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Subject: Leather dressing

Leather dressing

From: Wim Smit <wim.smit>
Date: Wednesday, October 16, 1996
Regarding the various statements given recently concerning pros and
cons of leather dressing, we would like to contribute the following:

Leather dressing has been subject to vastly differing opinions.
There has been (is, I imagine) a large contingency of
conservators/restorers/collectors who hold the view that most
leather bindings will benefit from regular treatment with a
dressing. The dressing being composed of varying substances. There
is also the view, put forward most clearly by Toby Raphael and Ellen
McCrady, that leather dressing on books doesn't serve any purpose at
all and may even be damaging to the material.

Finally, there's a more differentiated approach like the one put
forward by Nicholas Pickwoad (28 Jan. 94) where he says that 'it
(leather dressing) isn't a cure-all, it isn't simple, but it can
help in the right place at the right time on the right skins'.
Interestingly, Pickwoad in his contribution stresses a point that is
I believe of major significance. He says that leather remains
flexible through moisture and that the oils and fats in the dressing
help lubricate but do not in itself give flexibility to the leather.

The important role of moisture is also obvious in the work of other
conservators like Mrs. Puissant of Ascona, who at one time describes
how she uses moisture (conditioning) as a sole means of conservation
for a leather binding. It's more or less Pickwoad's philosophy which
is also at the heart of the 'Guidelines for the Conservation of
Leather and Parchment Bindings' published earlier this year by the
Koninklijke Bibliotheek (the national library of The Netherlands) in
conjunction with the Central Research Laboratory for Objects of Arts
and Crafts (Centraal Laboratorium voor Onderzoek van Voorwerpen van
Kunst en Wetenschap).

In it a procedure is introduced which enables a restorer or
conservator to determine different types of damage to bindings by a
close examination of each book separately. He or she can then
select a treatment from a number of recipes given in the guidelines.
This means that we have left the practice of prescribing one
standard treatment that is considered applicable to virtually all
leather bindings. We feel that this practice tended to favour the
treatment of all bindings indiscriminately and in their entirety,
irrespective of the question whether each one of those books really
needed any treatment at all. As a consequence, in the past on quite
a few leather bookbindings dressing was applied too vigorously,
causing demonstrable problems.

Another feature of the new guidelines is the attention that is now
given to parchment, the treatment of which had almost entirely been
neglected in the past, even though it seems undeniable that many
parchment bindings may need just about as much preservation as does

In order to be able to assess the condition of a particular binding,
and, based on that assessment, also choose the right treatment for
that binding, we indicate for the benefit of the restorer a number
of relatively easy to carry out tests for the determination of the
pH and the ammonious sulphate contamination--two parameters which
show whether a given binding is deteriorating and whether a
buffering agent is required.

We now also hold the view that the best results when treating
leather and parchment are attained at 70% RH. At relative humidities
lower than that the fatty substances do not seem to penetrate
leather and parchment well. Low RH also implies a low moisture
content of the binding material, and an insufficient moisture
content is quite adverse to leather or parchment, weakening the
binding's textural strength and speeding up the concentration of fat
in the very surface of the binding material, where it is in fact
least needed. In the guidelines we therefore recommend conditioning
the bindings to be treated, i.e. exposing them to at least 70% RH
for several days.

To summarize, in the past questions have been raised as to the
effectiveness of leather dressing, even its adverse effects. We have
come to the conclusion that conservation of leather and parchment
bookbindings should never be a routine-like operation. There may be a
problem with leather and parchment bindings, or not. That is
something to be established by a professional restorer or
conservator. Leather and parchment will discolour with the passing
of time and will loose some of their flexibility, that's only
natural and as such no reason for large-scale treatment. It is only
when it is obvious that the material is breaking down or that the
flexibility is no longer there where it is needed, for example on
the spine or the hinges of books, that it may be necessary to act,
and then sensibly.

Those who are interested in obtaining a copy of the guidelines
(Dutch title: Richtlijnen voor de Conservering van Leren en
Perkamenten Boekbanden) should contact the Koninklijke Bibliotheek
at P.O. Box 90407, 2509 LK, The Hague, or the Central Research
Laboratory at Gabriel Metsustraat 8, 1071 EA, Amsterdam. It is
advisable to do soon, as it threatens to sell out.

Wim Smit
Head, Conservation Department
Koninklijke Bibliotheek
P.O. Box 90407
2509 LK  The Hague
The Netherlands
+31 70 314 0569
Fax: +31 70 314 0450

                  Conservation DistList Instance 10:39
                Distributed: Wednesday, October 16, 1996
                       Message Id: cdl-10-39-002
Received on Wednesday, 16 October, 1996

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