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Esperon 1
Emma Esperon
April 17, 2012
Jackie Esposito
L ST 490
The Dark Side of Iron Gall Ink: Corrosion and Conservation
Imagine a world where the drafts of the American Constitution, Leonardo da Vinci’s
notebooks, and ink drawings done by Rembrandt and Van Gogh are piles of corroded
confetti. This would be the reality for many documents written with iron gall ink without
present day preservation and conservation efforts. When evaluating a piece, a conservator
must decide whether to perform no action, preventative conservation, chemical
conservation, or physical mending (Pedersoli). Each of these decisions can be called upon
for different scenarios just as they are all associated with different side effects. Throughout
the process of assessing potential and current damage, conservators offer varying opinions
and preferences about the “correct” way to restore a corroded record. Thus, the
controversy of iron gall inks lies in how to preserve these tender documents through
aqueous, non-‐aqueous, or abstinence from treatments.
Popular from the Middle Ages to the creation of synthetic inks in the 1900s, iron gall
ink is one of the more prevalent inks found in archives today. Iron gall ink gets its name
from the ingredients it is comprised of: tannin (from galls on trees), vitriol (iron sulfate),
gum Arabic (the binding agent), and water. Making preservation more complicated for
librarians, there are hundreds of recipes with varying ingredients. Plus, iron gall ink
cannot simply be identified by its color. The iron in the ink rusts, changing the color and
opacity of the ink when documents are exposed to a moist environment. Transitioning
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from a deep black to a dark brown to a light yellow, with an array of shades in between,
iron gall ink can range from appearing like its blacker predecessor, carbon ink, to lighter
non iron mixes. Carbon ink is often confused with its successor since the high carbon
content level of around 80% generally causes the carbon ink to appear very black like fresh
iron gall ink (Banik). Since inks can be easily confused during visual assessments,
conservationists test the ink for iron content, while still wary of false positives from inks
that were contaminated with iron during the manufacturing process. These components
create hardy, generally non water-‐soluble ink with high acidity and iron levels that can
corrode documents over time.
Once the iron gall ink is confirmed through testing, a visual assessment can be made
on the direness of the preservation. When assessing a document it is important to notate
the original, pretreatment description of the piece and judge based on these characteristics
if treatment will positively impact and preserve the document. Iron gall ink corrodes
records on multiple levels. Vitriol was often overly used in the creation of iron gall ink
leading of an excess of iron sulfate. The sulfate generates acidic compounds that must be
neutralized by an alkaline buffer system and then the remaining iron ions must also be
expelled to prevent rust (Banik). In some instances documents have specific risk indicators
that imply whether a document should receive a specific type of treatment or not. Thus, a
conservator must determine the net gain—if a treatment would destabilize the piece
further or preserve it better.
One risk factor is the depth and surface area of the ink on the page. Iron gall ink is
both acidic and prone to rusting in moist environments (Banik). These qualities cause the
ink to crack while the remainder of the paper can remain sound. If the document is a
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drawing or has areas with large brush marks or insignias, this represents a high-‐risk
section where numerous cracks can form, connect, and leave a hole in the page. When
pages are particularly damaged in this fashion, sometimes a researcher can “read” the holes
in the document based on where the ink used to be. The ink strokes can also be heavy
applied, saturating the page instead of layering a thin deposit on the top layer of the
document. So when the ink cracks it cuts through the entire page and not just the surface
layer of ink. The image below demonstrates the cracking of ink over time and the
importance of preserving records before the fissures prove detrimental to the stability of
the entire piece.
(Banik)
Another common ailment that documents suffer from is “bleeding”. If a document
gets wet, water damaged, or even in a humid environment, excess iron particles can travel
through the moisture and seep into areas of the document immediately surrounding the
text. This causes a discoloration around the words making it appear hazy or shadowed.
Furthermore, ink tends to bleed through the paper in sections of the document that have
water damage. This shows that the ink may still be water-‐soluble and thus aqueous baths
should not be implemented to stave off corrosion. However, if a document does not have
severe water damage or water-‐soluble ink, an aqueous bath could remove the particles that
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contribute to the ink corrosion, deacidify the document, or simultaneously chelate and
deacidify the record depending on the solution implemented.
During the washing process, a document with iron gall ink is soaked into a water
bath for a designated amount of time and temperature. During this process the acidic
partials and some iron(II) ions are dissolved in the water and removed from the document.
This will elongate the life of the document; however, it will not prevent the remaining
particles to decay the record in the future (Reißland 125). While distilled water is
primarily used in this capacity, sometimes conservators utilize tap water so that the
calcium and magnesium salts in the water bond with the iron(II) ions. The process of
“paper simmering” or boiling the documents in 90°-‐95°C water for 15-‐20 minutes was
common practice for approximately 30 years (Tse 14). This process removes 50-‐100% of
the iron(II) ions and most of the acids, making the page appear to be whiter (Banik). Yet,
there can still be catastrophic side effects.
Considering that most documents are made out of fragile paper, boiling the records
does not sound like an intelligent plan. There are negative consequences of simmering
pieces such as the paper has a tendency to shrink in such high temperatures, especially
when it has a cotton base (Banik). Also the water bath is dislodging ions and particles
without any direction of where these particles should go. While many remain in the water
bath after the document is removed, some particles are reabsorbed into the paper causing
bleeding (Reißland). Thus the particles seep into the document around the text, which may
not be immediately evident but can still mar the page overtime. Reißland and de Goot,
esteemed conservators from the Netherlands, claim that the paper washing was the “least
effective in delaying ink corrosion … using distilled water, even if the water temperature
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was adjusted at 90°C” (128). While these side effects are not a new discovery, other
practices such as the calcium phytate treatment were not widely endorsed until after 2001
(Tse 14). This means that documents like the National Archives and Library of Canada’s
McKay Sketchbook were treated with less effective conservation methods and may require
follow up attention in the future.
Another treatment option to protect against corroding iron gall ink is through
deacidification. In an aqueous solution this process introduces a chemical (usually
Magnesium carbonate, Calcium bicarbonate, or Magnesium bicarbonate) that is very basic
(numerically high pH) in order to neutralize the acidity in the ink and prevent future acid
hydrolysis (Banik). While this does protect the paper and preserve the ink for some time,
this procedure does not totally negate the threats of iron gall ink. The second part of the
problem with this type of ink is that it also oxidizes, essentially rusting. The alkaline
compounds do little to prevent the oxidation and only temporarily convert the iron(II) ions
into iron(III) ions by oxidizing them in a highly basic setting, opposed to the previously
acidic setting (Reißland 125). Thus the short lived iron(III) ions are not catalysts for
oxidation like their counterparts and their transformation earn the document a momentary
respite from the iron(II) ions and acid. A byproduct of this seemingly effective process is
that the paper initially appears significantly whiter and then rapidly yellows, especially if
the wash contains magnesium, as shown in the following figure (127-‐128). Furthermore,
the addition of these aqueous compounds sometimes causes the ink to fade, bleed, or wash
out (Banik). These results are so variable because there is not one established way to make
iron gall ink, instead there are a myriad of recipes dating back well before the historically
consulted 1596 A Booke of Secrets.
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(Reißland 128)
In addition to the water-‐based procedure, there is also a non-‐aqueous treatment
that is implemented when the iron gall ink is especially water soluble due to its unique set
of ingredients. However, this treatment similarly deals with the acids and not the iron. An
alkaline compound is evenly sprayed over the pages of the document where it reacts with
the moisture that is already present within the record. Two of the most common alkaline
compounds include: magnesium oxide, commonly called “Bookkeeper”, and
methylmagnesium carbonate (Morenus 119). However, the non-‐aqueous procedure is
based predominantly on surface area, thus it doesn’t have the penetration ability of an
aqueous wash to access the depths of the ink (Banik). A study done by Dr. Chandru
Shahani and Frank Hengemihle determined that an aqueous bath was more effective than
eleven times the quantity of alkaline compound in a non-‐aqueous treatment (Morenus
123). Thus, if a document’s ink is not soluble, a water-‐based process is preferred, despite
the looming conflicts of bleeding and yellowing associated with the aqueous process.
Lastly, the calcium phytate treatment is a favorite of conservators. This compound
acts as a chelating agent, binding with iron(II) and iron(III) ions. Since the iron takes the
place of the calcium in the calcium phytate the iron ions are no longer free. Thus, the iron
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ions cannot increase the rate of the oxidation process; the ink virtually ceases to rust
(Reißland 125). The calcium phytate also works in conjunction with the deacidification
processes. After a record is rid of the spare iron ions, it can be washed with an aqueous
calcium bicarbonate treatment. This alkaline neutralizes the remaining acids in the
document and stops the acid hydrolysis without the extreme yellowing caused by
magnesium deacidifiers. This combination of plans manages to treat both the acidic and
corrosive natures of the iron gal ink. As the chart below demonstrates and Reißland agrees
stating, “calcium phytate/calcium bicarbonate is the most effective treatment to delay ink
corrosion” (125). While this may seem like the dream combination it is not without faults
as a quantity of white powder can precipitate on top of the document after the
deacidification process. This powder is result of the reactions with the sulphuric acid and
calcium ions. These can be easily brushed off without harming the ink or the paper.
Overall calcium phytate and calcium bicarbonate appears to be the most effective paper
conservation technique for iron gall ink.
( Reißland 125)
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While calcium phytate is the best conservation tool, a better option is to preserve a
document so well based on environmental and handling controls that no conservation
efforts are needed to rescue a record from the corrosive, iron gall ink. After a record
undergoes any treatment to increase its durability and life length, the basic chemical
structures of the document and ink undergoes a fundamental change. Even when a record
has a water bath without any chemical additives, the structure of the paper seems to melt
together because of the heat, as shown in the following figure:
(Tse 20)
This principle also holds true for aqueous and non-‐aqueous treatments. As alkaline
compounds neutralize the low pH, the original composition of the physical document and
ink is irreparably lost. This has a huge impact on the library and museum worlds since
chemically preserved documents and records can no longer be identified by their
composition. In its altered form, the record cannot be verified to prove the document’s
history: dating, provenance, authorship, etc. This is especially relevant when rare, famous,
and expensive records are being considered for conservation work. There are also other
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situations when a conservator would not want to change the construction of the document.
If a record still had some of the original blotting paper or sand left stuck to the ink, then it
has a special historical worth that must not be overlooked. Overall using chemicals to
preserve the appearance and context of a document may be inappropriate if it sacrifices the
character and historical value of the piece.
Conservators spend a lot of time and effort getting it right the first time, testing
before they treat because there is no undo button in the real world. This is why it is vital
that the proper conservation methods are used first. In this case the best options are to
preserve records with iron gall ink in cool, low moisture storage facilities or treat them
with calcium phytate and calcium bicarbonate. With this combination of chemical
processes, records are proven to have a longer lifetime without being marred by many
common side effects such as bleeding, fading, cracking, and other blemishes caused by
oxidizing iron or acid hydrolysis. While the decision ultimately falls on the conservator and
his or her experience to determine which conservation technique will best preserve the
record, the best chemical conservation technique offered today effectively terminates the
corrosion of iron gall ink.
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Bibliography
Banik, Gerhard, et al. The Iron Gall Ink Website. Ed. Birgit Reissland and Frank Ligterink.
European Commission on Preservation and Access, Bureau Metamorfoze, the
Cultural Heritage Agency of the Netherlands, 13 Feb. 2011. Web. 16 Apr. 2012.
<http://ink-‐corrosion.org/>.
Morenus, Linda Stiber. “In Search of a Remedy: History of Treating Iron-‐Gall Ink at the
Library of Congress.” The Book and Paper Group Annual 22 (2003): 119-‐125. Web.
16 Apr. 2012 PDF File. < http://cool.conservation-‐
us.org/coolaic/sg/bpg/annual/v22/bp22-‐23.pdf>.
Pedersoli, Jose Luiz, Jr., and Birgit Reißland. "Risk Assessment." N.d. PDF File.
<www.viks.sk/chk/res_4_03_205_226.doc>.
Reißland, Birgit, and Suzan De Goot. "Ink Corrosion: Comparison of Currently Used
Aqueous Treatments for Paper Objects." N.d. PDF file. <cool.conservation-‐
us.org/iada/ta99_121.pdf>.
Tse, Season, et al. "The Effect of Simmering on the Chemical and Mechanical Properties of
Paper." Restaurator and Canadian Conservation Institute Newsletter 36 (Fall 2005):
14-‐35. Germany. Web. 16 Apr. 2012 PDF file.
<http://www.viks.sk/chk/res_1_05_14_35.doc>.