Leather
LEATHER
Of all the materials used by the bookbinders, leather is the most
important and the most difficult to select wisely. It is extremely
difficult to judge a leather by its appearance.
"We find now, that instead of leather made from sheep, calf, goat, and
pigskins, each having, when finished, its own characteristic surface,
that sheepskins are got up to look like calf, morocco, or pigskin;
that calf is grained to resemble morocco, or so polished and flattened
as to have but little character left; while goatskins are grained in
any number of ways, and pigskin is often grained like levant morocco.
So clever are some of these imitations, that it takes a skilled expert
to identify a leather when it is on a book."
There have been complaints for a long time of the want of durability
of modern bookbinding leather, but there has not been until lately any
systematic investigation into the causes of its premature decay.
By permission, I shall quote largely from the report of the committee
appointed by the Society of Arts to inquire into the subject. There
are on this special committee leather manufacturers, bookbinders,
librarians, and owners of libraries. The report issued is the result
of an immense amount of work done. Many libraries were visited, and
hundreds of experiments and tests were carried out by the
sub-committees. There is much useful information in the report that
all bookbinders and librarians should read. The work of the committee
is not yet finished, but its findings may be accepted as conclusive as
far as they go.
The committee first set themselves to ascertain if the complaints of
the premature decay of modern bookbinding leather are justified by
facts, and on this point report that:--
"As regards the common belief that modern binding leather does decay
prematurely, the sub-committee satisfied themselves that books bound
during the last eighty or hundred years showed far greater evidence of
deterioration than those of an earlier date. Many recent bindings
showed evidence of decay after so short a period as ten, or even five
years. The sub-committee came to the conclusion that there is ample
justification for the general complaint that modern leather is not so
durable as that formerly used. To fix the date of the commencement of
this deterioration was a difficult matter; but they came to the
conclusion that while leather of all periods showed some signs of
decay, the deterioration becomes more general on books bound after
1830, while some leathers seem to be generally good until about 1860,
after which date nearly all leathers seem to get worse. The
deterioration of calf bindings at the latter end of the 19th century
may be attributed as much to the excessive thinness as to the poor
quality of the material."
The committee endeavoured to ascertain the relative durability of the
leathers used for bookbinding, and after visiting many libraries, and
comparing bindings, they report as follows:--
"As to the suitability of various leathers, the sub-committee came to
the conclusion that of the old leathers (15th and 16th century), white
pigskin, probably alum 'tanned,' is the most durable, but its
excessive hardness and want of flexibility renders this leather
unsuitable for most modern work. Old brown calf has lasted fairly
well, but loses its flexibility, and becomes stiff and brittle when
exposed to light and air. Some of the white tawed skins of the 15th
and 16th century, other than white pigskin, and probably deerskin,
have lasted very well. Some 15th and 16th century sheepskin bindings
have remained soft and flexible, but the surface is soft, and usually
much damaged by friction. Vellum seems to have lasted fairly well, but
is easily influenced by atmospheric changes, and is much affected by
light. Early specimens of red morocco from the 16th to the end of the
18th century were found in good condition, and of all the leathers
noticed, this seems to be the least affected by the various conditions
to which it had been subjected. In the opinion of the committee, most
of this leather has been tanned with sumach or some closely allied
tanning material. Morocco bindings earlier than 1860 were generally
found to be in fairly good condition, but morocco after that date
seems to be much less reliable, and in many cases has become utterly
rotten. During the latter part of the 18th century it became customary
to pare down calf until it was as thin as paper. Since about 1830
hardly any really sound calf seems to have been used, as, whether
thick or thin, it appears generally to have perished. Sheepskin
bindings of the early part of the century are many of them still in
good condition. Since about 1860 sheepskin as sheepskin is hardly to
be found. Sheepskins are grained in imitation of other leathers, and
these imitation-grained leathers are generally found to be in a worse
condition than any of the other bindings, except, perhaps, some of the
very thin calfskin. Undyed modern pigskin seems to last well, but some
coloured pigskin bindings had entirely perished. Modern leathers dyed
with the aid of sulphuric acid are all to be condemned. In nearly
every case Russia leather was found to have become rotten, at least in
bindings of the last fifty years."
On the question of the causes of the decay noticed and the best
methods of preparing leather in the future, I may quote the
following:--
"The work of a sub-committee, which was composed of chemists specially
conversant with the treatment of leather, was directed specially to
the elucidation of the following points: an investigation of the
nature of the decay of leather used for bookbinding; an examination of
the causes which produced this decay; a research into the best
methods of preparing leather for bookbinding; and a consideration of
the points required to be dealt with in the preservation of books.
"Taking these points in order, the first one dealt with is the
question of the nature of the decay of leather. To arrive at their
conclusions on this subject, the sub-committee made a number of tests
and analyses of samples of decayed leather bookbindings, as well as of
leathers used for binding. The committee found that the most prevalent
decay was what they term a red decay, and this they think may be
differentiated into old and new, the old red decay being noticeable up
to about 1830, and the new decay since that date. In the old decay,
the leather becomes hard and brittle, the surface not being easily
abraded by friction. The older form is specially noticeable in
calf-bound books, tanned presumably with oak bark. The new form
affects nearly all leathers, and in extreme cases seems absolutely to
destroy the fibres. Another form of deterioration, more noticeable in
the newer books, renders the grain of the leather liable to peel off
when exposed to the slightest friction. This is the most common form
of decay noted in the more recent leathers. In nearly all samples of
Russia leather a very violent form of red decay was noticed. In many
cases the leather was found to be absolutely rotten in all parts
exposed to light and air, so that on the very slightest rubbing with a
blunt instrument the leather fell into fine dust....
"The second point is the cause of the decay. An extensive series of
experiments was carried out with a view of determining the causes of
the decay of bindings. The sub-committee find that this is caused by
both mechanical and by chemical influences. Of the latter, some are
due to mistakes of the leather manufacturer and the bookbinder, others
to the want of ventilation, and to improper heating and lighting of
libraries. In some cases inferior leathers are finished (by methods in
themselves injurious) so as to imitate the better class leathers, and
of course where these are used durability cannot be expected. But in
the main the injury for which the manufacturer and bookbinder are
responsible must be attributed rather to ignorance of the effect of
the means employed to give the leather the outward qualities required
for binding, than to the intentional production of an inferior
article.... Leathers produced by different tanning materials, although
they may be equally sound and durable mechanically, vary very much in
their resistance to other influences, such as light, heat, and gas
fumes.
"For bookbinding purposes, the sub-committee generally condemn the use
of tanning materials belonging to the catechol group, although the
leathers produced by the use of these materials are for many purposes
excellent, and indeed superior. The class of tanning materials which
produce the most suitable leather for this particular purpose belong
to the pyrogallol group, of which a well known and important example
is sumach. East Indian or 'Persian' tanned sheep and goat skins, which
are suitable for many purposes, and are now used largely for cheap
bookbinding purposes, are considered extremely bad. Books bound in
these materials have been found to show signs of decay in less than
twelve months, and the sub-committee are inclined to believe that no
book bound in these leathers, exposed on a shelf to sunlight or gas
fumes, can ever be expected to last more than five or six years.
Embossing leather under heavy pressure to imitate a grain has a very
injurious effect, while the shaving of thick skins greatly reduces the
strength of the leather by cutting away the tough fibres of the inner
part of the skin. The use of mineral acids in brightening the colour
of leather, and in the process of dyeing, has a serious effect in
lessening its resistance to decay. A good deal yet remains to be
learned about the relative permanency of the different dyes."
On analysis free sulphuric acid was found to be present in nearly all
bookbinding leather, and it is the opinion of the committee that even
a small quantity of this acid materially lessens the durability of the
leather.
"It has been shown by careful experiment, that even a minute quantity
of sulphuric acid used in the dye bath to liberate the colour is at
once absorbed by the leather, and that no amount of subsequent washing
will remove it. In a very large proportion of cases the decay of
modern sumach-tanned leather has been due to the sulphuric acid used
in the dye bath, and retained in the skin. We have examined very many
samples of leather manufactured and sold specially for bookbinding
purposes, from different factories, bought from different dealers, or
kindly supplied by bookbinders and by librarians, and have found them
to contain, in a large number of cases, free sulphuric acid, from 0.5
up to 1.6 per cent."
The publication of the report should tend to fix a standard for
bookbinding leather. Hitherto there has been no recognised standard.
Bookbinders have selected leather almost entirely by its appearance.
It has now been shown that appearance is no test of durability, and
the mechanical test of tearing the leather is insufficient. Sound
leather should tear with difficulty, and the torn edges should be
fringed with long, silky fibres, and any leather which tears very
easily, and shows short, curled-up fibres at the torn edges, should be
discarded. But though good bookbinding leather will tear with
difficulty, and show long fibres where torn, that is in itself not a
sufficient test; because it has been shown that the leather that is
mechanically the strongest, is not necessarily the most durable and
the best able to resist the adverse influences to which books are
subject in libraries.
The report shows that bookbinders and librarians are not, as a general
rule, qualified to select leather for bookbinding. In the old days,
when the manufacture of leather was comparatively simple, a bookbinder
might reasonably be expected to know enough of the processes employed
to be able to select his leather. But now so complicated is the
manufacture, and so many are the factors to be considered, that an
expert should be employed.
"The committee have satisfied themselves that it is possible to test
any leather in such a way as to guarantee its suitability for
bookbinding. They have not come to any decision as to the desirability
of establishing any formal or official standard, though they consider
that this is a point which well deserves future consideration."
It is to be hoped that some system of examining and hall-marking
leather by some recognised body, may be instituted. If librarians will
specify that the leather to be employed must be certified to be
manufactured according to the recommendations of the Society of Arts
Committee, there is no reason why leathers should not be obtained as
durable as any ever produced. This would necessitate the examining and
testing of batches of leather by experts. At present this can be done
more or less privately at various places, such as the Yorkshire
College, Leeds, or the Herolds' Institute, Bermondsey. In the near
future it is to be hoped that some recognised public body, such as one
of the great City Companies interested in leather, may be induced to
establish a standard, and to test such leathers as are submitted to
them, hall-marking those that come up to the standard. This would
enable bookbinders and librarians, in ordering leather, to be sure
that it had not been injured in its manufacture. The testing, if done
by batches, should not add greatly to the cost of the leather.
On the question of the qualities of an ideal bookbinding leather the
committee report:--
"It is the opinion of the committee, that the ideal bookbinding
leather must have, and retain, great flexibility.... (It) must have a
firm grain surface, not easily damaged by friction, and should not be
artificially grained.... The committee is of opinion that a pure
sumach tannage will answer all these conditions, and that leather can,
and will, be now produced that will prove to be as durable as any made
in the past."
The committee has so far only dealt with vegetable-tanned leather. I
have used, with some success, chrome-tanned calfskin. Chrome leather
is difficult to pare, and to work, as it does not become soft when
wet, like vegetable-tanned leather. It will stand any reasonable
degree of heat, and so might perhaps be useful for top-shelf bindings
and for shelf edging. It is extremely strong mechanically, but without
further tests I cannot positively recommend it except for trial.
While the strength and probable durability of leather can only be
judged by a trained leather chemist, there remains for the binders
selection, the kind of leather to use, and its colour.
Most of the leather prepared for bookbinding is too highly finished.
The finishing processes add a good deal to the cost of the leather,
and are apt to be injurious to it, and as much of the high finish is
lost in covering, it would be better for the bookbinder to get rougher
leather and finish it himself when it is on the book.
The leathers in common use for bookbinding are:--
Goatskin, known as morocco.
Calf, known as calf and russia.
Sheepskin, known as roan, basil, skiver, &c.
Pigskin, known as pigskin.
Sealskin, known as seal.
_Morocco_ is probably the best leather for extra binding if properly
prepared, but experiment has shown that the expensive Levant moroccos
are nearly always ruined in their manufacture. A great many samples of
the most expensive Levant morocco were tested, with the result that
they were all found to contain free sulphuric acid.
_Calf._--Modern vegetable-tanned calf has become a highly
unsatisfactory material, and until some radical changes are made in
the methods of manufacturing it, it should not be used for
bookbinding.
_Sheepskin._--A properly tanned sheepskin makes a very durable, though
rather soft and woolly, leather. Much of the bookbinding leather now
made from sheepskin is quite worthless. Bookbinders should refuse to
have anything to do with any leather that has been artificially
grained, as the process is apt to be highly injurious to the skin.
_Pigskin._--Pigskin is a thoroughly good leather naturally, and very
strong, especially the alumed skins; but many of the dyed pigskins are
found to be improperly tanned and dyed, and worthless for bookbinding.
_Sealskin_ is highly recommended by one eminent librarian, but I have
not yet had any experience of its use for bookbinding.
The leather that I have found most useful is the Niger goatskin,
brought from Africa by the Royal Niger Company; it is a very beautiful
colour and texture, and has stood all the tests tried, without serious
deterioration. The difficulty with this leather is that, being a
native production, it is somewhat carelessly prepared, and is much
spoiled by flaws and stains on the surface, and many skins are quite
worthless. It is to be hoped that before long some of the
manufacturers interested will produce skins as good in quality and
colour as the best Niger morocco, and with fewer flaws.
Much leather is ruined in order to obtain an absolutely even colour. A
slight unevenness of colours is very pleasing, and should rather be
encouraged than objected to. That the want of interest in absolutely
flat colours has been felt, is shown by the frequency with which the
binders get rid of flat, even colours by sprinkling and marbling.
On this point I may quote from the committee: "The sprinkling of
leather, either for the production of 'sprinkled' calf or 'tree' calf,
with ferrous sulphate (green vitriol) must be most strongly condemned,
as the iron combines with and destroys the tan in the leather, and
free sulphuric acid is liberated, which is still more destructive.
Iron acetate or lactate is somewhat less objectionable, but probably
the same effects may be obtained with aniline colours without risk to
the leather."