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Calcium Phytate in the Treatment of Corrosion Caused by Iron Gall

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					Calcium Phytate in the Treatment of Corrosion Caused by Iron Gall Inks: Effects on Paper

by LORENA BOTTI, ORIETTA MANTOVANI & DANIELE RUGGIERO

INTRODUCTION: IRON-GALL INK
Iron gall inks1-7, developed later than carbon ink, became steadily more common and widespread
during the Middle Ages. The carbon inks in use up until that time had the invaluable quality of not
being reactive, due to the stability of carbon. They were not subject to chemical alteration and did
not contain any substances that would damage the support. However, carbon inks had two negative
aspects that stimulated the search for new raw materials that could be used in the production of
black ink:
• carbon inks were susceptible to spreading in the presence of humidity;
• they did not penetrate the support deeply and thus could be removed by washing, or even by
simple abrasion.
The latter characteristic often led to parchment manuscripts being erased and written over with new
texts, producing the so-called palimpsests (Note 1).
It seems that the instability of carbon ink may have encouraged the practice of adding small
quantities of ferrous sulphate. Being readily soluble, this salt penetrates the fibres of the support
quite easily and binds the ink more closely to its fibrous structure. However ferrous sulphate
gradually transforms over time into ferrous oxide, producing brownish incrustations and interfering
with the black colour of the carbon ink.
This undesirable browning effect was resolved when it was discovered that ferrous sulphate would
react with tannic acid to produce black particles. Ink makers resorted to adding an extract of gallnut,
containing tannin. A mixture of carbon and iron gall inks was thus obtained, known as "mixed ink",
but it was not long before a further step was taken, i.e. completely eliminating carbon from the com-
position. Beginning in the 11th century iron gall ink became especially popular for legal documents.
Paper also made its appearance in Europe at this time.




Fig. 1: Chemical formula of gallotannic acid (taken from Daniels9)

Production
The artisans that produced iron gall ink followed a common method even though there were some
variations on the various formulas. The procedure began with the extraction of tannic and gallic
acids from gallnuts or other vegetable materials (Note 2). The vegetable material was crushed and
chopped, left to soak in a solvent, such as water or wine, for several days or up to a week, and then
boiled. Occasionally the mixture was boiled without having been left to soak. The cooking stage
usually lasted until the solution was reduced to a third of the initial volume. Ferrous sulphate was
then added to the solution, where it reacted with the gallic acid to produce particles of ferrous
gallate. At this point a thickening agent was added to stabilize the suspension and slow the
precipitation of the particles. The thickening agent gave body to the ink and had the additional
benefit of creating a coating that protected it from excess absorption of atmospheric oxygen,
humectants, anti-fermentation agents and scents could also be added as necessary.

Tannins
There were many definition of tannins based on their properties8-9. These properties included their
astringent taste; their ability to form black, dark brown or green complexes with iron salts; their
ability to form precipitates in gelatine solutions; or their ability to protect animal skins from
spoiling, in the tanning process. All tannins have a polyphenol chemical structure containing
benzene rings, with at least one of these rings being connected to two or more hydroxyl groups.
Tannins are found in diverse concentrations in many plants. Among tannins, gallotannic acid9
(penta-gallolyglucose), also named tannic acid, consists of a molecule of glucose with 5 groups of
gallic acid or di-gallic acid (Fig. 1).
It is now known that the colour of iron gall ink originates from the ferric pyro-gallate complex
obtained by the reaction between ferrous sulphate and gallic acid (3,4,5-trihydroxy-benzoic acid),
which originates in turn from the hydrolysis of gallotannic acid. The raw vegetable materials
contained only small quantities of gallic acid9 but were rich in gallotannic acid, which gradually
produced the gallic acid during the manufacturing process. The procedure of boiling the crushed
galls favoured both the extraction of the gallotannic acid and its hydrolysis into gallic acid. The
addition of acids such as wine, vinegar or hydrochloric acid during the manufacturing process
would clearly have further encouraged hydrolysis.
Leaving the tannin solution exposed to air also promoted hydrolysis. A scum of mould formed on
the surface and produced enzymes that reacted with the glucose of gallotannic acid, causing
hydrolysis into gallic acid. In fact, various recipes recommended, "fermenting the decoction of
gallnuts for at least twelve days".

Additives
Gum arabic was widely used as the thickening agent for the ink. It is a polysac-charide produced in
sap secretions from several species of African acacia trees, particularly the Senegal acacia. Small
incisions in the bark of the trunk are used to stimulate production of the sap.
Examination shows that the recipe books of the "secrets of the art"10 never give the same
proportions of the various components. In addition, the ingredients came from natural sources, with
extremely variable chemical compositions. The vegetable materials varied not only from one
species to the next, but also were dependent on the area in and the stage at which they had been
harvested. For these reasons two batches of ink made from the same recipe, but with raw materials
from different sources, would produce two different final products. These would produce different
results on the writing surface and would behave differently over time.

Ink formation
A number of studies attempted to explain the mechanism for the formation of the ink11-14. In 1994
Wunderlich15 demonstrated that the reaction between gallic acid and iron salts formed a complex
containing equal proportions of Fe3+ and gallic acid. In 1999 Krekel16 proposed the existence of the
following process: gallic acid
Fig. 2: Formation of ferric pyrogallate complex, according to Krekel. The bonds between the Fe
atoms and two of the O atoms in compound (II) are coordination bonds (taken from Neevel35).

first reacts with ferrous sulphate forming ferrous gallate, which is colourless and soluble in water,
and which oxidises easily with atmospheric oxygen to form ferric gallate. The free Fe3+ ions, before
present from the ferrous sulphate, further catalyse the separation of the carboxyl groups of ferrous
gallate to form ferric pyrogallate, a complex that is violet-black in colour and insoluble in water.
The molecular proportions of ferrous sulphate and gallic acid must be 1:1 in order to result in all the
ferrous ions being bound after oxidation is complete. Four molecules of water are incorporated in
the structure of the ferric pyrogallate, bound to the Fe3+ ions. They are positioned perpendicular to
the ions, extending both above and below the structure of the ferric pyrogallate molecule. The
separation of the carboxyl groups leads to the formation of carbonic anhydride, which rises and
accumulates above the surface of the ink in its container, protecting it from further oxidation9, 16, 17
(Fig. 2). The fresh ink is thus not very intense in colour, because it still contains soluble ferrous
gallate that interferes with the violet-black colour of the ferric pyrogallate. It is only after several
days that the action of atmospheric oxygen can complete the oxidation process. This is the reason
why numerous historical recipes recommend ageing the ink in its container for few weeks prior to
use, or recommend the addition of indigo, alizarin or carbon to give a temporary colour that allowed
immediate use of the ink.
From the moment it is used the ink penetrates the interior of the fibrous structure of the paper and
forms the insoluble complex of ferric pyrogallate, which deposits on the surface of the fibres.
Thanks to this mechanism, iron gall ink differs from carbon ink, in that it cannot be easily removed.

Ferrous sulphate
The reaction also forms sulphuric acid through the reaction of the H+ and sulphate ions, which in
turn causes acid hydrolysis of the cellulose18,19?20 in the paper support, with resulting rupture of the
cellulose chains and formation of reducing sugars.
Researchers have examined over 100 ink recipes from the 15th to the 19th centuries, calculating the
relationship between the weight of ferrous sulphate and gallnuts. They found that the typical value
was a ratio of about 5.5:121, which represents an excess of ferrous sulphate. An ink with such an
excess will first produce a black script, but the transformation of ferrous sulphate in the presence of
atmospheric oxygen will gradually transform it into a brown colour, and finally result in the
production of iron oxides. The process is very slow and can take as long as a century.
The excess of ferrous sulphate means that there is an excess of Fe2+ ions. These are harmful, since
they function as catalysts for the oxidative degradation of cellulose9, 19, 20, 22-30. These are radical
reactions, such as the Fenton reaction21,31-34 (Note 3). The Fe2+ ions are oxidised by atmospheric
oxygen and become catalyti-cally inactive Fe3+ ions, but they are continually restored to the Fe2+
state by reducing substances present in the ink and paper (itself usually produced by acid hydrolysis
of cellulose). Chemical analysis of damaged manuscripts shows significant percentages of Fe2+ ions
in the ink relative to the total amount of iron present.
As noted, the interaction of the iron salts, tannic and gallic acids produces sulphuric acid. Acidity
also results from the presence of sulphuric acid in the ferrous sulphate and from excessive use of
humectants.
Ferrous sulphate, the most important source of bivalent iron, is a light green salt that crystallises
with seven molecules of hydration water. Hydrated ferrous sulphate was also known as "green
vitriol" or "copperas". As well as being mined in its natural state6-3'' it could be produced as a by-
product of processing alum. It was also obtained by atmospheric oxidation of iron pyrites (iron
bisulphate, FeS2)6 and then extracted by being dissolved in water and evaporated. This process also
produced sulphuric acid, which was extracted together with the sulphate. It is not known when iron
pyrites were first used as a source of ferrous sulphate. Historically, sulphuric acid was also called
"spirits of vitriol", because it could be obtained by heating green vitriol to high temperatures.
Copper sulphate was also known as "blue vitriol" or "Cyprus blue". Copper sulphate has long been
a common fungicide in agriculture and is sometimes also found as an ingredient in inks.
Some recipes recommended adding pieces of iron to diminish the acidity of iron gall inks, resulting
in a further increase in the quantity of ferrous sulphate. Sometimes iron filings were sprinkled over
the manuscript.

Ink corrosion
Generally the corrosive action13, 36, 37 of iron gall inks on paper is due to the combined action of the
hydrolysis caused by the sulphuric acid and by the oxidative degradation of cellulose catalysed by
the Fe2+ ions. The corrosive action can reach the point of perforating the document. The acid also
tends to migrate outwards and to the surface of the paper producing "haloing"30 and browning. It
renders the paper fragile and reduces the visibility of the text, due to the reduced contrast between
the ink and the colour of the page. The acid can also migrate to the reverse of the overlying page,
producing a brownish mirror image of the text (Fig. 3). Recent research has shown that the
sulphuric acid (and therefore the sulphur) tends to migrate, while the Fe2+ ions remain in the ink and
its immediate vicinity30.

Chelating agents
In order to block the action of the Fe2+ ions it is possible to resort to chelating agents that form
stable complexes with the ions. EDTA (Ethylene Diamine Tetra Acetate), which is a chelating agent
widely used in analytical chemistry, has not produced satisfactory results: the Fe2+-EDTA complex
can still react with hydrogen peroxide by means of the Fenton process and can also form complexes
with Fe3+ ions, rendering them soluble and exposed to reduction to Fe2+ions21,35,38-40.

Phytic acid
Recent research has shown that phytic acid21,35,38-42 can be an effective chelating agent. Phytic acid
is a natural antioxidant present in seeds. In nature, phytina (a mixture of the calcium, magnesium
and potassium salts of phytic acid) is a significant component of plant tissue, with 60% to 90%
phosphorous content. Cereals, nuts, legumes, spores, vegetable oils and pollens contain up to 5%
phytates. They block the oxidation process of unsatured fats catalysed by iron. Their effectiveness
in blocking oxidation can be seen from the fact that seeds will still germinate after four centuries, if
kept in dry storage.
Phytic acid is a particular phosphor related ester of myo-inositol (my-inositol hexaphosphate: Fig.
4). Five phosphate groups are arranged around the midpoint or 'equator' of the cyclohexane skeleton
and a sixth group is in an axial position. The structure, which resembles the arrangement of the
head, tail and legs of a turtle21 (Fig. 5), is crucial in permitting the anti-oxidising function of the
mole-
Fig. 3: Ink corrosion: Perforation of paper, haloing and migration of acid to the reverse of the
overlying page, producing a brownish mirror image of the text.
Fig. 4: Chemical formula of phytic acid (myo-inositol hexaphosphate).




Fig. 5: Structure of phytic acid: five phosphate groups are arranged around the mid-point or
'equator' of the cyclohexane skeleton and a sixth group is in an axial position. The structure
resembles the arrangement of the head, tail and legs of a turtle.




Fig. 6: Structure of myo- and scyllo-inositol hexaphosphate: all the phos-phate groups are in the
equatorial position.

cule43. The compound44, which has all the phosphate groups in the equatorial position (Fig. 6), is
less effective in blocking the Fenton reaction.
Various salts of phytic acid have been tested (sodium, magnesium, calcium), and all have proven
equally effective. However, in order to be effective, treatment with phytates must always be
followed by a deacidifying treatment. De-acidification is necessary in any case, to protect the ferric
pyrogallate complexes from hydrolysis45.
Phytate treatment and deacidification
It has been noted that a combined treatment with sodium phytate and magnesium carbonate46- 48 can
provoke alkaline decay, due to the elevated pH involved. The high solubility of sodium phytate also
permits it to migrate to the borders of the paper during drying, where it can produce brownish
discolouration.
Treatment with magnesium phytate and magnesium carbonate21,37,47,49-56 can also produce
undesirable side effects. Accelerated ageing tests have demonstrated that ink tends to brown and
paper tends to yellow following such a treatment. The treatment solution (pH of approximately 10)
invests the paper with high alkalinity, which produces the undesired effects. As an explanation,
Krekel has developed a theoretical model in which the ink complex is irreversibly destroyed both in
highly acid and highly alkaline (over ph 8.5) environments, forming brown products in the process.
However, treatment with calcium phytate and successive deacidification with calcium carbonate37,
47, 48, 57-60
              has been found to give a pH that is not too alkaline and which can thus be presumed not to
be harmful. The treatment is carried out in a water-alcohol solution instead of a completely aqueous
solution. This limits the migration of the ink and paper degradation products and the brown haloing
effect that are seen when using completely aqueous solutions. It also permits a more uniform
removal of soluble compounds from the inked areas. The alcohol permits the treatment solution to
better penetrate the fibres, thanks to the lower surface tension of the solution.
In view of the clearly positive results of the calcium phytate treatment, it was decided to evaluate its
impact on paper using chemical, optical, and mechanical tests. The conservation-restoration
community is unanimous in recognising the necessity of evaluating treatments not only on the basis
of their immediate efficiency, but also for their short and long-term effects.

EXPERIMENTAL
Sample preparation
The experiments involved testing the effects of the calcium phytate treatment both on plain paper
and on paper prepared with ink. The plain, i.e. the uninked paper used was 130 g/m2 cotton
cellulose paper with starch, trade name "Italia" and produced by Miliani di Fabriano papermakers.
The paper prepared with iron gall ink was 315 g/m2 cotton cellulose paper with gelatine, trade name
"Es-portazione" also from Miliani di Fabriano papermakers.
The ink was prepared according to a recipe suggested by Neevel21, which consists of dissolving
2.46 g of tannin in 50 ml of deionised water at 50°C, then adding 1.57 g of gum arabic and 2.10 g of
ferreous sulphate heptahydrate. Such an ink corresponds to a 2:1 ratio of gallnut to ferrous sulphate,
which is approximately equal to a 5.5:1 molecular ratio of ferrous sulphate to tannin, and has a pH
of 2.75. The use of samples prepared with modern paper and with ink

Table 1: The samples.
made from pure chemicals can assist in understanding observations of naturally aged documents
and drawings, and help to define appropriate conservation-restoration treatments.
The first step of the phytate treatment was immersion (15 minutes) in a solution of calcium phytate
(Sigma brand, approximately 90% concentration), 0.25% by weight in 1:1 water and alcohol, using
ammonia to bring the pH to 635,60 (Note 4). This was followed by a 30 minute deacidification
treatment using a semi-saturated solution (0.006 N) of calcium carbonate obtained by dissolving 30
grams of salt in 100 litres of deionised water and aerating the solution with carbon dioxide until
clear. Some samples were submitted to accelerated ageing in a climate chamber at 80°C and 65%
relative humidity for 24 days (ISO 5630/3; see Note 5).
Preparation of the samples is summarized in Table 1.

Measurements
The following measurements were carried out on the uninked paper samples:
• Hot-extraction pH (UNI 10177 standard)
• Alkaline reserve (UNI 10183 standard)
• Average viscosimetric degree of polymerization61 (UNI 8282 standard)
• Blue Reflectance factor (whiteness) (UNI 7623 standard)
• Folding endurance (TAPPI T 423 om-89 standard)
• Tensile strength (UNI 6438-1 standard)

Table 2: Measurement results, taken after conditioning the samples for at least 24 hours in an
environment of 23°C and 50% RH.




* The Mark-Houwink equation was used for the viscosimetric measure of the polymerization
degree: [η] = 7,5 x 10-3 x DPv, where [η] indicates the intrinsic viscosity. Intrinsic viscosity has
been determined by means of Martin equation, measuring relative viscosity of in 0.5 M
cuproetilendiammina cellulose solutions by means of Cannon-Fenske viscosimeter. The table
indicates the average of three measurements.
** average of at least 20 measurements,
*** average of at least 12 measurements.




The results are shown in Table 2. Two measurements were carried out on the inked samples: cold-
extract pH and average viscosimetric polymerization degree. The results are shown in Table 3.
CONCLUSION
Following the treatments and ageing, the uninked samples did not show significant changes in pH,
alkaline reserve or whiteness. Folding endurance and tensile strength did not change notably after
neither the phytate-carbonate combined, nor the carbonate treatment, nor after artificial ageing.
Degree of polymerization decreased by approximately 10% in the untreated samples after artificial
ageing, while it remained constant in the treated ones.
In the inked samples, the pH values were higher after treatment and remained higher than in the
untreated ones, even after ageing. DP remained constant after the treatments. Ageing resulted in a
notable decrease (approximately 40%) of the untreated samples, but this effect was much less in the
samples treated with carbonate: 23% and almost unnoticeable in the sample given the combined
phytate-carbonate: 10%.
These results clearly confirm that calcium phytate is effective in inhibiting the acid corrosion of
paper by iron gall inks and they demonstrate that the treatment is innocuous to the paper support.

NOTES
1: Palimpsest
The production of palimpsests was particularly common between the 7th and 12th centuries, when
monasteries reused parchment texts from the classical era to write theological and liturgical texts.
For example, in 1820 a specialist in ancient texts named Cardinal Angelo Maj discovered fragments
of Cicero's "De Republica"in a palimpsest preserved in the Ambrosian Library in Milan.

2: Gallnuts and other tannic substances
Galls or gallnuts are growths that develop on the leaves, young branches, twigs and buds of various
plants in response to insects puncturing or laying eggs on them. Galls occur in various rounded
forms and sizes. The plant reacts by developing a woody tissue around the eggs. Gallnuts contain
varying concentrations of tannin. The most frequently cited are:
• "Aleppo gallnut", also known as "blue gall" or "Turkish gallnut". This gall results from the
puncture produced by Cynips tindoria in the buds of Quercus in-fectoria (family Fagaceae), which
is native to the Near East, Northern Africa and Southern Europe. The female insect punctures the
bud and deposits her eggs, provoking formation of the gall. The eggs eventually produce larvae,
which mature to the adult stage. The galls are very rich in tannin.
• "China gall", is produced by the Aphis chinensis, which punctures the leaves of Rhus semialata
(family Anacardiaceae) native to China and Japan. In this case the aphid punctures the underside of
the leaf and the reaction of the components of the saliva provoke the formation of the gall. The galls
are rich in a tannin which is chemically similar to that of the Aleppo gallnut.
• Gallnuts from Hungary and Istria were also held to be of relatively good quality, whilst the
English gall was considered inferior.
Modern extraction methods have shown that the Aleppo gall contains 53-80% gallotannic acid and
3-11% gallic acid; China gall contains 50%-60% tannic substances; the English gall only 4-36%
gallotannic acid and 0-1.5% gallic acid. It can be seen that the percentages of yield vary even for
single species, depending in part on the stage at which the galls have been harvested.
Other sources of tannic substances are oak wood and bark, chestnut wood and bark, the acorn cups
of some oaks (valonid), pomegranate fruit rind and certain exotic fruits (divi-divi, myrabolan) and
leaves (sumac).

3: Fenton reaction
The Fenton reaction begins from hydrogen peroxide and produces HO• hy-droxyl radicals:

Fe2+ + H2O2 → Fe3++ HO + OH•

Hydrogen peroxide in produced during reduction of the oxygen by the Fe2+ iron ions
Fe2+ + O2 + H+ → Fe3+ + HOO•

Fe2++ HOO + H+ → Fe3+ + H2O2

The hydroxyl radicals are very reactive and prone to easily extract hydrogen atoms from cellulose
with the result of organic R* radical formation. These undergo a chain reaction with the oxygen and
a new molecule of R'H cellulose to form ROOH cellulose hydroperoxide and a new radical R'*:

R• + O2 → ROO•

ROO• + R'H → ROOH + R'•

The removal of hydrogen from the cellulose takes place at the 1-4 ß gluco-sidic bonds between the
glucose units and leads to the breakdown of the bonds, with a subsequent reduction in the degree of
polymerisation. Formation of transverse bonds between the cellulose molecules producing coloured
products may also occur. The transverse bonds between the cellulose chains produce a tighter
structure with less space for the entry of water molecules and formation of hydrogen bonds. For this
reason, areas where the paper has been damaged bv ink are less hydrophilic than intact areas.

4: Ferrous and ferric sulphate, ferric pyrogallate
Natural ferrous sulphate in the hydrated salt state is named "melanterite"6 in some dictionaries of
chemistry, but in historical ink and pigment making recipes it is referred to as "green vitriol" or
"copperas".
Depending on the mining source, ferrous sulphate could contain varying concentrations of other
sulphates; copper, manganese, zinc and aluminium35. Copper (Cu2+) and manganese can contribute,
together with Fe2+, to catalysing the oxidation of cellulose.
Atmospheric oxygen tends to convert natural ferrous sulphate into ferric sulphate, therefore the
mineral also contains Fe3+ ions.
A large part of the iron is fixed as insoluble ferric compounds (tannate, pyrogallate, hydroxide), and
therefore tends to rest in the inked areas. Ferric sulphate, formed by oxidation of ferrous sulphate, is
soluble in water but rapidly forms ferric hydroxide, even under acid conditions such as those found
in the inked areas. Therefore, only the Fe2+ ions can migrate beyond the inked areas. Here they are
halted, since the less acid environment favours their oxidation into Fe3+ ions by atmospheric
oxygen, followed by transformation into ferric hydroxide.
The stability of the ferric pyrogallate complex increases as pH increases, reaching a maximum at
about pH 6. For this reason, ammonia is used to bring the slightly acid calcium phytate to pH 6.
Some of the calcium phytate precipitates at this pH35, 62. The solution becomes slightly milky but
remains effective.

5: Standards
• ISO 5630/3 - 1986. Paper and Board. Accelerated Aging, Part 3: Moist Heat Treatment at 80°C
and 65% RH.
It was decided to protract the ageing time because in our previous experiences we noted that the
standard ageing was too brief to permit adequate detection of results.
• UNI 10177 - 1993. Carta, cartone e paste. Determinazione del pH degli es-tratti acquosi.
• UNI 10183 - 1993. Carta e cartone. Determinazione della riserva alcalina.
• UNI 8282 - 1994. Cellulosa in soluzioni diluite. Determinazione dell'indice della viscositä limite.
Metodo ehe usa una soluzione di cuproetilendiammina
(CED).
• UNI 7623 - 1986. Carta e cartone. Determinazione del fattore di riflettanza diffusa nel blu (grado
di bianco ISO).
• UNI 6438-1 - 1986. Carta e cartone. Determinazione delle proprietä di tra-zione. Metodo a
velocitä costante di applicazione del carico.
• TAPPI T423 om-89 - 1989. Folding Endurance of Paper (Schopper Type Tester).

SUMMARY
Calcium Phytate in the Treatment of Corrosion Caused by Iron Gall Inks: Effects on Paper
Iron gall ink, widely used in the past, is a significant factor in the deterioration of documents and
books conserved in libraries and archives. Numerous studies have been conducted in the past to
determine the mechanism of the formation of the ink and its corrosive action on paper, however it
has only been recently that it has been possible to understand the chemical mechanisms at the root
of these processes. It seems certain that the excess Fe ions in the ink act as catalysts in the oxidation
degradation reactions of cellulose.
The use of phytic acid salts seems to be one of the more interesting systems adapted to combating
this phenomenon, having the positive attribute of "chelating" the Fe2+ and impeding it from
catalysing the oxidation reactions. The scope of the work reported in this article was to evaluate the
effects of the treatment on paper supports. A combined treatment with both calcium phytate and
calcium carbonate seems particularly promising.

Le phytate de calcium dans le traitement de la corrosion causée par les encres galliques : ef fets sur
le papier
L'encre gallique, largement utilisée dans le passé, est un facteur essentiel de deterioration des
documents et des livres conserves dans les bibliothéques et les archives. De nombreuses etudes ont
été menées dans le passé arm de determiner le mécanisme de la formation de l'encre et son action
corrosive sur le papier, cependant ce n'est que récemment qu'il a été possible de com-prendre les
mécanismes chimiques responsables de ces processus. II semble certain que ce sont les ions
excédentaires de Fe + dans l'encre qui agissent comme agents catalysateurs dans la degradation
oxydative de la cellulose.
II semble que l'utilisation de phytates (sels d'acide phytique) est un des procédé les plus intéres-
sants capables de lutter contre ce phénoméne car ils servent ďagents chélateurs pour her les ions Fe
et bloquent ainsi les reactions de catalyse oxydative. L'objet de ľétude rapportée dans cet article
était ďévaluer les effests du traitement sur des supports en papier. Un traitement combine utilisant
du phytate de calcium et du carbonate de calcium semble particuliérement prometteur.

Calciumphytat zur Behandlung von Tintenfraß: Wirkungen auf das Papier
Eisengallustinte, weithin gebraucht in früheren Zeiten, ist ein wesentlicher Faktor bei der Schädi-
gung von Archiv- und Bibliotheksgut. In zahlreichen Untersuchungen wurden die chemischen
Vorgänge der Tintenbildung und ihrer korrodierenden Wirkung auf das Papier untersucht, aber erst
in jüngster Zeit gelang es, ihren Ablauf und ihre Ursachen voll zu verstehen. Es erscheint als
gesichert, daß überschüssige Fe2+ Ionen in der Tinte den oxidativen Abbau der Cellulose kata-
lysieren.
Es hat den Anschein, daß Phytate (Salze der Phytinsäure) als interssantes Mittel gegen diese
Vorgangf eingesetzt werden können. Sie sind in der Lage, Fe2+Tonen komplex zu binden und damit
für die Oxidationskatalyse zu blockieren. Gegenstand der hier referierten Untersuchung die
Wirkung einer Phytatbehandluing auf das Papier Eine kombinierte Behandlung mit Calciumphytat
und Calciumcarbonate schient besonders wirksam zu sein..

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Lorena Botti, Orietta Mantovani, Daniele Ruggiero
Centro di fotoriproduzione legatoria e restauro degli Archivi di Stato
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