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Re: Wheat starch paste



The ratio of one part wheat starch to 5 parts of water makes a good, thick
paste.  However, I do not recommend using a microwave to prepare it because
the starch granules do not have time to absorb enough water to burst the
membranes.

You can feel a grit in microwave paste which is not present in adequately
cooked paste.  Compared under a microscope you can see that the difference
is undercooked starch granules in the microwave paste.

A conservator, during the 1970's, published his recipe for adding 10% of a
PVA known as Jade 403 to wheat starch paste.  It does possess the advantage
of increasing tack to the mixture and it is somewhat reversible.  The
adhesive bond can be swollen/dissolved with water, leaving a 10% residue to
remove mechanically.  Since this is likely to damage original material, I
don't use PVA except on boxes/slipcases, or , perhaps, when recasing a
modern book.

But I do not refer to adhesive mixtures which contain PVA as archival.  If
you plan to add PVA to paste, do it when you are ready to use it, not when
you are cooking or storing it.

PVA contains a little bit of formaldehyde to retard mold growth, but it
doesn't prevent mold growth, as anyone who has seen mold growing in a
container of it can attest.

I cook my paste in a double boiler.  When it is done, I pour it into a
container of water.  This eliminates the skin which will form on it if you
pour it into a dish.  If the water becomes cloudy I know that the paste
wasn't cooked enough.


There are two main mixtures which I use.  I'll add cooked wheat starch
paste to hide glue to increase the tack, and flexibility of the dried bond;
and methyl cellulose (generally a 2% solution) to wheat starch paste for
the same reasons.

The proportions vary according to my judgement of what will work best for
the job at hand.

Hope this helps.

Jack

Jack C. Thompson
Thompson Conservation Lab
7549 N. Fenwick
Portland, OR  97217

voice/fax: 503/735-3942

www.teleport.com/~tcl/


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