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Re: [BKARTS] Leather conditioning

Perhaps all leather "dressings" are hydrophobic, as
you say, but not all leather preservation treatments

Ed,  bookrestoration.net

--- "Jack C. Thompson" <tcl@xxxxxxxxxxxx> wrote:

> It would be very nice if a conservation lab
> somewhere set
> a chemist to studying the question of leather
> deterioration,
> leather dressing, and leather tannage for
> permanence.
> Some years ago such an attempt was made.  At the
> request of
> the British Library the British Leather
> Manufacturers Research
> Association (BLMRA) designed a serious research
> program and
> sent a prospectus to national libraries around the
> world, and
> to major research libraries, seeking monetary
> support.
> In the end, only the British Library was willing to
> contribute
> money to the project.  The project went ahead, but
> the research
> goals were greatly narrowed, and resulted in a
> publication which
> recommended vegetable tannage with aluminum
> triformate re-tannage.
> That produced a leather with good prospects for
> permanence, but
> bookbinders did not much care for it at the time.
> So, we have to fall back on published literature
> from a variety
> of sources, integrating what we read with the
> deteriorated books
> in hand, and making the best decisions we are
> capable of at the
> time, realizing that sometimes we will be wrong.
> So.
> The old British Museum leather dressing was
> originally developed
> for highly humid areas, such as parts of India, etc.
> where the
> British Empire had records offices, and sometimes
> the formula
> could contain a small amount of DDT to help control
> bugs; the use of
> thymol sprays was developed to fight mold in those
> same areas.
> The lanolin-neatsfoot oil formula was originally
> developed as a
> leather dressing for harness and saddles, and was
> published as a
> U.S. Dept. of Agriculture circular.
> Acid, esp. sulfuric acid, has been blamed for most
> of the problems
> afflicting leather.
> Whether added to the tan bath (from about mid-19th
> century) to
> accelerate tannage, or as a contaminant in
> illuminating gas, when
> gas lights were in homes, businesses, and libraries.
> This information was made clear in a 1901 (reprinted
> in 1905) _Report
> of the Committee on Leather for Bookbinding_, a
> British committee.
> They also identified ammonia fumes as part of the
> problem, but in
> general, only acid has been remembered.
> A few years later, in the Technologic Papers of the
> [U.S.] Bureau of
> Standards there were two articles: "Determination of
> Sulphur in
> Illuminating Gas," by R.S. McBride and E.R. Weaver.
> No. 20, March 7, 1913.
> The following year J. D. Edwards published
> "Determination of Ammonia in
> Illuminating Gas,"  No. 34, March 2, 1914.
> The effect of acid is to harden and embrittle
> leather, through removing
> moisture which is required to maintain flexibility.
> The effect of alkali (such as ammonia) is to soften
> leather and make
> it powdery.
> When an acid and an alkali come into contact they
> neutralize each other
> (more or less) and the result is a salt.  Salts are
> deliquescent (they
> dissolve under humid conditions and crystalize under
> dry conditions)
> and wherever they crystalize they can weaken or
> break leather fibers.
> Leather dressings have one thing in common; they are
> hydrophobic.
> If a leather is flexible it contains enough moisture
> to stay supple
> and a dressing will act to retain that moisture and
> prevent additional
> moisture from being absorbed.  A balanced condition.
> If a leather has become inflexible or powdery, it
> lacks moisture (among
> all its other problems) and if any leather dressing
> would help, it should
> be one which adds moisture to the leather.
> But leather in that condition can easily be
> destroyed by moisture.
> No clear answers, but maybe a little (non-gas)
> illumination of the problem.
> Jack
> Thompson Conservation Lab.
> 7549 N. Fenwick
> Portland, Oregon  97217
> 503/735-3942 (phone)
> 503/289-8723 (fax)
> http://www.teleport.com/~tcl
> "The lyfe so short; the craft so long to lerne."
> Chaucer  _Parlement of Foules_ 1386
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