Treatment of bookbindings
Formulas for cleaning, deacidifying, strengthening, lubricating and removing stains from leather bookbindings
have appeared in various publications, especially since the beginning of last century. Although we would not
now be inclined to call many of these treatments conservation, they were often intended as such at the time.
They involved all manner of materials, some of which have unintentionally adversely affected the condition of
the leather. Most formulas were intended to be used on leather bookbindings, but there is evidence that certain
formulas, for instance for cleaning and lubricating, were also applied to parchment bookbindings. The following
is a concise survey of the various treatments applied to bookbindings in the past.
Cleaning
Leather was initially cleaned with whatever domestic products were to hand: turpentine, petrol, eau-de-Cologne,
even skimmed milk, but most of all soap. Gradually special leather-cleaning soaps made their appearance.
Saddle soap (Propert's Leather and Saddle Soap), developed in the nineteenth century specifically for
cleaning leather, was recommended for scrubbing leather bookbindings. It was also marketed as a dressing for
utilitarian leather such as harnesses. Its main ingredient is a mixture of lubricating and cleaning products.
Leather treated with this soap is very alkaline (pH 9-10). Regular treatment with soap produces a hard,
darkened and broken grain; it also allows the dirt to penetrate deeper into the leather so that the grain becomes
clogged with dirt, soap and an excess of fat. Edel's book (1946) contains a formula for making stearin soap, but
the disadvantage of this soap is that in leather with a high pH value it may lead to the formation of sodium
sulphate. This salt sometimes rises to the surface, leaving a white deposit on the leather. The same author
recommends a formula of hard soap, water, ammonia, glycerine and ethylene dichloride. A woman writing in the
English periodical The Housekeeper's Week in 1908 recommends cleaning leather bindings with
pulverised pumice applied with a cotton cloth. Leather bookbindings treated in this way may well have been
clean but they would also certainly have been worn off!
In addition to general cleaning agents there were also formulas for removing stains. Impurities were bleached
with oxalic acid. Chloramine-T, sodium hypochlorite and hydrogen peroxide were also used. Greasy spots
could be treated with magnesium oxide. To remove mildew a thick dressing of sodium bicarbonate and water
was put on the leather, which was then hung out to dry in the sun.
Apart from the detrimental effect of certain chemicals, these formulas have the additional disadvantage of
containing water. In some cases, for instance when acids are present, this may cause the leather to turn black.
There is also a risk that the leather may swell.
Once conservators became aware of the problems they switched to safer cleaning agents, such as non-ionic
soap dissolved in alcohol, trichlorofluorethane and other hydrocarbons.
Dressing and oiling
All manner of oils and dressings have been used to make up for a possible deficiency of fat in the leather, and
to give it a polished exterior: beeswax, butter, cedar oil, coconut oil, glycerol, Japanese wax, candle grease,
neatsfoot oil, olive oil, paraffin, castor oil, shoe polish, tallow, vaseline, spermaceti (a fatty substance from the
sperm whale), wool fat (purified sheepskin fat, anhydrous lanolin) and the previously mentioned saddle
soap.
Many of these oils and dressings are too viscous to penetrate deeply into the leather and so remain on the
surface. They seal off the leather and prevent it from 'breathing'. This is also true of (pure) beeswax, a product
unfortunately still recommended today. Another disadvantage of lubricants (e.g. coconut and olive oil) is that
they are prone to oxidise. This leads to discoloration and hardening of the leather and may cause organic
acids to be released in the leather. Moreover, overfatting, in ousting the moisture from the leather, disturbs the
natural water balance.
A 1909 formula recommends the use of vaseline and olive oil for lubricating dried-out leather, while shoe polish
is one of the substances recommended to restore the gloss. Shoe polish was also thought to act as an insect
repellant.
Other products besides oils and dressings have also been used to restore the gloss to dried-out leather.
Well-known agents are egg white, egg yolk, and starch mixed with either water or milk. The bindings were
rubbed till they shone, probably in ignorance of the fact that here, too, water was potentially damaging.
The above-mentioned formulas were used for a very long time, even after products based on research into the
structure of the leather and its maintenance had reached the market. Just one example of the incredible
rashness with which people set to work is this 1956 formula: 'First use a solution of starch in water, then saddle
soap and neatsfoot oil, then more starch and water, then leather or starch polish' (Rhodes, 1991). No doubt the
book subsequently shone like a mirror but whether the leather survived such drastic treatment is another
question.
At the British Museum HJ Plenderleith's study of leather dressings led him to develop the British Museum
Leather Dressing which has since been used in many variations by conservators. The basic formula contains
the following ingredients: 200 gram lanolin, 30 ml cedar oil, 15 gram beeswax, and 350 ml hexane. Sometimes
60% of the lanolin was replaced by neatsfoot oil. One disadvantage of the solvent hexane is its tendency to
evaporate rapidly. Before the fat/hexane mixture has been able to penetrate deep into the leather the hexane
evaporates to the surface of the leather, taking most fat with it. While beeswax prevents air pollutants from
penetrating the leather it does this by closing off the leather, thus disturbing the water balance and causing the
leather to dry out. Almost all formulas published below, including those in the present publication, are based on
the Plenderleith's formula.
The British Museum Leather Dressing was part of an elaborate leather conservation programme. Other steps
entailed cleaning the leather, if necessary with soap and water, and applying an aqueous solution of 7%
potassium lactate as buffer. A warning was given about the dangers of using too much lactate which made
books sticky and could cause fungal growth. The books had to be absolutely dry when the leather dressing
was applied (Plenderleith, 1946).
Disinfecting
Besides such well-known substances as thymol and methyl bromide, a wide range of fungicides and
insecticides have been used to disinfect leather during the twentieth century. An extensive list can be found in a
publication of The Leather Conservation Centre (Calnan, 1985).
Strengthening
The most popular agent for strengthening and glueing leather bookbindings was starch. 'Take a small amount
of starch and rub this carefully into the parts that need it. When it has dried, treat the whole binding carefully with a
thin layer of glue,' was the advice given in an 1856 manual (Rhodes, 1991). Later on adhesives based on
synthetic resin, such as polyvinyl acetate, were also used. A 1956 manual recommends filling little tears in the
leather with undiluted plastic cement (Rhodes, 1991).
On occasion, leather bindings have been treated with varnishes and later with acrylic and epoxy resins, etc.,
applied by brushing, spraying, injecting or a bath.
Since 1987 the Central Laboratory has recommended using a polyurethane resin (a polymer dissolved in a
mixture of hydrocarbons) as a fixative for loose leather flakes. However, this should only be used as a last
resort, since it is irreversible.
Conservators in the United Kingdom nowadays use a synthetic polymer (Plaintex) based on ethyl acrylate, also
dissolved in hydrocarbon, to fix loose and decaying parts of leather. This treatment is reversible.
Another, relatively recent, method of strengthening and consolidating leather bookbindings involves retanning
with aluminium salts. (The Conservation of Bookbinding Leather, London, British Library, 1984)
Deacidification
The tanning process usually leaves leather with a low pH value (i.e. high acidity). This is all right as long as the
value does not fall below pH 3; anything lower will certainly have a negative effect on the leather. When this
happened the leather was 'deacidified', that is to say, the pH value was raised. To achieve this the book was
placed in a closed area, over a small tray containing ammonia (15%), and left for 15 minutes. A potassium
lactate solution of 7% has also been used to neutralise the sulphuric acid in the leather.
At present the use of potassium lactate is discouraged, while the use of ammonia and/or buffering is restricted
to certain damage categories. Details of the approach recommended today are described in the present
report.
Literature
Calnan, C.N., Fungicides Used on Leather. London, The Leather Conservation Centre, 1985.
Calnan, C.N. 'Retannage with Aluminium Alkoxides - a Stabilising Treatment for Acid Deteriorated Leather', in:
Internationale Leder- und Pergamenttagung, Offen-bach am Main 1989, pp. 9-25
The Conservation of Bookbinding Leather. London, British Library, 1984.
Cunha, G.M. and Cunha, D.G., Conservation of Library Materials I. Metuchen, N.J., 1971.
Edel, L.P., Mengen en roeren, vol. 1. Deventer, 1946.
An Expert. The Book of Trade Secrets - Receipts and Instructions for Renovating, Repairing, Improving and
Preserving Old Books and Prints. London, 1909.
Goddijn, P.A., e.a., Richtlijnen voor het conserveren van leer en perkament van boekbanden.
's-Gravenhage, Koninklijke Bibliotheek/Centraal Laboratorium, 1987.
Henket, J.G.M., 'Conservering van leren banden', in: de Restaurateur, 4 (1974), 1, pp.5-6
Jackman, J., Leather Conservation. London, The Leather Conservation Centre, 1982.
McCrady, E., 'Research on the Dressing and Preservation of Leather', in: Abbey Newsletter, 5 (1951), 2,
pp. 23-25.
McCrady, E., 'How Leather Dressing may have originated', in: Abbey Newsletter, 14 (1990), pp.
19-20.
Plenderleith, H.J., The Preservation of Leather Bookbindings. London, British Museum, 1946.
Raphael, T. and McCrady, E., 'Leather Dressing: To Dress or Not to Dress', in: Leather Conservation
News, 1 (1983), 2, pp. 2-3.
Rhodes, B., 'Hell's own Brew: Home Book Renovation from Nineteenth Century Receipts to Today's Kitchen
Chemistry' in: The Paper Conservator, 15 (1991), pp. 59-70.
De Steen der wijzen. Algemeen receptenboek inhoudende 850 recepten voor allen en over alles.
Gouda, 1885.
Waterer, J.W., John Waterer's Guide to Leather Conservation and Restoration. Northampton, The
Museum of Leathercraft, 1986.