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Subject: Saliva


From: Rosemary Yallop <rosemary>
Date: Thursday, April 25, 2002
Sanchita Balachandran <sb381 [at] nyu__edu> writes

>I'm interested in finding out "recipes" for synthetic saliva.  I'm
>planning on using this to clean dirt from a marble sculpture.

In order to synthesize saliva for cleaning purposes, one first has
to have a clear view of which of the ingredients of natural saliva
is operative in the cleaning process for a given material.

Saliva is complex and its composition is extremely variable even
within one individual. Its pH, for example, varies with the rate of
flow and the duration of stimulation of the salivary glands, as does
the concentration of bicarbonate ions. I looked into the cleaning
action of saliva as part of my research project into cleaning vellum
and parchment for my Conservation MA at Camberwell. I do not doubt
the efficacy of saliva as compared to, say, water alone, but
understanding the precise nature of its action is rather more
difficult. Much of the evidence is anecdotal and results difficult
to quantify.Many descriptions focus on the enzymatic activity of
amylase in the hydrolysis of starch as the operative agent in
cleaning. This seems to me to ignore i) the relative success
obtained in removing proteins (typically old animal glue) and ii)
the possible contribution of other constituents (glands in the mouth
also secrete lipase, for example, although it is activated only in
the stomach where the pH is lower).

My personal view is that the chemical action of saliva may be
overrated compared to a simple poulticing effect. The glycoproteins
which give saliva its characteristic sliminess bring moisture into
contact with the object for long enough to facilitate mechanical
removal of surface dirt by swabbing, without, in the case of
parchment, over-wetting the object. However, this is purely a
hypothesis:if the nature of the cleaning action could be analysed
and understood in full, then obviously a synthetic substitute would
meet all the practical problems and underlying concerns
(particularly bacteriological) about the use of saliva.

Saliva has been used intuitively over the years (even if not always
admitted to). I would welcome the opportunity to share any other
views on this interesting and rather under-researched subject.

Rosemary Yallop
Book conservator in private practice

                  Conservation DistList Instance 15:74
                    Distributed: Friday, May 3, 2002
                       Message Id: cdl-15-74-001
Received on Thursday, 25 April, 2002

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