Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 1: model paper studies

Cellulose in historic paper documents is often damaged by the writing media used, especially iron gall ink or copper pigments. Degradation induced by iron gall ink is suggested to be a synergistic process comprising both hydrolytic and oxidative reactions. These processes were studied on very low sample amounts according to the CCOA and FDAM method, i.e. by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS, respectively. This study focused on preventive means to stop the deterioration induced by iron gall ink of cellulose and to prevent further damage, keeping in mind that a suitable conservation treatment has to hinder both, hydrolytic and oxidative processes, at the same time. A combination of the complexing agent calcium phytate and calcium hydrogencarbonate in aqueous solution was proved to give optimum results. To gain insight into long term stability, an aging step was performed after treatment and different ink modifications were tested. Recording the molecular weight distributions and the carbonyl group content over time GPC analysis verified for the first time the preventive effect of this treatment. This effect was not only seen for the ink-covered areas, but extended also to areas remote from the ink lines. Ink containing copper ions responded equally positively to the calcium phytate/hydrogencarbonate treatment as the iron gall ink papers did. Gelatine, sometimes used in a similar way due to an alleged cellulose-stabilizing effect did not have a beneficial influence on cellulose integrity when metal ions were present.     

Historical iron gall ink containing documents — Properties affecting their condition

Iron gall ink, also referred to as iron gallotannate ink, is one of the most important inks in the history of western civilisation, and was in widespread use from the middle ages until the 20th century. Unfortunately, iron ions and acids present in these inks induce enhanced degradation of paper, thus severely damaging numerous historical artefacts. Yet, when examining documents, it is frequently observed that not all materials containing iron gall ink are suffering from ink corrosion. While some are completely destroyed, others may be in excellent condition even centuries after their creation. In order to establish the main properties of materials, common to severely degraded documents, the effects of the type and quantity of metal ions in the ink, as determined by in-air PIXE method, pH of the ink on paper, grammage of paper, its absorptivity and the width of ink lines were evaluated against the extent of corrosion. Using multiple linear regression analysis, a correlation has been obtained between the width of the applied ink lines, pH, grammage of paper and the extent of ink corrosion. Based on these factors, which can be acquired non-destructively from most historical documents, it is therefore possible to predict the stability of historical iron gall ink containing paper.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 2: application on historic sample material

Degradation of cellulose in historic paper by iron gall ink is a synergistic process of both, acid hydrolysis caused by acidic ink ingredients and oxidation catalyzed by free iron and/or copper ions. The interplay of both reactions was studied according to the CCOA method on historic paper samples. Only minute amounts (few mg) of the samples were required to obtain profiles of naturally present and oxidatively introduced carbonyl groups, which was done by group-selective fluorescence labeling in combination with determination of the molecular weight distribution by GPC-MALLS. In the present study naturally occurring degradation pathways in historic sample papers have been investigated. Different extents of oxidatitive degradation were shown for paper with and without ink. A typical pattern of the molecular weight distribution in naturally aged papers was identified, the peculiar feature being a distinctive shoulder in the region of low molecular weight, roughly between 25,000 and 5,000 g/mol corresponding to a DP between 150 and 30. This pattern was a typical attribute of degraded natural samples: any artificial aging procedures aimed at modeling natural aging processes must thus attempt to reproduce this feature. Although the historic samples had been more severely oxidized than model papers, the inhibition of further oxidation and hydrolysis by the calcium phytate/hydrogen carbonate treatment was evident and could be proven for the first time on the molecular level. Also on plain paper without ink application the oxidation was suppressed and the molecular weight was stabilized on a high level.     

Study of the copper effect in iron-gall inks after artificial ageing

Iron-gall inks consist of a mixture of vitriols (sulphates of certain metals), gall nut extracts and arabic gum. The association of the iron(II) sulphate present in vitriols, and the gallic acids present in the gall nut extracts induces, after exposure to oxygen, the formation of dark coloured compounds of ink. In addition to iron, this kind of inks contains other metals, such as copper, zinc, and nickel. Among them, copper could be considered the most important because, owing to its catalytic ability, it can be involved in the processes concerning formation and stability of iron complexes, which are responsible for the ink dark colour. For this purpose, four different iron-gall inks containing increasing amounts of copper sulphate were prepared according to a traditional receipt and applied on paper supports. The ink-stained paper specimens were subjected to an intense analytical program to investigate their chemical and physical modifications after artificial ageing (both temperature/humidity and ultraviolet light ageing). The role of copper in the iron-gall inks was evaluated using optical microscopy, colorimetric measurements, X-ray fluorescence (XRF), X-ray diffraction analysis (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) and Fourier transform infrared spectroscopy (FTIR). For the evaluation of the oxidation state of iron and copper, X-ray absorption spectroscopy (XANES) was used. All results indicate that the presence of copper in iron-gall ink causes colour variation, affects the migratory behaviour of iron in the paper, increases the formation of secondary products particularly when ageing process based on temperature/humidity variations is considered.     

毛细管电泳法基于Fe(Ⅱ)与Fe(Ⅲ)的比值识别签字笔字迹的相对书写时间

可疑文件中墨水笔迹的相对时间鉴定对法庭科学、刑事案件的侦破和历史文献的整理都具有重要意义。该文建立了一种识别墨迹相对年代的毛细管电泳（CE）新方法。采用络合剂邻菲罗啉（1,10-phen）和反式-1,2-环己二胺四乙酸（CDTA）分别与Fe（Ⅱ）和Fe（Ⅲ）络合,然后用CE测定Fe（Ⅱ）和Fe（Ⅲ）的峰面积,通过比较从可疑笔迹中提取的Fe（Ⅱ）和Fe（Ⅲ）的峰面积比与从整个文档中提取出的Fe（Ⅱ）和Fe（Ⅲ）的峰面积比,判断整篇文字是否同时书写。实验首先对两种络合剂与两种价态铁离子的特异性络合进行了研究,结果表明1,10-phen与Fe（Ⅱ）、CDTA与Fe（Ⅲ）具有特异性络合。初步研究还表明：由于商用墨水pH值较低,墨水中的Fe（Ⅱ）在墨水瓶中比较稳定,因此Fe（Ⅱ）在墨水瓶中的氧化可以忽略不计;但当墨水书写在纸张上时,墨水中的硫酸会逐渐被纸张的纤维素所消耗,从而导致Fe（Ⅱ）在纸张中被逐渐氧化;在老化过程中Fe（Ⅱ）和Fe（Ⅲ）的峰面积比发生了变化,书写的时间越长,Fe（Ⅱ）和Fe（Ⅲ）的峰面积比就越小。该技术的成功应用依赖于找到一种合适的提取笔迹墨水的方法和CE分离测定Fe（Ⅱ）和Fe（Ⅲ）的方法。样品前处理程序如下：剪取1 cm长的墨水迹线,剪碎后放入2 mL的EP管中,加入0.5 mL 5 mmol/L的1,10-phen萃取1 min,再加入0.5 mL 20 mmol/L的CDTA振荡10 min,10000 r/min离心15 min,取上清液进行CE分离检测。CE条件如下：熔融石英毛细管（40.2 cm（有效长度30 cm）×75 μm i.d.）,100 mmol/L硼酸-硼砂缓冲溶液（pH 9.2）,压力上样（1.379 kPa,上样时间5 s）,分离电压20 kV,检测波长254 nm,温度控制在25℃。最后,对两种不同的墨水进行了测定,以评价所建方法的适用性,结果表明所建方法对于鉴别可疑文件中真伪笔迹的相对年代具有重要的指导意义。     

Thermal analysis and the scientific conservation of cultural materials

Prior to treatment, letters dating from 1665–66 were characterised using SEM, FTIR, ESCA or XPS, TG, TMA and DLTMA. All three papers were similar in composition and were basically cellulosic materials. Two which had been sent from Lisbon contained trace amounts of Fe and Cu; these impurities were also present in a letter sent from Dublin. All three letters had been written with iron gall ink. The letter from Dublin had an additional feature in the ink in the form of small bright specks of mica. The papers were examined after conservation treatment using the above same techniques in an attempt both to determine and quantify any changes which had occurred during the treatment process. Scanning electron micrographs showed that propounced changes had occurred to the surfaces of the treated papers. With XPS it was possible to measure the change in the surface composition of the papers which occurred on treatment. It was also found that the treatment reduced the thermal stability of the papers in all three cases.     

Simplification of Ink Dating for Forensic Analysis by Thermal Microdesorption Gas Chromatography–Mass Spectrometry

A simplified procedure for obtaining measurements useful for ink dating is presented for forensic analysis. A thermal microdesorption device was employed with gas chromatography–mass spectrometry (GC-MS). The release of phenoxyethanol from the ink entries on paper was studied at several temperatures during a single analysis. A separate thermal desorption unit was not required. Two methods measuring the amount of phenoxyethanol liberated at four temperatures and two temperatures were proposed. The effect of heating of ink samples to 70?°C for 30?minutes applied to fresh and old samples was studied. An illustration how to distinguish between fresh and old samples by the analysis of the same ink entry after the time period of two months is provided.     

Chemometric tool for identification of iron–gall inks by use of visible–near infrared fibre optic reflection spectroscopy

A method has been developed for identification of corrosive iron–gall inks in historical drawings and documents. The method is based on target-factor analysis of visible–near infrared fibre optic reflection spectra (VIS–NIR FORS). A set of reference spectra was obtained from model samples of laboratory-prepared inks covering a wide range of mixing ratios of basic ink components deposited on substrates and artificially aged. As criteria for correspondence of a studied spectrum with a reference spectrum, the apparent error in target (AET) and the empirical function SPOIL according to Malinowski were used. The capability of the proposed tool to distinguish corrosive iron–gall inks from bistre and sepia inks was evaluated by use of a set of control samples of bistre, sepia, and iron–gall inks. Examples are presented of analysis of historical drawings from the 15th and 16th centuries and written documents from the 19th century. The results of analysis based on the tool were confirmed by XRF analysis and colorimetric spot analysis.

Establishing the irradiation dose for paper decontamination

Museums, libraries and archives are preserving documents that are slowly degrading due to the inherent ageing of the cellulose substrate or to the technological errors of the past (acid paper, iron gall ink). Beside this, large quantities of paper are rapidly damaged by biological attacks following natural disasters and improper storage conditions.The treatment of paper documents with ionizing radiation can be used for mass decontamination of cultural heritage items but conservators and restaurators are still reserved because of the radiation induced degradation.We conducted a study for establishing the dose needed for the effective treatment of paper documents, taking into account the biological burden and the irradiation effects on paper structure. We used physical testing specific to paper industry and less destructive analytical methods (thermal analysis).Our results show that an effective treatment can be performed with doses lower than 10 kGy. Old paper appears to be less affected by gamma radiation than recent paper but the sampling is highly affected by the non-uniform degree of the initial degradation status. The extent of testing for degradation and the magnitude of acceptable degradation should take into account the biological threat and the expected life time of the paper documents.     

Paper conservation methods: a literature review

The main paper conservation methods are presented, classified in the following categories: preparation of the intervention, disinfestation and disinfection/sterilization, surface/dry cleaning, wet cleaning, chemical stabilization, paper repairs, consolidation and strengthening. Treatment documentation is also discussed. The targets, the historical aspects, the general principles, the materials and equipment, the acceptance and criticism pertaining to each method are briefly reviewed, and the most important research for their evaluation is presented. Several paper stabilization strategies, such as deacidification and iron gall ink stabilization, applicable to paper are elucidated. Specific consolidation and strengthening methods for paper, such as lamination and paper splitting are also discussed. The review mainly focuses on the established methods, but experimental, abandoned or insufficiently documented methods are also included. Shortcomings and limitations of several methods were found in the literature, concerning health issues, limited effectiveness, adverse side-effects on the treated artefacts and restricted applicability.     

Ion paired chromatography of iron (II,III), nickel (II) and copper (II) as their 4,7-Diphenyl-1,10-phenanthroline chelates

A reversed phase ion-paired chromatographic method that can be used to determine trace amounts of iron (II,III), nickel (II) and copper (II) was developed and applied to the determination of iron (II) and iron (III) levels in natural water. The separation of these metal ions as their 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) chelates on an Inertsil ODS column was investigated by using acetonitrile-water (80/20, v/v) containing 0.06 M perchloric acid as mobile phase and diode array spectrophotometric detection at 250-650 nm. Chromatographic parameters such as composition of mobile phase and concentration of perchloric acid in mobile phase were optimized. The calibration graphs of iron (II), nickel (II) and copper (II) ions were linear (r > 0.991) in the concentration range 0-0.5, 0-2.0 and 0-4.0 mug ml(-1), respectively. The detection limit of iron (II), nickel (II) and copper (II) were 2.67, 5.42 and 18.2 ng ml(-1) with relative standard deviation (n = 5) of 3.11, 5.81 and 7.16% at a concentration level of 10 ng ml(-1) for iron (II) and nickel (II) and 25 ng ml(-1) for copper (II), respectively. The proposed method was applied to the determination of iron(II) and iron(III) in tap water and sea water samples without any interference from other common metal ions.     

Development of ultrasound-assisted emulsification solidified floating organic drop microextraction for determination of trace amounts of iron and copper in water, food and rock samples

A simple and efficient liquid-phase microextraction technique was developed using ultrasound-assisted emulsification solidified floating organic drop microextraction combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of iron and copper in real samples. 2-Mercaptopyridine n-oxide was used as chelating agent and 1-dodecanol was selected as extraction solvent. The factors influencing the complex formation and extraction were optimized. Under optimum conditions, an enrichment factor of ~13 was obtained for both iron and copper from only 6.7 mL of aqueous phase. The analytical curves were linear between 40–800 and 20–1,200 μg L^?1 for iron and copper respectively. Based on three SD of the blank, the detection limits were 8.6 and 4.1 μg L^?1 for iron and copper respectively. The relative SDs for ten replicate measurements of 500 μg L^?1 of metal ions were 2.9 and 1.2 for iron and copper respectively. The proposed method was successfully applied for determination of iron and copper in environmental waters and some food samples including chess, rice, honey and powdered milk. Finally, method validation was made using rock certified reference material. A student’s t test indicated that there was no significant difference between experimental results and certified values.     

A pre-concentration procedure using coprecipitation for determination of lead and iron in several samples using flame atomic absorption spectrometry

The present paper proposes a pre-concentration procedure for determination of lead and iron in several samples by flame atomic absorption spectrometry. In it, lead(II) and iron(III) ions are coprecipitated using the violuric acid-copper(II) system as collector. Afterwards, the precipitate is dissolved with 1 M HNO₃ solution and the metal ions are determined. The optimization step was performed using factorial design involving the variables: pH, violuric acid mass (VA) and copper concentration (Cu).Using the optimized experimental conditions, the proposed procedure allows the determination these metals with detection limits of 0.18 μg L⁻¹ for iron and 0.16 μg L⁻¹ for lead. The effects of foreign ions on the pre-concentration procedure were also evaluated and the results demonstrated that this method could be applied for determination of iron and lead in several real samples. The proposed method was successfully applied to the analysis of seawater, urine, mineral water, soil and physiological solution samples. The concentrations of lead and iron achieved in these samples agree well with others data reported in the literature.     

Can electrospray ionization help the characterization of iron gall inks? Investigation on the interactions of gallic acid with iron ions in aqueous solutions

In the present work, an investigation has been conducted by electrospray ionization (ESI) experiments to characterize the structures of iron gall ink complexes in solution. Simple mono and polyphenolic acid molecules added to iron sulfate salts were chosen to model the recipes of ink composition. Theoretical calculations have been used (1) to determine the stability of the ionic complexes generated in the gas phase, (2) to explain which structures are more likely generated in the electrospray ion source, and (3) to determine which mechanisms are likely involved in their formation. Fragmentation pathways of the derived structures have also been investigated and rationalized to facilitate the interpretation of the data obtained under collisionally induced dissociation (CID) conditions.The present study confirms the assumption that ESI experiments with ions that are preformed in solution must be considered carefully. As a matter of fact, the study of ion formation mechanisms in the ion source is necessary to establish relationships between the ion structures in the condensed phase and the gas phase.     

EPR study of iron-doped MFI zeolite and silicalite catalysts: effect of treatments after synthesis

The systematic study of iron-doped MFI zeolite and MFI silicalite by X- and Q-band EPR spectroscopy is reported in this paper. Both samples, which contain Fe(III) ions in the MFI lattice, underwent three sequential treatments—calcination, steaming, and washing with sodium dithionite solution—which are needed to make the catalyst active by extracting iron ions from the lattice. EPR spectra could be simulated by assuming a broad distribution of spin-spin (zero-field) coupling parameters. The simulation parameters depend on sample history and reproduce the selective intensity changes that are observed in X-band spectra after each treatment. In particular, the distribution width decreases by calcining and steaming samples and then it increases by treating with aqueous dithionite solution. This is in agreement with the view that iron ions are extracted from the framework by calcining and by steaming and may form relatively large iron oxide particles which become smaller after the chemical treatment. We have also studied the temperature dependence of the EPR spectra. The most interesting results are from the steamed samples. Their behavior has been interpreted as due to the presence of superparamagnetic single domain particles of iron oxide. This agrees with the view that iron oxide particles form during steaming.     

碘量法连续测定选矿废水中的铜铁

针对选矿废水中的铜离子和铁离子,在滴定铜离子含量的基础上,向滴定液中继续加入三氯化铝溶液作为解蔽剂将铁离子解蔽,此时溶液呈深棕色,以硫代硫酸钠标准溶液继续滴定铁,溶液深棕色消失转为奶白色即为滴定终点,避免了单独滴定铜铁含量的麻烦,且在滴定铁离子含量时无需除铜。经实验验证,对选矿废水中铁含量进行滴定与重铬酸钾滴定铁含量的结果一致,相对误差小于2.03%,加标回收率在95.8%~101.9%,相对标准偏差(RSD,n=10)在0.48%~1.5%。方法精密度高,重现性好,简便快捷,可以满足选矿废水中铜、铁含量的测定要求。