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Washing Watercolours



I am restoring/rebinding a 1818 edition of "Culpeper's Herbal", which was in
poor external condition - the boards were missing - the inner leaves were
reasonably clean, except for the title signature and marginal soiling.     All
the  text leaves have been washed and deacidified.     Oversewn in groups were
the forty plates of hand-coloured flower engravings ( some 12 or so  plants per
plate).     The colours used were:  lt and dk green, yellow,  lt & dk blue,
pink, brown, etc.     I would like to wash/deacidify these  plates.      The
paper is heavier than the text leaves, and is lightly but uniformly browned.

As a trial to check loss of colour I have tested a solution of warm alcohol
soluble
nylon (ICI 'Calaton')brushed onto the pigment at ca 2% concentration (see
leaflet
from Picreator Enterprises Ltd, London, ) on the last  plate prior to a wetting
with
alcohol/water mixture and a  bath of saturated calcium hydroxide for
deacidification.     As a result  I noticed a light yellow pigment has leached
through to the back of the  plates from each flower (mainly blue and green
areas) - the colours  from the front appear unaffected, but there is slight
sideways diffusion  of the yellow.     Presumably this pigment is alcohol
soluble.     The nylon coating is not visible to my eye.

Queries.
         Before I go any further is this procedure recommended to fix  the
watercolour, or should I not use the method because of the pigment  migration?

Is a single coat adequate or a stronger solution > 2%? -   Johnson's "The
Thames & Hudson Manual of Bookbinding", p.56,   suggests 5%  -    As  the nylon
is alcohol soluble is it best to place the plates face up  in the deacidifying
solution, with minimal solution allowed to flow onto  the front surface? - I
assume the act of wetting the paper initially as  usual with alcohol/water
mixture may tend to remove the protective  coating and I will just have to
trust the penetration from the plate  reverse is adequate to assist
deacidification?

Instead of the alcohol/water wetting mixture would a pure alcohol solution be
best to remove the soluble contaminants initially (accepting the slight loss of
yellow pigment) and then to brush the deacidifying solution on the back?

Rodney Fry,
Berks,
England.
[rod.fry@gecm.com]


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