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Re: Starch Pastes



The starch pastes ARE acidic.  The level of acidity will vary with the
source and processing and preparation.  It is for other qualities, some of
which Kathy Hamre pointed out, that starch pastes are so well used,
especially in the book and paper conservation fields.  Some professional
conservators use only the most refined, precipitated, processed dry powder
pastes to ensure the best quality; others even add alkalined water to
off-set potential acidity from the paste.  I wonder if adding alkalinity
does not undermine the strength of the adhesive bond (I don't know, just a
gut feeling), although some will argue that the pastes are too strong for
what we use them for anyway, so weakening them would be advantageous.

Some conservators feel that the pastes aren't very flexible (and other
things) in the long run, so add cellulose ethers (e.g. methyl cellulose) to
the adhesive mix.  My personal experience is that the mix is synergistic and
EXTREMELY difficult to undo --very different than perhaps what was intended.
Of course, sometimes this is a good thing!  However, some of the mixes
require a much thicker percentage and application of paste than I might have
used if just using a straight paste application, so wonder how flexibility
is being improved.

The dangers of acidity to paper has been well established and it's great
that folks are so contentious about it, desiring to do the best.  However,
"pH" and "acid-free" have become convenient sound-bites and people have
forgotten or missed the bigger understanding of the intricacies inherent in
materials.  I've even seen "acid-free" used as advertising ploys on
plastics!  From what I have been able to gleen from scientists, this is like
a "cholesteral free" label on rice cakes.

Stephanie Watkins
swatkins@xxxxxxxxxxxxxxxxxxxx

At 05:32 PM 3/25/97 -0600, you wrote:
>Terrence Collins wrote:
>>I'd like to ask some follow up questions to your recent posting.
>>What kind of "paste" do you mean?  If wheat paste, isn't it acidic?
>>And are pastes as flexible as pvas in the long run?
>
>Kathy Hamre wrote:
>Wheat starch paste is not acidic, and it is the adhesive of choice in the
>conservation and making of archival materials, books and artworks.
>Wheatstarch paste is relatively flexible, and is usually present in a thin
>layer which does not cause any problems to the flexibility of a book spine,
>for example.
>
>As Terry Belanger pointed out in his post, removing PVA is difficult to
>impossible to remove without doing significant damage to the original
>materials.  Wheat starch paste is easily reversable amd does not damage the
>original materials.


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