Re: Oil Printing

Bas van Velzen (eland@knoware.nl)
Wed, 3 Jul 1996 09:15:06 +0100

>Yes, you should use a little chrome alum in the gelatin for oil printing and
>you
>should even try a small amount of dextrin (potato starch, 10% of the gelatin
>amount) to give the gelatin a certain 'tooth' which makes the ink adhear
>better.
>
>The chrome alum is esp. required if you want to use the oil print for
>transfers.
>My favourite formula is:
>
>A
>15% gelatine sol. 160,0 ml
>15% starch sol. (Dextrin) 16,0 ml
>
>B
>6% acetic acid sol. 6,0 ml
>1% chrome alum sol. 8,0 ml
>
>Keep A and B at 60-65 C and slowly add B to A with constant stirring. Take ca.
>40 ml to coat one sheet 50x70 cm. If the gelatin gels in the beaker allready,
>your solution wasn't hot enough. Rewarming is impossible. Beakers and brushes
>are difficult to clean even in hot water after the gelatin has gelled. Let them
>soak in a solution of detergent used for the washing mashine first.
>
>Klaus Pollmeier

KLaus,

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.

Bas van Velzen

Jonge Eland papierrestauratie
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