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Gels prepared from the polysaccharide gellan are used for aqueous poulticing treatments in paper conservation when the application of water must be restricted. Optimal use of the rigid, yet shapeable gel requires direct contact with the paper surface, which carries the risk of gel residues on the treated surface. We used acid methanolysis as a destructive analytical method to detect rhamnose as a component of gellan, which was undetectable with ATR-FTIR spectroscopy. We show that there is a significant probability of leaving gellan residues on the paper. Conservators should be aware of this potential side effect when considering the use of gellan poultices in direct contact with paper objects.

Six face- and back-mounted chromogenic print samples (each 120 × 160 cm) and one pre-damaged original photograph (120 × 120 cm) were exposed to alternating temperature conditions. Cold storage was set at 8 °C with a slightly fluctuating relative humidity at an average of 55 % in a cooling chamber; room temperature storage occurred at 19 to 27 °C depending on the prevailing weather conditions. The samples were exposed alternatingly to these setups in a 24-hour rotation over five weeks to assess the effect of strong and rapid fluctuations on the stability of the composite. After about one week under the extreme, stress-intensive testing conditions, irreversible deformation, and a local loss of translucency occurred. Further local delamination was observed on the pre-damaged original artwork. Exceeding the dew point temperature, which occurred in our experimental setup and should be avoided, resulted in condensation on the acrylic surface and led to extensive streaks and, in combination with the electrostatic charge, to extreme dust deposits. These findings suggest that cold storage cannot be recommended for face- and back-mounted chromogenic prints.

Newly produced face-mounted photographic prints feature perfectly clear, smooth acrylic surfaces. Cleaning these integral but vulnerable surfaces poses a high risk of mechanical damage, which increases with every repetition. We tested the mechanical impact of dry-cleaning to optimize the cleaning process of face-mounted artworks at the Kunstsammlung Nordrhein-Westfalen in Düsseldorf. We used four different microfibre cloths on one acrylic common in the production of face-mounted photographs. One additional option consisted of an antistatic silicone roller used for preliminary cleaning on one half of the plates. The plates were contaminated with street particulate soiling and fingerprint stains. All glasses were cleaned in either circular or straight wiping motions. The plates were photographed in dark field to document any side effects of cleaning involving scratches, smudges, and the static charge of the acrylic after cleaning. The microfibre cloth SM 711 in combination with the silicone roller performed best in the test. However, the same cloth, pre-used and washed, significantly increased scratch formation. These findings provide effective and safe recommendations for risk-minimized future cleaning procedures for face-mounted photographs.

ABSTRACTChemical conversion of darkened lead white into white lead(II) sulfate with hydrogen peroxide (HP) may impact the surrounding paper, depending on treatment parameters. Side effects of historic conversion treatment are illustrated by a drawing by Abraham Bloemaert. Model papers rendered HP-sensitive by iron(II) sulfate impregnation and prepared with darkened lead white underwent conversion with HP in gas, gel or liquid form. Visual (VIS, magnification) and instrumental (single gas detection with Dräger X-am® 5100) analysis revealed that no application method was free of side effects and that HP gas emission continued for a considerable time after 3% HP application by brush.

ABSTRACTThe three treatment phases for pressure-sensitive tape removal included in this review are: removal of the carrier, adhesive removal from the paper surface, and adhesive removal from the paper interior. The latter process requires organic solvents. Solvent selection via the Teas chart or Zumbühl’s system are compared. Teas triangular chart supports the calculation of solvent mixtures with ideal mixing properties; Zumbühl’s bi-axial parametrization system supports solvent selection when solvent mixtures exhibit non-ideal behaviour and highlights vapour pressure as the solvent selection criterion. Strategies for working with solvents include a discussion of solvent mixtures and their application and the introduction of a suction disk design. Effects and common side effects of treatment are presented with examples. This review supports novices and practitioners in their treatment choices when dealing with the removal of pressure-sensitive tapes.

ABSTRACTAmong bleaching agents available in paper conservation, hydrogen peroxide (HP) is a versatile choice that has many advantages in the removal of discoloration from paper. However, its well-known radical formation in the presence of iron impurities in paper poses the risk of cellulose degradation and color reversion, i.e. return of staining. This study explores a method to diminish undesired HP reactions by adding an additional step using a calcium phytate solution as complexing agent to the recommended treatment sequence. Tests on model papers impregnated with different molar concentrations of iron ions to trace the effects of simulated HP treatments on weight average molar mass, carbonyl group content, and color indicate that the iron phytate complex is sufficiently stable to sustain limited HP bleaching and thereby keeps the iron ions to a certain extent from the reaction system.

5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores in cellulosic materials. Its almost ubiquitous presence in cellulosic materials makes it a target molecule of the pulp and paper industry’s bleaching efforts. In the presented study, DHNQ was treated with hydrogen peroxide under alkaline conditions at pH 10, resembling the conditions of industrial hydrogen peroxide bleaching (P stage). The reaction mechanism, reaction intermediates, and final degradation products were analyzed by UV/vis, NMR, GC–MS, and EPR. The degradation reaction yielded C1–C4carboxylic acids as the final products. Highly relevant for pulp bleaching are the findings on intermediates of the reaction, as two of them, 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) and 1,4,5,8-naphthalenetetrone, are potent chromophores themselves. While DHBQ is one of the three key cellulosic chromophores and its degradation by H2O2is well-established, the second intermediate, 1,4,5,8-naphthalenetetrone, is reported for the first time in the context of cellulose discoloration.

Bleaching in paper conservation is a complex, highly invasive treatment that involves decisions regarding cultural, aesthetic, technical and scientific parameters. We present an overview of key requirements of bleaching that can be considered a basis for future standards and guidelines. In this context, we look at the function of standards and guidelines as regulatory documents supporting decision-making and quality control in complex professions where material and immaterial values factor into decision-making. Furthermore, a bleaching case involving light and hydrogen peroxide steps exemplifies the often neglected but essential treatment skill expertise in choosing and adjusting steps continually in response to the object’s requirements. Bleaching treatment is argued to be part of scientific practice when it is conducted on the grounds of current professional knowledge and is reflected systematically so that it can contribute experiential knowledge to this practice.

The results of a research project on verdigris on paper have been applied in the conservation of a celestial atlas and a series of printed books with images of cities in Renaissance time. Paper degraded by verdigris was chemically stabilized by applying a solution of benzotriazole, a copper complexing agent, in ethanol by brush from the verso. Tears and brittle areas were mechanically stabilized with pre-coated Japanese tissue papers. The copper ion content and the effect of complexation were monitored with self-prepared copper ion indicator papers. Paper samples with different concentrations of benzotriazole were light-aged to evaluate the effect of yellowing.

Nach einer kurzen Einführung in die Technologie der Papierherstellung und der Mengenentsäuerung werden zunächst die Entwicklungen auf dem Gebiet der Qualitätskontrolle aufgezeigt. Zurzeit sind der pH-Wert, die alkalische Reserve und ihre Verteilung die Hauptkriterien zur Bewertung des Behandlungserfolgs. Da diese destruktiven Messmethoden nicht an Originalobjekten erfolgen können, muss ein universell einsetzbares Testpapier definiert werden. Im Wesentlichen muss dieses Testpapier das Absorptionsverhalten eines Entsäuerungsreagenzes und dessen Reaktionen mit im Papier vorhandenen Säuren darstellen können. Passend dazu müssen entsprechende Messmethoden den Entsäuerungserfolg zweifelsfrei darstellen können. Mit der Kombination von geeignetem Testpapier und spezieller Celluloseanalyse wurde hier im Rahmen der ISO / TS 18344 ein neuer Weg beschritten.

Copper pigments promote the deterioration of paper objects; hence, it has been problematic to paper conservation since many valuable historical manuscripts contain copper green pigments. In particular, verdigris yields relatively mobile copper ions that can cause a higher risk of degradation depending on the relative humidity of the storage conditions. Although several research studies have demonstrated potential chemicals to slow down the degradation of the paper with copper ions or copper pigments, passive treatments such as mechanical reinforcement or environmental controls are still preferred since wet chemical treatments need to be further investigated. In the present study, various wet chemical treatments of rag paper with verdigris are tested with consideration for the practical situations of application as well as the sample conditions. GPC-Fluorescence-MALLS system after fluorescence labeling of carbonyl groups of cellulose was employed to evaluate the inhibition of both, hydrolysis and oxidation of cellulose after treatments. Samples were prepared to simulate a partially soluble verdigris pigment bound in gum arabic on gelatin-sized rag paper. With the given sample conditions, beneficial effects from deacidification was rather limited despite the use of a mixture of water and ethanol as a co-solvent. In contrast, treatments with tetrabutylammonium bromide in ethanol or 1H-benzotriazol in ethanol showed significant stabilization of the samples. For both cases, hydrolytic degradation and oxidation of cellulose were retarded significantly when brushing application on verso was employed. Testing various conditions of the solutions and two different application methods led to the conclusion that the outcome of the solution treatment depends on not only the chemical, but also how it is applied.

Cellulose wird als Hauptbestandteil von Papier und Textilien seit Jahrtausenden verwendet. Restaurierung und Konservierung wertvoller historischer cellulosischer Objekte gehen mit Neuerungen in der Cellulosechemie und ‐analytik Hand in Hand.

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC‐MALLS was used to get a deeper insight into ink‐induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied.

Summary:Copper corrosion on paper works of art is commonly explained by copper ion‐catalysed cellulose oxidation, usually reflected by discoloration of pigment and surrounding paper as well as by loss of mechanical strength. In this study, model paper and historic paper samples, both containing copper pigments, were compared using fluorescence labelling of carbonyl groups and subsequent GPC analysis. The historic paper samples did not show any typical sign of copper pigment induced discoloration, but high brittleness. In artificially copper‐corroded paper samples the distribution of carbonyl groups in combination with the molecular weight distribution of cellulose clearly indicated the occurrence of oxidative processes. In contrast, only insignificant oxidative damage was detected in the case of the paper fragments from an original work of art, a codex from the 15thcentury. Here, mostly degradation by hydrolytic action was revealed. There was no introduction of carbonyl groups into the bulk section of the molecular weight distribution, and the gain in new carbonyl groups corresponded to the number of reducing end groups newly generated by hydrolysis.

Deterioration of historical papers is caused by several processes, such as acid hydrolysis or autoxidation due to the presence of metal ions contained in inks or pigments. Both processes can be studied by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS. This technique allows to determine not only the extent of hydrolysis, but also the concentration of oxidized functionalities within very low sample amounts.Deterioration of historical papers is caused by several processes, such as acid hydrolysis or autoxidation due to the presence of metal ions contained in inks or pigments. Both processes can be studied by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS. This technique allows to determine not only the extent of hydrolysis, but also the concentration of oxidized functionalities within very low sample amounts.

Summary.The present paper examines oxidative degradation of cellulose catalyzed by presence of Cu1+and Cu2+ions in the context of historic paper conservation treatments. Aqueous treatments of degraded papers further spread transition metal ions, such as copper, across the fibre matrix, and therefore augment the detrimental effect of these ions. In the paper industry, the inhibiting effects of magnesium ions on metal‐catalyzed degradation of cellulose contaminated with metal impurities have been observed. Also, magnesium compounds dissolved in alcoholic or aqueous solutions are generally used in paper conservation as deacidification agents. Paper samples with artificially produced copper corrosion served as mock‐ups for examination and comparison of different treatments which focused on the inhibiting effect of magnesium and antioxidants. Analytical examination of molecular weight distribution, carbonyl content, carboxyl content, and surface pH was performed. Results show an inhibiting effect of magnesium on copper‐catalyzed cellulose degradation, although less pronounced than expected.

The viability of fiber optics reflectance spectroscopy (FORS) for the differentiation of red chalk drawing media was investigated, focusing on the group of drawings from the workshop of Giovanni Battista Piranesi (1720–1778) at the Staatliche Kunsthalle Karlsruhe, Germany. The evaluation of spectra was supported by principal component analysis (PCA). The method was tested on mock-up drawings made with recently acquired natural and synthetic red chalks of known origin. It was possible to sort these mock-up drawings according to chalk type and application technique. The compositional differences of these reference chalks were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Subsequent FORS analysis of selected original drawings revealed the existence of several closely grouped clusters, implying similarities on the basis of the underlying spectral features among the historical red chalks used in Rome. These similarities distinguished the historical drawings from the red chalk mock-up drawings, except for the drawings made with red chalk samples from the area near the town of Theley, Germany, which were shown to bear close similarities to those in the cluster of historical samples.