Paper Conservation: Decisions & Compromises

Study of Phytate Chelating Treatments
Used on Iron Gall Ink Damaged Manuscripts
Véronique Rouchon | Eleonora Pellizzi | Maroussia Duranton
Centre de Recherche sur la Conservation des Collections, Paris, France
Experimentals
Fig. 1 : Aspect of CP solutions prepared at different pH value
Introduction
Many historical documents written with iron gall
inks are endangered by the corrosive effects of
these inks. In this work, a combination of complementary
analytical methods was used for the
first time in order to study the “calcium phytate”
process which is used in conservation studios
to stabilize damaged manuscripts (Neevel 1995).
This process consists of an antioxidant treatment
performed by means of a calcium phytate (CP)
solution, followed by a deacidification treatment
performed with a calcium hydrogencarbonate
(CH) solution. The antioxidant treatment capitalizes
on the properties of myo-inositol hexaphosphoric
acid (phytic acid) that inhibits iron
through chelation. In order to use relatively low
acidic solutions, the pH of the calcium phytate
solution is increased up to values between 5 and
6, which is in the range of the CP precipitation
threshold. This abstract synthesizes a larger work
(Rouchon et al 2011a) that was performed on
laboratory samples in order to investigate how
the calcium phytate precipitate impacts the efficiency
of the treatment.
Preparation of laboratory samples
Samples consisted in Whatman no.1 paper sheets
impregnated with a diluted iron gall ink prepared
with laboratory products 1 .The ink presents
a pH of 3.0 ± 0.1 and the iron content deposited
in the paper (11 mMol·g -1 ) remains inferior but
close to the iron content of original manuscripts
which is usually over 20 mMol·g -1 (Remazeilles et
al 2005).
Before treatment, the samples were artificially
aged for approximately 6 days in a climatic
chamber, using mild ageing conditions (70°C,
65% RH) in order to simulate some degradation
of the paper and to achieve a decay of approx.
10-15% of mechanical properties.
CP solutions were prepared following the protocol
proposed in the nineties (Neevel 1995) and
fully described online (http://irongallink.org). In
order to study the effect of the CP precipitation,
four different values of pH were chosen (Fig. 1):
4.8 (transparent solution), 5.2 (turbid solution),
5.5 (white cloudy solution), and 6 (precipitate
formation at the bottom of the container). The
CH solutions were prepared with a method close
to that used in conservation workshops: 1.1 g of
calcium carbonate was added to 1 L of commercially
available sparkling water 2 . The bottles
were closed immediately after addition, then
left to rest for 24 hours before use. Only the supernatant
was used (pH 5.8 ± 0.2). The various
treatments that were implemented are listed
in Table 1. Each immersion was performed using
2 mL of solution per 1 cm 2 of paper. Afterwards,
the samples were aged again for approx.
2 months in the same conditions as before treatment.
Analytical methods
As conservation treatments in first place aim to
limit physical decay to the paper, mechanical
testing appeared meaningful for the evaluation
of treatment efficiency. The paper mechanical
properties were evaluated with a zero-span
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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