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Re: Starch & Flour Pastes

Rodney Fry wrote:
>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?

Wheat starch paste is slightly acidic.

>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.>

I'm not a chemist either, but I have been told that paste often PH tests
slightly 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 would guess that you are correct, so the alkalinity of the natural water
must have neutralized it enough, as you suggested.

>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?

My recollection is that the regular flour in GB is self raising/rising and
therefor brobably containg baking soda or baking powder.  So you are
probably better off buying the *strong* flour, but you might want to chech
out a health food store and see if they have wheat starch.  I can get it
quite cheaply here in Canada in any health food store.  I have never used
corn flour, but I have used corn starch, which works very well.  Rice starch
is an option too.  Oriental food stores would carry it (although they are
hard to fin in London - I had to look long and hard to find one near Covent
Garden I think)

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

I'm not familiar with this.

>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?

If paste is doing its job you shouldn't be able to see it, and it should not
leave any mark, other than a bit of gloss on the paper.  This sounds like
paste to me.

>As I repair old books advice would be welcome

I'm happy to give advice from my experience, but I can't say that it is the
only way to do things, it is what works for me, so far.

Kathy in Saskatchewan Canada


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