Phytate: a Potential Conservation Agent for the Treatment of Ink Corrosion Caused by Irongall Inks
by JOHAN G. NEEVEL
INTRODUCTION
Paper manuscripts and pen drawings made with irongall inks are subject to ink corrosion. This is
the deterioration of the paper support by the ink, leading to a loss of mechanical strength. In some
cases the ink has eaten through the paper. This process usually takes centuries. Fig. 1 shows the
damage caused by an irongall ink on a pen drawing made by the 17th-century Italian painter
Guercino, kept at Teylers Museum, Haarlem, the Netherlands. The first signs of ink corrosion are
the formation of brown edges at the ink regions (Fig. 1) and the appearance of the ink at the verso
side of the paper as brown discoloration. This discoloration may consist of cellulose-oxidation
products or of iron (III) hydroxide, formed by oxidation of iron (II) ions. Changes in relative
humidity during storage enhance diffusion of iron (II) ions out of the ink regions. Offsetting of the
ink to a contact leaf can also be observed. Irongall inks basically were produced by mixing aqueous
solutions of iron (II) sulfate and gallotannin-containing extracts of gallnuts.1 The actual ink is
formed by air oxidation of iron (II) ions to iron (III) ions, which form water-insoluble complexes
with the gallotannins.2 The latter are glucose esters of mono- or digallic acid. Although these
processes predominantly take place after applying the ink to the paper with a pen or a brush, some
ink particles are already formed in the solution, causing its black color. To stabilize these ink
particles and increase their adhesion to the paper, a glue, usually gum arabic, was added. According
to Wunderlich, iron (III) ions form macromolecular 1:1 complexes with gallic acid, having zeolitelike structures.2 The black color of the complex is caused by the reversible transfer of an electron
from gallic acid to the bound iron (III) ion upon absorption of light. To bind all iron after complete
oxidation, the molecular ratio of iron (II) sulfate to gallic acid should be 1:1.
Fig. 1. Ink corrosion (indicated by the arrow) on a 17th-century pen drawing by Guercino (Teylers
Museum)
Most historical recipes, however, contain too much iron(II) sulfate, as will be demonstrated below.
Barrow, Van Gulik and Kersten-Pampiglione collected weight ratios between iron (II) sulfate and
nutgalls of 104 15th- to 19th-century historical recipes1'3. These were converted to the molecular
ratios of iron (II) sulfate and tannin. The distribution of these ratios is shown in Fig. 2. To make this
conversion possible, it was assumed that:
• the tannin content of the nutgalls was 55% by weight4,5
• the molecular weight (M) of the tannin was equal to that of the synthetic tannin
penta(digalloyl)glucose (1701.2)
• the iron (II) sulfate was pure and present as a heptahydrate (M=278)
A recipe given by Canneparius in 1660 for a stable, nonbleaching irongall ink had a molecular ratio
of 3.7. This recipe was also established by Lewis in 1787 and by Schluttig & Neumann in 1890.6 A
similar ratio (3.64) can be calculated from the composition of pure iron(III) tannate, given by the
Merck Index.7 Therefore, the assumptions made are reasonable and can be used to select a
representa-
Fig. 2. Distribution of molecular ratios of iron (Fe) to tannin (TAN) in 104 old ink recipes; dotted
lines indicate the window for the ratio in iron (III) tannate
tive ratio. As can be seen in Fig. 2, the predominant molecular ratio in the recipes has about 50%
more iron than needed for complex formation. Therefore, this ratio (5.5) was chosen in our
investigation.
Due to the presence of reducing substances in the paper, not all iron (II) ions are oxidized to iron
(III) ions; therefore, even centuries after being applied to the paper, old irongall inks still may
contain substantial amounts of iron (II) ions. With Mossbauer spectroscopy, Darbour et al.8
established the relative contribution of iron (II) ions to the total amount of iron in an irongall ink on
a 15th-century manuscript to be about 45—48%. By our measurements with this technique an iron
(II) content of about 20% was estimated for a 18th-century manuscript ink. This manuscript showed
severe damage by ink corrosion. Iron (II) ions can accelerate the oxidative degradation of cellulose
by two processes:
• direct production of organic radicals and their subsequent oxidation
• production of hydrogen peroxide, which is decomposed by iron (II) ions into a hydroxyl radical
and a hydroxide ion
The latter reaction is called the Fenton reaction.9'10 Hydroxyl radicals are mobile and very reactive,
especially when water is present to form hydrogen bonds, as is the case with hydrophilic substrates
like paper. They readily abstract hydrogen from cellulose, leading to the formation of organic
radicals. Due to their reactivity, hydroxyl radicals are generally believed to be the main reactants
responsible for the oxidative degradation of cellulose.11,12 Hydrogen abstraction from the carbon
atoms of the (3-glycosidic bond between the glucose units in a cellulose chain leads to the breaking
of these bonds, resulting in a decrease of the degree of polymerization and finally, a loss of
mechanical strength of the paper.13
The other important degradation process in paper leading to a loss of mechanical strength, is acid
hydrolysis.14 Beside iron, most irongall inks contain much acid. Ink pH values range from 2 to
3.7.15 Ink corrosion therefore, could mainly be caused by acid hydrolysis. Then, deacidification
would be enough to stabilize the threatened paper material. Although it has indeed been
demonstrated that deacidification slows down ink corrosion, it fails to block the process
completely.16 As is the case with corrosion caused by copper ions, deacidification does not suffice
to inhibit ink corrosion.17 On the contrary, in some cases aqueous deacidification treatments have
increased ink corrosion by spreading iron (II) ions through the paper.18 Non-acid irongall inks also
cause ink corrosion.17-19 Even in the presence of acid alum-sizing, lignin-containing papers suffer
less from ink corrosion than lignin-free paper.20,21 EDTA (ethylene diamine tetra acetate) was
shown to stimulate ink corrosion.16 All these observations can only be explained by assuming that a
considerable part of the ink corrosion is caused by the iron (Il)-catalyzed oxidation. Lignin acts as
an antioxidant, slowing down the oxidation of cellulose by intercepting hydroxyl radicals and
forming relatively stable radicals. EDTA increases the solubility of iron (III) ions in water by
complexation. Then they are more easily spread through the paper and can be reduced by the
degradation products from cellulose. Although EDTA also forms a complex with iron (II) ions, this
formation does not block the Fenton reaction, because the octahedral Fe(II)-EDTA complex still has
a possibility to coordinate hydrogen peroxide.22
Phytic acid or myo-inositol hexakisphosphate is one of the few complexing
Fig. 3. Structure of phytic acid or myo-inositol hexakisphosphate; positions of phosphate groups
showing similarity to the positions of legs, tail and head of a turtle23
agents that inhibit the iron (II)-catalyzed formation of hydroxyl radicals from hydrogen peroxide by
blocking its coordination site at the iron (II) ion.22 It is the hexaorthophosphate ester of myo-inositol
or hexahydroxycyclohexane. Its structure in aqueous solution is shown by Fig. 3. Five of the ester
groups are in the equatorial position, while one is in the axial position: these 6 positions resemble
those of respectively the four legs, tail and head of a turtle (Fig. 3).23 The mixed calciummagnesium-potassium salt of phytic acid (phytin) is a major component of plant storage tissues,
comprising about 60-90% of the total seed phosphorus. Most cereals, nuts, legumes, oil seeds,
spores, needles and pollen contain about 1-5% by weight of this compound. It is believed to act as
an antioxidant, blocking the iron-catalyzed oxidation of unsaturated lipids.24,25 It seems quite
successful in this, as some seeds are germinable even after 400 years of storage.
Phytic acid forms complexes over a wide range of pH values (1—12) with a variety of polyvalent
cations in the following decreasing order of stability Cu2+>Zn2+>Ni2+>Co2+>Mn2+>Fe3+>Ca2+ 25.
Iron (III)3- and iron (III)4-phytate complexes are insoluble in water, whereas iron (III) phytate is
soluble. Upon increasing phytate concentration, more iron (III) phytate is formed and more iron
(III) ions dissolve. This should be kept in mind when using phytate in conservation treatments. The
stability constant of iron (III) phytate (log K= 17.63
at pH=6) is smaller than that of the iron (III)-EDTA complex (log K=25.1).26 As the iron (Ill)tannatc complex in irongall ink was not destroyed by EDTA, phytate also is expected not to harm
the irongall ink.16 Phytic acid was used as an oxidation inhibitor in a recipe of a sympathetic
irongall ink for use in greeting cards or confidential documents.27 The colorless ink becomes visible
after heating over a radiator, which proves that the iron (Ill)-tannate complex is still formed in the
presence of phytate. Brown-colored irongall inks are expected to consist mainly of iron (III)
oxyhydroxide or rust. Phytic acid is used as a rust-converting agent for corrosion protection of iron
objects, and the formed iron (III) phytate is colorless.28,29 This conversion only takes place under
acid conditions, causing the iron (III) hydroxides to dissolve. Under neutral conditions the
conversion will not take place; therefore treating brown-colored inks with phytate under neutral
conditions is expected not to cause discoloration.
The production of hydroxyl radicals from hydrogen peroxide is almost completely blocked in molar
phytate-to-iron ratios of 0.25 or more.25 It is believed that its specific antioxidant function is due to
the presence of the equatorial-axial-equatorial sequence in the positions of the phosphate groups
(Fig. 3), because scyllo-inositol hexakisphosphate, having all phosphate groups in equatorial positions, showed less efficient blocking of the Fenton reaction.30 Apart from blocking the Fenton
reaction, phytate also offers protection against oxidation by diminishing the concentration of free
iron (II) ions. It accelerates the air-oxidation of iron (II) ions to iron (III) ions by lowering the redox
potential. The iron (III) ions are firmly bound to phytate and cannot be recycled to iron (II) ions.24
Last but not least, phytate salts act as buffers in the pH 4-9 range. Therefore they could also be used
for the deacidification of the paper materials. Because of their antioxidant function, salts of phytic
acid seem to be promising as conservation agents for the treatment of ink corrosion. The aim of this
research project was to investigate this application by simulating ink corrosion in accelerated aging
tests.
EXPERIMENTAL
Materials
Irongall ink was prepared by mixing 0.785 g of gum arabic (as a solution containing 85.5 g/1),
1.050 g iron (II) sulphate, 7 aq. (Riedel-de Haen) and 1.230 g of tannin (95%, Aldrich) in 25 ml of
distilled water. This resulted in a molar ratio Fe:TAN=5.5:l, representative for the ratio occurring in
historical ink recipes, as was demonstrated before (Fig. 2). The pH of the ink had a value of 2.75.
To avoid clogging of the plotter-pen, the ink solution was filtered through a plug of
cotton-wool, when filling the pen. Test sheets for simulation of ink corrosion were prepared with
this ink by plotting five longitudal screen patterns (about 35 mm wide) on to A4-size sheets made of
unsized, lignin-free sulf ite-bleached softwood cellulose (SSC) paper, using a computer plotter
(Hewlett Packard7475A) fitted with a 0.5-mm pen. To prevent directional preference, the screen
patterns were applied diagonally to the machine direction of the paper. Additionally, each sheet was
provided with 6 round ink spots, 8 mm in diameter for surface-pH measurements. The test sheets
were cut into halves in the cross direction. For comparison, one half was kept as a reference, while
the other half was treated with one of the two treatments described below. Also a set of sheets was
prepared with both halves treated differently.
Conservation treatments
During the first days after application the ink usually darkens due to air oxidation.31 To ensure a
similar oxidation state of the ink on all test sheets, they were pre-aged during 3 days in an oven at
70°C and 50% relative humidity (RH). One set of pre-aged half sheets was treated by floating them
during half an hour in an aqueous solution of magnesium bicarbonate (about 0.4% by weight). This
solution was prepared by mixing 10.0 g basic magnesium carbonate ((MgCO3)4 • Mg(OH)2 -5H2O)
with 2.5 liters of distilled water and converting this compound into the bicarbonate by dissolving
carbon dioxide until the pH had changed from 10.15 to 8.15. Not all magnesium carbonate had
dissolved. The comparative set of pre-aged half sheets was treated first by 15 min of immersion in
an aqueous solution of sodium phytate (0.25% by weight). This solution was prepared by dissolving
5.0 g dodecasodium phytate (Sigma) in 2.5 liters of distilled water. As previous accelerated aging
experiments had shown the negative effects of too high pH values (> 10.5) on the mechanical
strength of paper, as well as on the ink color, the pH of the phytate solution was adjusted from its
initial value of 10.6 to 7.9 by dissolving carbon dioxide. Immediately after the phytate treatment the
set was treated by a 30 min immersion in the magnesium bicarbonate solution. All treated sheets
were laid flat on grids to dry. By applying the same deacidification treatment to the comparative
sets, differences in pH could be ruled out as cause of potential differences in aging characteristics.
Aging experiments
The treated test sheets and the reference test sheets were aged in a programmable circulating oven
(Heraeus HC0020) at 90°C and a cycling relative humidity (RH). The loose sheets were suspended
on a grid, permitting free air-flow around them.
Each 3 h the RH was cycled between 80% and 35%. A cycling RH was chosen instead of a fixed
RH, because it was believed that the changing RH would cause iron (II) ions to diffuse out of the
ink regions, creating ink bleeding, a typical sign of ink corrosion. Previous aging experiments
carried out at 90°C and a fixed RH of 50% had not caused ink bleeding. Aging periods were chosen
at 3 day intervals with a maximum of 18 days. Each aging period started with a wet cycle and ended
with a dry cycle. The physical properties of a paper sample depend on whether the sample was
brought from a higher or a lower RH.32 To take account of the hysteresis effect of the moisture
content, the unaged sheets were dried during 2 h at 40°C and 25% RH and conditioned by keeping
them during at least 24 hours at 23± 1°C and 50±2% RH, according to NEN 1108.33 The aged
sheets had already been at a lower RH and were preconditioned by keeping them at 23°C and 50%
RH during at least 24 h before mechanical testing, which was done under the same conditions.
Mechanical testing and pH measurements
The bursting strength of each half sheet was determined tenfold at the screen patterns with a
bursting tester (Adamel-Lhomargy CN.05), according to NEN 1765.34 Thus, for each ageing period
and treatment, 20 values were obtained. The average values with their 95% confidence limits were
calculated and plotted against the ageing periods. The graph data were fitted with exponential
curvesa according to the least-squares method, using relative-error dependent weighing factors.
Surface pH values of the unaged and several aged sheets were determined at the ink spots, as well
as at the blank paper. The paper was wetted with 0.1 — 0.2 ml of distilled water (pH 6.5 - 7) and the
pH values were read 2 min after applying the surface electrode (Schott Gerate N39A, Consort P514
digital pH meter), according to the method described by Kelly.37
RESULTS AND DISCUSSION Observations during the treatments
Upon treatment with the phytate solution, the black irongall ink did not change color. In a separate
test, no color changes and only a slight lightening were observed even after 1 month's exposure to a
0.25% aqueous phytate solution. A
a
Exponential function used: P=AXexp (—BXt)+C; P=bursting strength, t=aging period; A, B and
C are constants
brown ink was simulated by plotting an aqueous iron (II)-ammonium sulphate solution onto a sheet
of paper. Upon oxidation, the brown color developed. This ink did not change color upon treatment
with the phytate solution. The treatment with the magnesium bicarbonate solution, however, caused
a brown discoloration of the black ink. Similar discoloration of irongall ink upon treatment with
magnesium bicarbonate was observed previously.18'36 They could be caused by the high pH values
reached upon treatment. Values up to pH= 10 were measured at the surface of the ink spots (Fig. 6).
Alkaline conditions accelerate the air-oxidation of iron (II) ions to brown-colored iron (III)
hydroxides. Also, under alkaline conditions the tannic acid in the ink can be thermally or
photochemically oxidized to colorless products, causing bleaching of the ink.37 Therefore, the
occurrence of such high pH values should be prevented when treating irongall ink.
During the magnesium-bicarbonate treatment of the phytate-treated samples, a slight precipitate
formed. This precipitate was suspected to be pentamagnesium phytate, which is insoluble in
water.38 The precipitate was washed 3 times with water and left to settle after each washing. It could
be dissolved in hydrochloric acid (about 1 mol/1) and the pH was adjusted to 3.5 with sodium
carbonate. Some drops of the solution were applied to a filter paper, sprayed with a solution of
potassium thiocyanate (about 0.4 g/1) and, after drying, with a solution of iron (III) nitrate (about 1
g/1). Presumably, because of the formation of iron (III) phytate, these spots stayed white, while the
rest of the paper was coloured red by the iron (III)-thiocyanate complex.29 Being less stable than
iron (III) phytate, iron (III) thiocyanate could not form in the presence of phytate. The thiocyanate
test thus indicated the presence of phytate in the precipitate. It is expected that magnesium phytate
was also formed inside the treated paper samples. As phytate salts are efficient pH buffers,
magnesium phytate could act as an alkaline reserve against acid contamination.26
Aging and mechanical testing
Unaged samples burst randomly, while reference samples already showed bursting along the ink
lines after 3 days of aging, indicative of ink corrosion. After 12 days of aging, some bursting at the
ink lines could be observed with the treated samples, especially the ones treated solely with
magnesium bicarbonate. Fig. 4 shows some examples of treated samples after 15 days of aging and
after the bursting test. As can be seen, bursting along the ink lines has taken place in the sample
treated with magnesium bicarbonate, while the other sample, treated with phytate and magnesium
bicarbonate, shows random bursting. This difference in bursting behavior indicates an effective
inhibition of ink corrosion through the
Fig. 4. Samples, aged for 15 days, after bursting test; top sample: treated solely with magnesium
bicarbonate, bottom sample: treated with phytate and magnesium bicarbonate
combined treatment. Phytate-magnesium-bicarbonate-treated samples aged for 18 days showed
relatively more bursting at the ink lines than samples aged for 15 days, indicating some ink
corrosion was still occurring. The ink dots on the reference samples showed some bleeding after 18
days of aging.
In Fig. 5 the average values of the bursting strengths of the reference and the treated samples are
plotted against their period of aging. The error bars indicate the 95% confidence limits (some were
smaller than the dimensions of the points and could not be shown). To compare, results of a
previous aging experiment with reference samples, conducted at a constant RH of 50% are
incorporated. The reference samples had lost their mechanical strength very fast: within 5.6±1.0
days of aging their bursting strength had halved. As can be seen from the starting points of the
curves, both treatments have increased the initial bursting strength by about 11-14%. This is not
uncommon for aqueous treatments, as water 'relaxes' the paper and increases its elasticity.32
As can be seen in Fig. 5, the bursting strengths of the treated samples show a similar behavior: until
9 days of aging the strength decreased very little, while after 9 days the bursting strength decreased
faster. This behavior can be explained
by the effect of cross-linking, leading to a temporary increase in wet breaking strength during the
first 9 days of aging.39 Therefore, the first part of each curve (0—9 days) has been fitted with an
exponential function, different from the last part (9-18 days). Because of the higher degradation
rate, the aging curve of the reference sample showed only a small influence from cross-linking. This
caused a maximum deviation from a true exponential function at 3 days of aging. With the treated
samples the maximum deviation from an exponential curve took place at about 9 days, therefore
both treatments seem to have slowed down cross-linking.
The treatment with magnesium bicarbonate (M) improved the stability of the paper samples: a halfvalue period of 15±1 days of aging was calculated for the bursting strength. Therefore,
deacidification slows down ink corrosion. The combined treatment with phytate and magnesium
bicarbonate (Ph+M) provided the best protection against ink corrosion. By extrapolating the
exponential aging
Fig. 5. Effect of different treatments on bursting strength (P) of SSC paper aged at 90°C and RH
cycling between 80% and 35%; Ref.: reference, Ph: phytate treatment, M: magn. bicarb, treatment;
50% RH: aged at a constant RH of 50%
Fig. 6. Effects of aging and treatments on surface-pH values of ink and papers of SSC paper
samples; Ref.: reference, Ph: phytate-treated, M: magn. bicarb.-treated
curve of these samples, shown in Fig. 5, a half-value period for the bursting strength of 23±1 days
was calculated.
In Fig. 6 some values of the surface-pH measured at the ink spots and at the blank paper are
presented. As can be observed, the treatments cause high pH values of 9.4-9.5 at the ink surface.
The adverse effects of high pH values have been discussed before. Upon aging, pH values dropped
rapidly, especially during the first days: after 3 days of aging the ink had a pH of about 6.8—7.0 on
both treated sets (M and Ph+M), after 12 days of aging the pH of the ink had dropped to about 4.34.7. The latter values did not change upon further aging. Both treated sets showed similar pH
values. Therefore, their different degradation rates cannot be due to pH differences. A higher pH
value would have slowed down oxidation, too.13'40 As this is not the case, the difference in
deterioration rates can only be explained by the antioxidant function of phytate. Previous aging
experiments were conducted at 90°C and a constant RH of 50% on paper samples written with the
same ink (results not shown here). A single treatment with an aqueous solution of sodium phytate
(0.25%, pH=7.9) during half an hour led to an increase of the half-life for the initial bursting
strength from 7.0±1.4 days for the reference samples to 40±5 days for the treated samples.
Therefore,
to protect the paper against ink corrosion, the extra deacidification treatment might not be needed.
Reference samples aged at 90°C and a constant RH of 50% (Fig. 5, second lowest curve)
deteriorated slower than the samples aged at a cycling humidity (Fig. 5, lowest curve). At 50% RH
it took an aging period of 7.0± 1.4 days for the bursting strength to be halved; the period needed to
reach this with cycling RH was 5.6±1 days. A changing RH could cause more deterioration due to
increased oxidation.41 Changing from dry to moist aging causes the formation of radicals, as has
been shown by the technique of chemiluminescence.42 Besides the increased mechanical
deterioration increased yellowing of the paper was observed, especially when treated paper samples
were compared. Aqueous treatments increase the accessibility of the paper, while the presence of
alkaline materials can, in the course of artificial aging, lead to yellowing of cellulose through the
formation of brown products.43'44 With the treated samples, wetting by a drop of water produced a
brown edge at the wet-dry interface, caused by the migration of degradation products. At places
where sodium phytate had accumulated during the drying on grids of the treated samples, brown
stains had developed during accelerated ageing. These could be caused by the increased alkalinity
or by a dehydration process on the cellulose fibres, induced by the salt.45 Formation of these stains
could be prevented by changing from sodium to magnesium phytate. The latter compound is less
soluble and will not migrate.
CONCLUSIONS AND FUTURE RESEARCH
Most ancient irongall inks contain too much iron, partly present as iron (II) ions. These iron (II)
ions catalyze the oxidation of cellulose by producing hydroxyl radicals from hydrogen peroxide (the
Fenton reaction). This oxidation can lead to a loss of mechanical strength of the paper: ink
corrosion. Ink corrosion can also be caused by the acid present in the ink, leading to acid hydrolysis.
Changes in relative humidity during storage cause the iron (II) ions to diffuse out of the ink regions.
By air-oxidation iron (III) hydroxides are formed, which are visible as brown ink bleedings,
characteristic of ink corrosion. Ink corrosion is accelerated by a cycling relative humidity.
Treatment of endangered paper samples with an aqueous solution of the complexing agent phytate
leads to a remarkable protection of the paper against ink corrosion. In the iron (II)-phytate complex
the coordinating position for hydrogen peroxide is blocked by phytate, and therefore the Fenton
reaction is inhibited. No discoloration of the ink was observed upon treatment with an aqueous
solution of sodium phytate. Therefore, salts of phytic
acid are promising agents for the conservation treatment of ink corrosion on paper manuscripts and
pen drawings. Further research will focus on the eventual adverse effects of phytate on brown iron
oxyhydroxide-containing inks, the prevention of the brown stains by changing the phytate salt, the
development of a nonaqueous treatment with phytate and the comparison of the effects of a phytate
treatment with those of other agents, such as ammonium caseinate. The latter has also been shown
to provide protection of paper against ink corrosion, possibly based on complexation of iron ions.
ACKNOWLEDGEMENTS
This work was performed at the Central Research Laboratory for Objects of Art and Science in
Amsterdam. The financial support was donated by the Dutch Ministry of Education, Culture and
Science as part of the research programme 'Verzuring Cultuurgoederen'.a I would like to thank
everybody who has provided information or practical help to make this article possible, especially
Sjack Elings of the Delft University of Technology for providing the idea of using phytic acid as an
antioxidant and A. M. van der Kraan of the Delft University of Technology for conducting the
Mossbauer-spectroscopic measurements. My special thanks arc also due to Robien van Gulik of
Teylers Museum in Haarlem and Walter Castelijns of the Rotterdam Municipal Archives for
introducing me into the paper-restoration practice, as well as to Henk Porck and Sophia Pauk of the
Royal Library in The Hague and Judith Hofenk de Graaff of the Central Research Laboratory for
Objects of Art and Science in Amsterdam for their useful contribution in the discussions. Last but
not least I want to thank John Havermans of TNO Centre for Paper and Board Research in Delft for
providing useful information, and for allowing me to use test samples of their ink-corrosion study.21
SUMMARIES
Phytate: a Potential Conservation Agent for the Treatment of Ink Corrosion Caused by Irongall
Inks
Ink corrosion, the degradation of paper by irongall inks, destroys paper manuscripts and pen
drawings. The degradation can be attributed to both acid hydrolysis and iron (II)-catalyzed
oxidation of cellulose.
a
A Dutch translation of the article will be published in De Restaurator.
Phytic acid, a natural antioxidant, blocks the latter process. Its action has been investigated by
simulating ink corrosion with accelerated aging tests at 90°C and a relative humidity, cycling each 3
hours between 35% and 80%. Mechanical strength was tested with a bursting tester at screen
patterns, made with an irongall ink of a composition representative of old ink recipes. When ink
corrosion occurred, the aged paper samples burst at the patterns. By deacidification with an aqueous
solution of magnesium bicarbonate, the half-life of the bursting strength increased from 6 to 15
days. In combination with a treatment with an aqueous solution of sodium phytate, the half-life
increased to 23 days. Surface pH values of both treated sets were similar. Therefore, the increase in
stability must be due to the antioxidant function of phytate. Further research should lead to practical
phytate-based conservation treatments of manuscripts and pen drawings threatened by ink
corrosion.
Phytate: un agent de conservation potmtiel pour le traitement de la corrosion causee par I'encre
ferro-gallique
L'encre ferro-gallique detruit les manuscrits ainsi que les dessins a la plume. Deux mecanismes sont
possibles: l'hydrolyse acide de la cellulose et l'oxidation catalysee par l'ion ferreux. L'acide
phytique, un anti-oxydant naturel, bloque ce dernier mecanisme. La corrosion a ete simulee par
vieillissement accelere a 90°C et une humidite relative entre 35 et 80% changee toutes les 3 heures.
La resistance mecanique a ete testee par mesure de la resistance a l'eclatement d'un quadrillage
dessine a l'aide d'une encre ferro-gallique d'une composition representative des recettes anciennes.
En cas de corrosion, les echantillons de papier vieilli se dechiraient le long de ce quadrillage. Apres
une desacidification aqueuse avec du bicarbonate de magnesium, la demi-vie de la resistance a
l'eclatement passe de 6 a 15 jours. En combinaison avec un traitement avec une solution aqueuse de
phytate de sodium, cette periode passe a 23 jours. Les valeurs de pH de surface des deux series
traitees sont similaires. Pour cette raison, l'augmentation de stabilite doit etre due a la fonction antioxydante du sel de l'acide phytique. Des recherches futures devraient permettre de developper des
traitements de conservation de manuscrits et de dessins a la plume menaces par la corrosion causee
par l'encre ferro-gallique.
Phytate: Potentielle Wirkstqffe zur Konseroierung Tintenfraß-gefährdeter Manuskripte und
Zeichnungen
Manuskripte und Federzeichnungen bei denen Eisengallustinten verwendet wurden, werden zersetzt
durch Tintenfraß. Dieser Zersetzung liegen zwei Mechanismen zugrunde: saure Hydrolyse und
durch Eisen(II)-Ionen katalysierte Oxydation der Zellulose. Phytinsäure, ein natürliches
Antioxydant, blockiert letzteren Mechanismus. Ihre Wirksamkeit wurde untersucht durch
Simulation des Tintenfraßes anhand künstlicher Alterung bei 90°C und einer zyklisch zwischen 35
und 80% variierten relativen Luftfeuchte. Der Berstwiderstand des Papiers wurde mittels eines
Tintenrasters getestet, bei dem Eisengallustinte in einer für alte Tinten repräsentativen
Zusammensetzung verwendet wurde. Bei Auftreten von Tintenfraß rissen die gealterten
Papierproben entlang der Streifenstruktur. Durch Entsäuerung mit Magnesiumbi-carbonat nahm die
Halbwertzeit des Berstwiderstandes von 6 auf 15 Tage zu. Die zusätzliche Behand-lung mit einer
Natriumphytat-Lösung erhöhte die Halbwertzeit auf 23 Tage. Da der Oberflächen-pH-Wert der
behandelten Proben vergleichbar war, wird die Stabilitätsverbesserung der antioxydierenden
Wirkung des Phytats zugeschrieben. Die Entwicklung von Konservierungsmethoden fur von
Tintenfraß gefährdeten Manuskripten und Zeichnungen auf der Basis von Phytaten ist Gegenstand
weiterer Unter-suchungen.
REFERENCES
1. Barrow, W J.: Manuscripts and documents, their deterioration and restoration. Charlottesville:
University of Virginia Press, 1955, Table 1.
2. Wunderlich, C.-H.: Geschichte und Chemie der Eisengallustinte. Restauro 100 (1994): 414-21.
3. Van Gulik, R. & Kersten-Pampiglione, N.: Recipes iron gall ink. Unpublished results.
4. Schweppe, H.: Handbuch der Naturfarbstoffe: Vorkommen, Verwendung, Nachweis.
Landsberg/Lech: Ecom-ed, 1993: 469-73.
5. Flieder, F., Barroso, R. & Oruezabal, C: Analyse des Tannins Hydrolysabk Susceptibles d'entrer
dans la Composition des Encres Ferro-Gallique. Preprints of the 4th Triennal Meeting, Venice. Los
Angeles: ICOM Committee for Conservation, 1975: 75/15/12, 1-16.
6. Talbot, R., LeClerc, F. & Flieder, F.: La Deterioration des Encres Mitalh-Galliques et Leur
Regeneration Chimique. In: Les Documents Graphiques et Photographiques: Analyse et
Conservation. Paris: Centre National de la Recherche Scientifique, 1981: 41-70.
7. An: The Merck index. 11th edn. Rahway, NJ: Merck & Co., Inc., 1989: Tannic Acid: No. 9023,
Ferric Tannate: No. 3981.
8. Darbour, M., Bonnassies, S. & Flieder, F: Les Encres Metallogalliques: Etude de la
Degradation de I'Acide Gallique et Analyse du Complex Ferrogallique. Preprints of the 6th
Triennal Meeting, Ottawa, Vol. III., Los Angeles: ICOM Committee for Conservation, 1981:
81/14/3, 1-14.
9. Walling, C: Fenton's reagent revisited. Accounts of Chemical Research 8 (1975): 125-31.
10. Croft, S., Gilbert, B. C, Lindsay Smith, J. R. & Whitwood, A. C: An E.S.R. investigtion of the
reactive intermediate generated in the reaction between Fe" and H2O2 in aqueous solution. Direct
evidence for the formation of the hydroxyl radical. Free Radical Research Communications 17
(1992): 21-39.
11. Emery, J. A. & Schroeder, H. A.: Iron-catalyzed oxidation of wood carbohydrates. Wood
Science and Technology (1974): 123-37.
12. Veness, R. G. & Evans, C. S.: Products of oxidation of cellulose by hydrogen peroxide during
fungal degradation. In: Kennedy, J. F, Phillips, G. O. & Williams, P. A., eds. Cellulosics: pulp,
fibre and environmental aspects. New York: Horwood, 1993: 451-6.
13. Shahani, C. J. & Hengemihle, F. H.: The influence of copper and iron on the permanence of
paper. In: Needles, H. L. & Zeronian, S. H., ed. Historic textik and paper materials. Advances in
Chemistry Series, 212. Washington, D.C.: American Chemical Society, 1986: 387 419.
14. Van der Reyden, D.: Recent scientific research in paper conservation. Journal of the American
Institute for Conservation 31 (1992): 117-38.
15. Sistach, M. C. & Espedaler, I.: Organic and inorganic components of iron gall inks, Preprints
of the 10th Triennal Meeting, Washington D.C., II. Los Angeles: ICOM Committee for
Conservation, 1993: 485-90.
16. Porck, H. J. & Castelijns, W: A study of the effects of iron and copper on the degradation of
paper and evaluation of different conservation treatments, Preprints IADA Congress 1991,
Uppsala. Marburg: Internationale Arbeitsgemeinschaft der Archiv-, Bibliotheks- und
Graphikrestauratoren, 1991: 1-7.
17. Banik G., Stachelberger, H. & Messner, K. Ontersuchungen der destruktiven Wirkung von
Tinten auf Schrifttragermaterialien. Restauro 94 (1988): 302-8.
18. Hey, M.: The deacidification and stabilisation qfirongall inks. Restaurator 1-2 (1981): 24—44.
19. Heller, F., Mairinger, E, Schreiner, M. & Wächter, O.: Tintenftaß im Papier. Restauro 99
(1993): 115-21.
20. Brecht, W. & Liebert, E.: Der Einfluß von Schreibtinten auf die Festigkeit von Papieren. Der
Papier Fabrik-ant - Wochenblatt fur Papierfabrikation 9 (1943): 330-4.
21. Berkhout, S. A. & Havermans, J. B. G. A.: Simulatie en identificatie von inktvraat in papier,
veroorzaakt door ijzergalinkten. De Restaurator 24 (1994): 5-12.
22. Graf, E., Mahoney, J. R., Bryant, R. G. & Eaton, J. W.: Iron-catalyzed hydroxy I radical
formation. The Journal of Biological Chemistry 259 (1984): 3620-4.
23. Agranoff, B. W: //. Biochemical mechanisms in the phosphatidylinositol effect. life Sciences 32
(1983): 2047-54.
24. Graf, E., Empson, K. L. & Eaton, J. W.: Phytic acid - a natural antioxidant. The Journal of
Biological Chemistry 262 (1987): 11647-50.
25. Graf, E. & Eaton, J. W: Antioxidant junctions of phytic acid. Free Radical Biology & Medicine
8 (1990): 61-9.
26. An.: Phytic acid - natural substance (Technical Bulletin). Tokyo: Mitsui Toatsu Chemicals,
Inc.
27. Morimi, K.: Colorless inks and pens containing the inks. Japanese Kokai Tokkyo KohoJP
58,152,071, 1983 (Chemical Abstract: 100 (1984): 87452d).
28. Graf, E.: Applications of phytic acid. Journal of the American Oil Chemists' Society 60 (1983):
1861 7.
29. Oberleas, D. & Harland, B. F.: Analytical methods for phytate. In: Graf, E., ed. Phytic acid chemistry and applications. Minneapolis: Pillsburg Company, 1986: 77—100.
30. Hawkins, P. T, Poyner, D. R., Jackson, T. R., Letcher, A. J., Lander, D. A. & Irvine, R. F:
Inhibition of iron-catalysed hydroxyl radical formation by inositol polyphosphates: a possible
physiological function for myo-inositol hexakisphosphate. Biochemical Journal 294 (1993): 929-34.
31. Waters, C. E.: Inks. Circular of the National Bureau of Standards C426 (1940): 22-24.
32. Dwan, A.: Paper complexity and the interpretation of conservation research. Journal of the
American Institute for Conservation 26 (1987): 1-18.
33. An.: Papier en karton; Algemene onderzoeksvoorwaarden en conditioneren van monsters.
Nederlandse Norm NEN 1108, 4th edn. Delft: Nederlands Normalisatie Instituut, 1982 (similar to
ISO 187: 1990).
34. An: Papier en karton; Bepaling van de berststerkte (meetbereik 70-1100 kPa): Nederlandse
Norm NEN 1765, 4th edn. Delft: Nederlands Normalisatie Instituut, 1984 (similar to ISO 2758:
1983).
35. Kelly, G. B.: Practical aspects of deacidification. Journal of the American Institute for
Conservation 13 (1972): 16-28.
36. Lienardy, A. & Van Damme, P.: Effet de la desaddification sur I'encre ferro-gallique. Studies
in Conservation 36 (1991): 155-9.
37. Clapp, P. A., Du, N. & Evans, D. F: Thermal and photochemical production of hydrogen
peroxide from dioxygen and tannic acid, gallic acid and other related compounds in aqueous
solution. Journal of the Chemical Society, Faraday Transactions 86 (1990): 2587-92.
38. Nolan, K. B., Duffin, P. A. & McWeeney, D. J.: Effects of Phytate on Mineral Bioavailability.
In Vitro Studies on Mg2*, Ca2+, Fe2+, Cu2+ and Zn2+ (also Cd2+) Solubilities in the Presence of
Phytate. Journal of the Science of Food and Agriculture 40 (1987): 79-85.
39. Graminski, E. L., Parks, E. J. & Toth, E. E.: The effects of temperature and moisture on the
accelerated aging of paper. In. Eby, R. K. ed. Durability of macromolecular materials. Advances in
Chemistry Series, 95. Washington, D.C.: American Chemical Society, 1979: 341-55.
40. Arney, J. S. & Novak, C. L.: Accelerated aging of paper - the influence of acidify on the
relative contributon of oxygen-independent and oxygen-dependent processes. Tappi 65 (1982): 1135.
41. Shahani, C. J., Hengemihle, F. H. & Weberg, N.: The effect of variations in relative
humidity on the
accelerated aging of paper. In: Zeronian, S. H. & Needles, H. L. eds. Historic Textile and Paper
Materials II. Advances in Chemistry Series, 410. Washington, D.C.: American Chemical Society,
1989: 63-80.
42. Kelly, G. B., Williams, J. C, Mendenhall, G. D. & Ogle, C. A.: The use of chemiluminescence
in the study of paper permanence. In: Eby, R. K. ed. Durability ofmacromolecular materials.
Advances in Chemistry Series, 95. Washington, D.C.: American Chemical Society, 1979: 117-25.
43. Roudier, A. & Saulquin-Bisson, A.: Recherches sur lejaunissement des pates cellulosiques et
des papiers, I"c partie. Bulletin de l'Association Technique de l'lndustrie Papetiere (1959): 109-22.
44. Roudier, A. & Sauret, G.: Recherches sur lejaunissement des pates cellulosiques et des papiers,
2CTnc partie. Bulletin de l'Association Technique de l'lndustrie Papetiere (1959): 187-98.
45. Hey, M.: The washing and aqueous deacidtfication of paper. The Paper Conservator 4 (1979):
66-80.
Johan G. Neevel
Centraal Laboratorium
Gabriel Metsustraat 8
NL-1071 EA Amsterdam
The Netherlands