message from 03 07 1996
"are you aware that starch and dextrin are not the same thing? Starch is a
chain of glucose monomers (amylose and amylopectine) and dextrin is the
same base but hydrolised with hydrochloric acid. This changes the
properties dramatically. Shorter chain structure, lower molecular weight,
other water retention, more soluble in water, tendency to form brittle
"films", forming sugar like crystals etc. Therefore I suggest that we use
the word starch for wheat- corn- or rice starch made of starch granules
(flour without the gluten) and dextrin (also known as British gum) for the
hydrolised version of starch."
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normal homemade starch will be a greyish translucent gel which will be
hardly visible on drying. Dextrine is a rather stiff white mass that will
release water from its structure when worked with a brush, thus it can be
applied easily. It will become stiff again when left alone. In this sense
it is thixotropic (stiff when in rest, fluid when worked). Dextrine dries
more or less "lacquer-like". Most dextrines contain preservatives like
formaldehyde and such. Lesser qualities contain chalk or other fillers to
make it cheaper. This chalky stuff dries to a white gouache-like layer and
has in its own a tremendous "tooth". One could think that when a finger
will be drawn across this type of dry dextrine swiftly and with some
pressure the skin will start to bleed (this does not really happen though).
I still have some of this stuff which in Holland is called "kantoor
lijmpasta" - office glue paste. Apply to me directly if needed, will be
back in Amsterdam after august 20. (Enjoying my holidays in France now,
beware the place is called "Bully"!)
Bas
Jonge Eland papierrestauratie
eland@knoware.nl
t +31 20 623 79 89
f +31 20 627 32 23
VeRes (Dutch Association of Professional Restorers)
postbus 11503
1001 GM Amsterdam
PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER