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Re: Starch & Flour Pastes



I would like to raise some queries regarding the recent messages on this topic.

Is starch paste naturally acidic, or does it become so after preparation, or
after some years on the pasted object combined with the effects of the
atmosphere, changes in temperature and humidity, etc?   I am not a chemist, but
I had never thought of starch as acidic trying to remember my A-level school
chemistry, or are there stabilisers or other constituents in the material as
purchased?  Or does the paste breakdown within a short period of making it
moist to acidic components?  Brady's 'Materials Handbook', McGraw-Hill, does
not suggest starches as acidic.

The paste used by binders in past centuries must have been just ordinary flour
from the mill, without any thought of 'acidity', using local water which may
have been acidic or alkaline depending on its source.

I recently found the public water supply in my area in the UK is quite
alkaline, some 140 ppm of Ca++, but I had generally made in any case my paste
with CaOH solution. (The water has a large number of other constituents in it,
but that's another story!).  This was more of a future safeguard against long
term effects, rather than a belief that the paste was acidic.

I have normally purchased a 2 lb bag of strong flour (originates in Canada?)
from the local supermarket rather than ordinary plain flour, which I always
understood to make a weaker paste owing to the lack of gluten.  Is this another
misconception of mine?  I now wonder if this bread flour, in fact, has any
undesirable constituents from a manufacturing and shelf life  point of view?
There is nothing listed that I recall on the bag.

I also occasionally raid my wife's kitchen cupboard for corn-flour which makes
a very satisfactory, almost colourless, paste for paper repairs.  Is this a
suitable starch, or should I be concerned for its 'acidity' also?

I also use 'Stadex', a cold water starch paste, but again I generally prepare
it with calcium hydroxide solution.

I have a 1787 book with small engravings, about 2" x 2", on India paper.  These
are stuck down by their corners to each text leaf.   I cannot see the paste as
there is no visible reaction even after 200 years.   I have carefully lifted
one engraving in a water bath in order to clean the text leaf.   The tissue
lifted successfully, but there is no obvious mark or reaction from the paste,
so was it a wheat flour paste, perhaps thinned down?

As I repair old books advice would be welcome.

Rodney Fry,
Berks., UK
<  rod.fry@xxxxxxxx  >


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