather to insure long life.

The librarian who is interested enough to give the subject a little time and attention, may obtain both these qualities for the books under his charge, and this at no greater cost than is often incurred for unreliable work and materials.

Mr. HILL: Mr. Chivers showed us a piece of levant morocco, a piece which had been in use fifteen years, and I wonder if he has a piece of pig skin for comparison in the same way.

Mr. CHIVERS: No, I have not, but I can tell you about the pig skin. I was chiefly instrumental, twenty-five years ago, in bringing pig skin on the market. Pig skin is only the grandson of hog skin. I never

[graphic][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][graphic]
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
« PředchozíPokračovat »