CHAPTER II.
Why do modern leather bindings decay? Is it
possible to obtain a leather for bookbinding purposes
as good and as durable as the leather produced
from the 16th to 18th century? These are the two
problems which the Committee on Bookbinding Leather
appointed by the Society of Arts set themselves to investigate.
Fortunately we are able to solve both problems.
In the olden days all skins were tanned with a liquor
made from either oak bark or sumach, and in some cases
a mixture of the two. The skins used by the tanner were
usually obtained direct from the butchers. After soaking
and cleansing they were then limed for a period sufficiently
long to loosen the hair. After the removal of the hair
and superfluous flesh and fat, the skins were washed in
several changes of fresh soft water to remove the excess of
lime, the process being assisted by working the skins over
on a beam with a blunt knife. When in suitable condition
they were brought into sour, old tan liquors. There was
no hurry, the skins being slowly tanned in weak infusions,
and when the process was complete, the leather was simply
washed free from superfluous tan, dyed with wood or
other vegetable dyes, rinsed free from excess of dye-stuff,
and dried out. The leather was afterwards softened
by stretching, and polished or glazed by brushing the
skin over with oil, soap, beeswax, or a solution of
some moss. Such leather lacked the high finish, the
regular colour, the bright shades of modern leather, but
it lasted fifty or one hundred years with hard wear,
and, under favourable conditions, appears to be almost
imperishable.
The finish, or general appearance, of leather continued
to improve up to about 1850, but after that date some of
the bindings examined showed signs of rapid deterioration
in quality. This deterioration increased on bindings
subsequent to 1870, and probably 75 per cent. of the
leather used for bookbinding during the last twenty
years either has already decayed or will do so within a
comparatively short time.
Now to deal with the answer to the first question,
Why do modern leather bindings decay? The chief
causes are as follows:—
1. The introduction of tanning materials other than
oak and sumach, stronger in tanning, and more
rapid in their action. Many of these tanning
materials are unstable, and the leather produced
disintegrates on exposure to light and air.
2. The use of dried and cured skins of variable soundness
imported from abroad. Goat, calf, and
sheep skins are imported into this country 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.
4. The use of sulphuric or other mineral acids for the
purpose of developing the depth of colour during
the process of dyeing.
5. The shaving and splitting of skin for producing an
even substance.
6. Printing and embossing grains upon leather,
together with other methods of finishing now in
common use.
7. The stripping, scouring, souring, and re-tanning of
East India leathers (Persians).
8. The removal of the natural grease or nourishment
of the skin.
These eight causes, although by no means exhaustive,
are, however, the chief factors in the deterioration of
modern leather; and in as few words as possible I will
explain the reason of their introduction and effect.
As the industry advanced there were found in different
parts of the world tanning materials other than oak and
sumach, some of which were two, three, or five times as
rich in tannin as oak, thus making infusions of greater
strength, and consequently of quicker action, with the
result that leather which formerly required from three to
six months to tan was turned out in almost as many days,
or, at the most, in as many weeks. It was not realised,
however, that these different tanning materials contained
tannins of different qualities, capable of producing quite
a different leather to that produced by means of oak or
sumach. The experts who spent months testing and
investigating this question came to the unanimous conclusion
that the speed of tannage or the strength of the
tanning liquor had very little to do with the wearing
qualities of the leather produced, but found that some
of these new materials contained tannins of a different
chemical nature from that of sumach, and that they
produced leather of an unstable character, some of the
leathers undergoing change in a few hours on exposure
to strong light and air. On the other hand, some of
the new tanning materials produced permanent leathers
practically equal to sumach. Those tanning materials,
therefore, which contained tannins of the catechol series,
including the tannins of hemlock, larch, quebracho,
mangrove, gambier, and turwar, were condemned, as all
these materials produce a leather which on exposure
to light and air turns first a red shade of colour and afterwards
develops what is now well known by bookbinders
and librarians as the red decay, where the leather crumbles
off on application of friction. On the other hand, tanning
materials of the pyrogallol class, such as sumach, galls,
divi-divi, myrobalans, oak, and chesnut, produce a leather
which is practically unaffected by light or air. Further,
it was found in every case where authentic bindings dating
from the 13th century onwards were examined the tanning
material used was one of this pyrogallol series. On the
other hand, leathers which showed the red decay were
in every case found either to have been tanned with
tanning materials of the catechol series, or were rotted
with acid.
The second cause of trouble is the manufacture of
leather from skins from distant lands which have been
improperly or insufficiently preserved for export. It
often happens that the fibres have partly perished before
the tanner receives the skins, the resulting leather is
therefore poor, spongy, and partially perished, making
thin leather, which sometimes, on account of its thinness,
will cut up apparently economically for the binder,
but not economically for the librarian or the owner of
books, as the leather cannot possibly be as good or have
as long life as leather manufactured from a sound skin.
Bright even shades and light fancy colours previous
to the introduction of acid bleaches were manufactured
from sumach-tanned skins only, sumach alone producing
a leather of a light cream colour, and therefore capable
of taking practically any shade of dye. Most other
tanning materials produced dark foundations, on which
it was practically impossible to dye any but a dark shade.
Gradually, however, manufacturers found leather tanned
with materials cheaper than sumach could be scoured
and bleached with acids, then re-tanned with sumach,
thus producing a light, even-coloured leather, which with
the dye produced light shades. The cheapest, and at the
same time the most effective, acid for this purpose was
vitriol or sulphuric acid. This, in common with other
mineral acids, combines with the leather fibre, upon
which it exercises a most disastrous and disintegrating
action, and to the use of this acid, either as a bleaching or
clearing agent in the tanning process, or in subsequent use
in developing the colour in the dye-bath, may be ascribed
the cause of decay of over 90 per cent. of modern bookbinding
and upholstering leather. It is impossible to
remove these acids from leather by any subsequent amount
of washing, or without the addition of some other chemical
to expel them. Recently the writer treated some
leather with sulphuric acid, and after cutting the leather
up into small pieces, washed the same in running water
for three weeks; at the end of that period the sulphuric
acid was still tightly fixed in the fibres of the leather.
The introduction of aniline dyes instead of the older
process of wood dyes made a great change in the production
of bookbinding leather. Hundreds of new shades
of colour were produced, and the process of leather dyeing
was simplified and cheapened. But, unfortunately,
in the use of a certain class of these dye-stuffs the full
depth of shade could not at that date be produced upon
the leather except in the presence of an acid. Here,
again, therefore, sulphuric acid was introduced into the
leather during the process of manufacture, thus increasing
the proportion of leather which contained this
disintegrating material. It has frequently been stated
by leather dyers and others that a certain quantity of
sulphuric acid must be used with acid dye-stuffs, otherwise
the full depth of shade cannot be produced, and
they claim that without its use it is impossible to
produce certain brilliant shades of colour. These statements
have been proved to be devoid of foundation.
There are several substitutes for sulphuric acid which are
harmless in their nature. Among these I may mention
formic, acetic and lactic acids. These are organic acids
which have no harmful action on the leather; they are
easily washed out, and even if any trace of these acids
be left in the skin, they will evaporate. Formic acid
has even been proved to be cheaper than sulphuric, and,
moreover, is capable of developing equal shades in all
cases, and deeper and more brilliant shades of colour
with some dyes. For the present, however, bookbinders,
and especially librarians, are advised not to insist upon
brilliant shades of colour.
The introduction of the splitting machine and the
introduction of a machine for shaving leather has undoubtedly
tended to produce a large quantity of thin
leather, but it is impossible either to shave or to split
a skin without cutting the network of fibres, and the
strength of the leather cannot but be materially decreased.
Leather is made up of a complex system of fibres interweaving
and intertwining in every possible direction, and
even the small amount of paring carried out by the bookbinder
himself considerably impairs the strength and life
of the binding. How much more, therefore, does the
splitting and shaving that the tanner carries out in order
to bring the skin to an even substance destroy the strength
of the product.
Sufficient has been written on the printing of morocco,
seal, and pig grains upon skins of an inferior class, but it
cannot be too strongly pointed out to librarians that
the strength of embossed leather must be impaired when
it is realised how the embossing and printing is carried
out. The skins to be embossed are coated over in the wet
state with a mixture of dye, size, and other materials,
and are then passed between two hot electrotype rollers.
This embosses or prints upon the skin the required grain;
at the same time it glues the fibres of the leather together,
preventing the free run which good skins should possess,
and the heat dries up the leather, reducing its strength
very considerably.
I now come to the stripping, scouring, souring, and
re-tanning of leather. It is difficult to decide whether
more damage is done in this process or in the use of
mineral acids in the dye-bath; but it is certain that any
leather which is stripped of its natural tanning by use of
alkalies or bleached by an acid has lost at least 90 per
cent. of its wearing and lasting properties. Thousands of
dozens of skins in the rough tanned condition reach the
English market from India, Australia, New Zealand, and
other parts. These are tanned with quebracho, mimosa,
or some similar tanning material, whereas the Indian
skins are nearly all tanned with turwar bark and are
of a reddish-fawn shade of colour. These are purchased
by the leather finishers, and are manufactured in England.
In order to get rid of the reddish colour they are first
soaked in water and afterwards drummed in a weak
solution of washing soda, borax, or some similar alkali.
This removes the uncombined tan from the skin, as well
as taking out the natural grease. The skins emerge from
the drum a dark mahogany colour; they are then washed
in water and afterwards soured in a sulphuric acid bath.
This bleaches the skin to a light bright shade. The
finisher then, in order to put back tannin into the skin
of a light colour, re-tans them in sumach or a mixture of
sumach and oak. They are now known as re-tanned
skins; and after drying, are dyed and finished in the
ordinary manner. The sheep and goat skins are sold as
roans or moroccos, as the case may be, and, as a rule, no
indication is given that these are re-tanned skins. The
re-tanned Indian skins, however, generally leave the
factory as persian roans or persian morocco, but as the
skins pass from the manufacturer to the merchant, from
the merchant to the small dealer, the word “persian”
is generally omitted, and they reach the bookbinder as
moroccos or roans, as the case may be. Now this is the
most important point for the binder. I would go so
far as to say that it should almost be a punishable
offence to use either persians or re-tanned skins for
bookbinding purposes, as such leather cannot possibly
last ten years if exposed to light and air. Not only has
the scouring and alkali a perishing effect upon the
leather, but it is afterwards made worse by the treatment
with acid, a bleach, and the further addition of acid to
the dye-bath; added to which the alkaline treatment
removes the natural grease or nourishment of the skin,
and it is well known to those engaged in the leather
trade that the strength and life of a leather is at least
doubled by a proper nourishment of the leather with a
suitable fat. Therefore, if the whole of the natural fat
is removed, the leather rapidly dries, it loses its elasticity
and spring, the grain cracks, and after keeping in a dry
library for some time the backs break right off the books.
I have dealt with the eight chief causes of premature
decay, but before passing to the other part of this paper
I must also deal with the weaknesses of the bookbinder
as well as those of the leather manufacturer, and, for
reasons stated above, absolutely condemn the undue
paring of leather, the bleaching of leather by means of
oxalic acid, and the use of patent finishes and glares, the
composition of which is in most cases a mystery, many
of them containing acids, others containing drying
agents which have almost as injurious an action upon
leather as the vitriol used by the tanner.
To revert to my original thesis, it is not only possible
to obtain a leather as good as any leather manufactured
from the 16th to 18th century, but it is even possible to
get a better leather. Librarians, in drawing up their
binding specifications have only to do what the Controller
of H.M.’s Stationery Office is doing for the
libraries under his charge, viz., to provide under suitable
penalties that leathers supplied by the contractor shall
be equal to samples shown on pattern cards prior to
tendering for the contract, and in addition to insist
that such leathers shall conform to certain conditions laid
down in the Report of the Society of Arts’ Committee on
Bookbinding, which may be summarised as follows:—
1. The binder undertakes not to use stripped and
re-tanned leather, whether persians (East Indian
skins) or from elsewhere, or to use leather
embossed or grained artificially to resemble
morocco, pigskin, &c.
2. He guarantees (or undertakes to produce the
guarantee of the firm supplying the leather)
that all skins supplied (1) are genuine as
described; (2) are tanned with pure sumach or
galls, or in the case of calf or sheep with
oak bark, or mixtures of oak bark and sumach;
(3) that no mineral acid has been used either in
the process of tanning, bleaching, or dyeing,
and that the leather is free from acid or other
injurious ingredient; (4) that he will use no acid
to clear the leather in the process of binding.
Before drafting his binding specification the librarian
would do well to consult the excellent “Note on Bookbinding”
by Mr. Douglas Cockerell, published by W. H.
Smith and Son, at the price of 1d. Special attention is
drawn to the difference of the cost in binding according
to Specification I. and II. of the Society of Arts’
Committee reproduced on pp. 20-22 of this pamphlet,
and to Mr. Cockerell’s remarks on pages 9, etc.
The above stipulations should not make any substantial
difference in price per volume to those libraries
which already have been using high-class leather tanned
in sumach, but librarians who have hitherto been content
with persians, re-tanned Australians, and other cheap
classes of leather must expect to pay a higher price
for leather, properly tanned and guaranteed to last.
Several large firms of high reputation, who are now
catering for the bookbinding trade, have already turned
out thousands of skins of a satisfactory nature. These
firms are not only anxious to fall in with the requirements
of the Society of Arts’ Report, but are desirous of
removing the distrust which at present exists with regard
to leather, and to reinstate this article as being the
standard and natural covering for books. For permanent
wear, whether for books or other purposes, leather,
when properly prepared, is without a rival both for
appearance and durability. It is only for the cheaper
class of work that leather substitutes are formidable as
rivals.
With regard to strengths of various leathers, it is
somewhat difficult to lay down a hard-and-fast rule, but
in general terms it may be stated that the strongest
leather made is pigskin. The fibres are tough, somewhat
coarse, but of great strength. The only danger is
in the paring down of the skin previous to use in the
binding, and therefore, by reason of its thickness, it is
well to only use pigskin for the binding of large, heavy
volumes where a thick leather can be used without
detriment to the appearance of the book. Seal probably
comes next in strength. It is tougher than goat skin,
and, by reason of the quantity of natural grease which
these skins contain, will in most cases remain pliable and
wear longer than the average morocco. Seal is closely
followed by goat skin. A special feature of goat is the
hard grain which it possesses. This is specially to be
recommended where much frictional wear is given to the
book. Sheep and calf may be put on about the same
footing. Both are extremely pliable, but I think one
may safely state that books bound in sheepskin leather,
if that leather be from the cross breed, Welsh, or other
mountain sheep, will probably outlast calf skin. There
is no doubt that calf has got into disrepute largely on
account of the destructive processes used in the finishing
and production of the soft, smooth-grained calf, which
has of late years become so popular. Binders must
understand that the velvety finish can only be obtained
by an undue pulling down of the skin previous to the
tanning process or an undue paring on the part of the
binder. Both Russia leather and vellum, as binding
materials, have done good service in the past, but have
lost their old reputation for durability. For the present,
librarians are recommended to use these skins as little as
possible. A few words suffice to deal with skiver bindings.
These are the thin grain of sheep and sometimes calf,
and are at their best about equal in strength to thin notepaper,
their whole texture and fibrous structure having
been split off and their nature destroyed.
It must be understood that the deterioration of
leather is not only caused by faulty manufacture or
improper treatment in the dye-house or finishing shop.
Good bindings of sound leather are frequently destroyed
by the neglect of certain elementary precautions on the
part of the librarian. The subject is too large to deal
with fully in these pages, but librarians would do well
to study carefully the detailed report of the Society of
Arts’ Committee. But the following elementary rules
should be observed:—Books should not be exposed to gas
fumes, or to the direct rays of the sun; the temperature
of the library should not exceed 70° F., the upper strata
should be well ventilated, and a thermometer should be
hung on the same level as the top shelves in order to
advise the librarian whether the temperature is being
kept within reasonable limits. Freedom from damp is,
of course, an essential condition of library architecture.
The question of leather preservative compositions is
dealt with in another chapter, but too much cannot be
said against the use of various decoctions which are sold
to librarians for coating and preserving leather bindings.
Many of these contain turpentine, which has a drying,
detrimental effect. Various other emulsions are on the
market, but although these give the leather a soft,
pleasant feel when applied, this soon dries up, the
leather becoming hard and liable to crack. There may
be some suitable ingredients for applying to leather
bindings, but I am of the opinion that if a library is
not allowed to get too hot, and a plentiful supply of pure,
dry air is always present, sound leather should require
no further preservative.
