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Subject: Leather bloom

Leather bloom

From: Alan G. Howell <ahowell>
Date: Sunday, March 27, 1994
The reference work on leather that I have found to be very useful in
recent months is the edited proceedings of the first conference held by
the Leather Conservation Centre in August 1986 at Nene College,
Northampton, England.

    Christopher Calnan and Betty Haines (editors), Leather: its
        composition and changes with time, The Leather Conservation
        Centre, Northampton, 1991. ISBN 0 9460 7204 3.

The book is divided into two sections: the composition of skin and
leather; the deterioration of skin and leather. There are 14 papers.
Some of them (or variants on them) have appeared elsewhere. In this 90
page, accessibly written, publication they are efficiently brought
together almost as a "study guide" for conservators and anyone else who
encounters leather in their work.

In chapter 7, "Lubricants" A.W.Landmann talks about spue.

    "In the process of making leather it is essential, after tannage, to
    introduce a lubricant into the leather in order to prevent the
    resticking of the fibres as the leather dries out, and in this way
    maintain a degree of flexibility and softness... (p.29)"

    "Fats, oils  and waxes have all been used to lubricate leather...
    most of the natural fats and oils are triglyceride fats... (p.29)"

    "Triglyceride fats can become rancid breaking down into the
    constituent glycerol and fatty acids. This change is promoted by
    mould growth on leather. Free fatty acids that are solid at room
    temperature will tend to crystallise out on the leather surface to
    form a white spue. (p.31)"

    "A more serious form of spue is that which is formed as a result of
    the oxidation of drying oils.  This spue first makes its appearance
    as small spots of resinous matter on the surface of the leather but
    may become so severe as to form a resinous sticky coating. over the
    entire leather surface.  Oxidation of drying oils is accelerated by
    warm moist conditions and the presence of heavy metals.  The use of
    rancid drying oils will tend to give rise to fatty acid spues as the
    free fatty acids present oxidise more readily than the unchanged fat

Landmann then goes on to discuss the choice of lubricant with the
avoidance of spue in mind. He also has some excellent observations on
leather dressings and how they do--or don't--work.

Other papers are useful for their succinct descriptions of phenomena,
tests (such as PIRA) and conservation treatments that have become
commonplace in the literature of leather conservation.

The book is available from the Leather Conservation Centre, 34 Guildhall
Road, Northampton, NN1 1EW, England

Alan G Howell
Preservation Manager
State Library of New South Wales
Macquarie St, Sydney, NSW 2000, Australia.
Fax: 02-232-4816

                  Conservation DistList Instance 7:68
                  Distributed: Tuesday, March 29, 1994
                        Message Id: cdl-7-68-002
Received on Sunday, 27 March, 1994

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