Re: Salt and Textiles

[Constance <cnstnce@xxxxxxxxxx>]

On Oct 19, 2004, at 2:38 PM, Carine Gengler wrote:

> Has anyone ever dealt with the problem of salt on/in textiles?


I highly recommend the disssertation by Glenda Susan Marsh-Letts, Univ.
of Western Sydney, 2002, "Ancient Egyptian linen: the role of natron
and other salts in the preservation and conservation of archaeological
textiles"  This can be downloaded in 16 pdf files from

http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20031219.155140/

It is a great document with value for all textile conservators.

I would also be interested in any replies to Carine's query.  From my
experience,  I would say that most changes that occur when salt-laden
textiles are brought out of the dry conditions of burial are due to
increased moisture regain in the fibers.  Sodium chloride crystals on
and in the textile deliquesce.  Some textiles feel clammy or are
positively wet.  Through the salt's hygroscopic activity, textiles
become more flexible, but they lose strength.  As textile structures
become more mobile, physical damage can occur more easily in handling
the weak fibers.  Chemically, the chlorine ion will become active in
the moist textile - this is particularly worrisome for archaeological
silk.

Carine, what kind of damage have you observed?

There are a variety of salts associated with archaeological textiles -
notably metallic salts of chlorides, carbonates, sulfates and nitrates.
 Most are not hygroscopic - or very hygroscopic.  Usually, deposits on
textiles are some mixture of several of these.  Removal involves a
variety of strategies - chemically and physically.  Crystal formation
can physically distort the weave (I have observed this in Han, Jin and
Yuan silks on a micro level).  Sometimes crystals displace pigments
(observed in Paracas shellfish purple painted textiles).  And
occasionally there is a mystery: large sodium chloride crystals can
sometimes resist solubilization - even in warm de-i water (I checked
with EDS to confirm microscopic identification of sodium chloride) -
and can be too hard to break and disperse into smaller bits without
damaging the textile.

Understanding the interaction of salts on archaeological textiles (in
post-excavation humidities) is fundamental to establishing
decision-making criteria for wetcleaning.

David Walker
Talisman restoration, Inc.