Leather dressing

Sent by Angela Thompson, National Gallery, London, on behalf on
Margaret Hey who is not on the List.

    Wim Smit's contribution (Conservation DistList, Instance: 10:39,
    October 16, 1996) gives me the opportunity to round out and link
    together several of the experiences he reported.

    In early 1971 (or perhaps later 1970) Christopher Clarkson and I
    visited Dr. Ronald Reed (he of the book) in Leeds to discus
    bookbinding skins and leather dressing.

    He emphasized for us the great importance of water in giving
    flexibility to skin (a concept not so well appreciated then as
    it is now, some 25 years later).

    He explained that leather dressing served to lubricate the
    fibres so that they move one over another more easily and would
    also help to a) retain moisture within the skin structure, and
    b) prevent or at least slow down the penetration of pollutants
    from the atmosphere.

    However, full benefit would only be obtained if some moisture
    had been put back into the skin before applying any leather
    dressing.  Ron therefore advised that books should be kept in a
    more humid environment before applying any dressing.

    I don't think this information has ever appeared in print
    although I have always subsequently taught it.  It doesn't
    contradict any of the individual pieces of information supplied
    by Wim Smit but simply links them together while giving due
    credit to the originator.

    One other point--the disagreement over the value of leather
    dressing stems from the time when mixtures contained potassium
    lactate--a substance over which there was at one time
    considerable controversy.

    Again, Ron Reed explained that applying potassium lactate to an
    acid (degraded) skin would release lactic acid.  Like acetic
    acid, lactic acid can swell collagen fibres and thereby make
    them more vulnerable. However, unlike acetic acid, lactic acid
    is not very volatile so that repeated applications of the
    leather dressing would lead to a build-up of lactic acid--not a
    good thing.

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                  Conservation DistList Instance 10:49
                Distributed: Thursday, November 21, 1996
                       Message Id: cdl-10-49-001
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