Bertrand Lavédrine

The nature of the extraordinary finish of Stradivari's instruments.

What is Stradivaris “secret”? The composition of the mythical varnish that coats Stradivaris violins has raised controversial assumptions for the past two centuries. By using a complementary array of analytical tools, the chemical microstratigraphy of these varnishes has been established. The results provide information on the materials and techniques that were used by the Master, with a detailed characterization of the varnish.

Room-Temperature Study of Iron Gall Ink Impregnated Paper Degradation under Various Oxygen and Humidity Conditions: Time-Dependent Monitoring by Viscosity and X-ray Absorption Near-Edge Spectrometry Measurements

Many western manuscripts were written using iron gall inks. These inks can damage the paper via two major mechanisms: (a) acid hydrolysis, enhanced by humidity, and (b) oxidative depolymerization provoked by the presence of oxygen and free iron(II) ions. The degradation of unsized Whatman paper impregnated with different combinations of iron sulfate, gallic acid, and gum arabic was studied at room temperature in order to assess the relative importance of each mechanism. The samples were stored in various environments including a dry and/or an oxygen-free atmosphere. The cellulose depolymerization was monitored by viscometry and related to changes in the oxidation state of iron, determined by X-ray absorption near-edge spectrometry. The results indicate that residual amounts of oxygen (less than 0.1%) promote cellulose depolymerization, whereas the level of relative humidity has no impact. The cellulose depolymerization also appears closely correlated to oxidative mechanisms. Regarding the oxidation of iron, it only occurs in the simultaneous presence of oxygen and moisture, suggesting the occurrence of rustlike oxidative mechanisms. Finally, the presence of gallic acid has a strong influence, which is only partially explained by its capacity to reduce iron(III) to iron(II).

Assessment of the degradation of polyurethane foams after artificial and natural ageing by using pyrolysis-gas chromatography/mass spectrometry and headspace-solid phase microextraction-gas chromatography/mass spectrometry

Polyurethane foams are widely present in museum collections either as part of the artefacts, or as a material for their conservation. Unfortunately many of PU foam artefacts are in poor condition and often exhibit specific conservation issues. Their fast thermal and photochemical degradations have been the aim of previous researches. It is now accepted that hydrolysis predominates for polyester-based polyurethane PU(ES) whereas oxidation is the principal cause of degradation for polyether-based polyurethane PU(ET) variety. Only a few studies have been devoted to volatile organic compounds (VOCs) emitted by polyurethanes and, to our knowledge, none were performed on polyurethane foams by using headspace-solid phase microextraction (HS-SPME). The objective of the work described here is to assess the impact of some environmental factors (humidity, temperature and daylight) on the degradation of PU foams by evaluating their volatile fractions. We investigated morphological changes, polymerized fractions and volatile fractions of (i) one modern produced PU(ES) foam and one modern PU(ET) foam artificially aged in different conditions as well as (ii) four naturally aged foams collected from various daily life objects and selected for the representativeness of their analytical data. Characterization procedure used was based on attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and non-invasive headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry (HS-SPME-GC/MS). In this paper, the formation of alcohol and acid raw products for PU(ES) and glycol derivatives for PU(ET) during natural and artificial ageing is confirmed. These main products can be considered as degradation markers for PU foams. Results show that artificial and natural ageing provide similar analytical results, and confirm that the dominant degradation paths for PU(ES) and for PU(ET) are hydrolysis and photo-oxidation, respectively. Lastly, we highlight that non-invasive HS-SPME-GC/MS analysis allows to distinguish between PU(ES) and PU(ET) at any point of their degradations.

Study of the stability of cellulose-holocellulose solutions in N,N-dimethylacetamide-lithium chloride by size exclusion chromatography.

Solutions in N,N-dimethylacetamide (DMAC)-LiCl were prepared from two different pulps (sulphite pulp from softwood and cotton linters) in different ageing states. Degradation of the stirred solutions at 35-40 degrees C was observed by determining the molecular masses by size exclusion chromatography (SEC). We showed that under these conditions cellulose and holocelluloses are degraded in DMAC-LiCl and that the rate of degradation is dependent on the temperature and the initial state of degradation of the sample. Temperature and dissolution time are recommended to be reduced, especially for aged samples.

Identification of synthetic dyes in early colour photographs using capillary electrophoresis and electrospray ionisation–mass spectrometry

Capillary electrophoresis with photodiode array detection (CE-PDA) and with electrospray ionisation-mass spectrometry (CE-ESI-MS) was used for the separation and the identification of 23 synthetic organic dyes, among those used in early 20th century colour photographs such as autochromes. Both cationic and anionic dyes could be separated within 15min using a single CE-PDA method. The method was used as the basis to develop a CE-ESI-MS methodology through the optimisation of the relevant ESI and MS parameters. Sheath liquid composition, nebulising gas pressure, drying gas flow rate and drying gas temperature were found to influence the sensitivity of the detection. These parameters were optimised in positive and negative ion modes for cationic dyes and anionic dyes, respectively. The two analyses could be carried out successively on a single sample. In view of the application to cultural heritage objects, the CE-ESI-MS analytical procedure was applied to identify the dyes in a Filmcolor artefact, late version of the autochrome. The results complemented and enhanced current knowledge as four cationic dyes and three anionic dyes were identified. Four additional dyes are proposed as possibly present as traces.

Capillary electrophoresis with electrospray ionisation-mass spectrometry for the characterisation of degradation products in aged papers

A methodology for capillary electrophoresis/electrospray ionisation mass spectrometry (CE/ESI-MS) was developed for the simultaneous analysis of degradation products from paper among two families of compounds: low molar mass aliphatic organic acids, and aromatic (phenolic and furanic) compounds. The work comprises the optimisation of the CE separation and the ESI-MS parameters for improved sensitivity with model compounds using two successive designs of experiments. The method was applied to the analysis of lignocellulosic paper at different stages of accelerated hygrothermal ageing. The compounds of interest were identified. Most of them could be quantified and several additional analytes were separated.

Paper strengthening by polyaminoalkylalkoxysilane copolymer networks applied by spray or immersion: a model study

Abstract Two di-alkoxysilanes, with (AMDES, aminopropylmethyldiethoxysilane) or without (DMDES, dimethyldiethoxysilane) an amine function, and a tri-alkoxy aminosilane (APTES, aminopropyltriethoxysilane) as well as their mixtures were introduced in paper as fiber strengthening agents. The polymerization and copolymerization of these polysiloxanes in the paper were investigated. In all the cases where APTES was present, the formation of networks was established by measuring the soluble fraction amount extracted from the treated papers. A slight decrease of the opacity of the paper sheets when AMDES was part of the treatment was noted. The presence of APTES reduced this opacity loss. The study of the physicochemical properties of the treated paper (mechanical strength and alkalinity) demonstrated that, besides the required deacidification feature, the different treatments allowed an efficient strengthening of the cellulose fibers to various extents. Contact angle measurements indicated a decrease of the hydrophilic character of papers treated with the mixture APTES/AMDES and the occurrence of a hydrophobic character of the papers treated with APTES alone. These results were consistently obtained for both spray and immersion treatment processes.

An approach of a study of the interaction between collagen and sulphur dioxide by using ESI and MALDI-TOFMS

In order to further understand the interaction between pollutants and collagen, a study with two plain proteins, bovine serum albumin (BSA) and lysozyme, both exposed to SO2 has been carried out. X-ray analysis of the samples using a scanning microscope spectrometer (SEM) was carried out. Samples were analysed by mass spectrometry using an electrospray source coupled to a time of flight analyser (ESI-TOFMS) and by Fourier transform infrared spectroscopy (FT-IR). A chemical cleavage using cyanogen bromide (CNBr) was carried out on BSA exposed to SO2, the CNBr cleavage fragments were analysed by matrix-assisted laser desorption/ionization source coupling to a TOF analyser (MALDI-TOFMS). All these results allow us to determine a hypothesis for the mechanism of the reaction between SO2 and BSA.

THE USE OF SIZE EXCLUSION CHROMATOGRAPHY (SEC) FOR THE EVALUATION OF PAPER DEGRADATION CAUSED BY NITROGEN OXIDES IN COMPARISON WITH OTHER METHODS

Abstract In order to evaluate the deterioration of paper, methods such as pH measurement, viscosity or mechanical properties have found a large application. However, these relatively simple methods have their disadvantages, such as a rather large sample size, application limitations, and significance in regard to paper deterioration. Size exclusion chromatography (SEC) is a promising tool which has been applied to cellulose characterization using dimethylacetamide with lithium chloride as solvent system. SEC is a micro-destructive method which provides the mass weight distribution (MWD) and can indicate its evolution during a deterioration process. SEC was applied in order to obtain the MWD of different types of paper after exposure to nitrogen oxides. Mechanical properties were correlated to the classic methods and to the MWD. This study showed that SEC allows the detection of degradation before the mechanical properties of the paper are modified.

Independent macroscopic chemical mappings of cultural heritage materials with reflectance imaging spectroscopy: case study of a 16th century Aztec manuscript

Reflectance spectral imaging is a powerful tool for the non-invasive study of cultural heritage objects. Particular visible to short wave infrared (400–2500 nm) spectral features are linked to compositional information. Spectral images can hence be used to generate useful chemical maps. However, in the case of complex mixtures, the global shape of reflectance spectra of pure materials can be affected by the presence of other absorbing materials. While studying heterogeneous polychromatic surfaces in which the same material is found in different color preparations (hence presenting different global absorption characteristics), this aspect can strongly affect the success of the targeted chemical mapping. As a result, several spectral processing steps are necessary to overcome the presence of interfering materials. The case study of the Codex Borbonicus, a precious 16th century Aztec manuscript, is reported herein. Visible and short-wave infrared reflectance images of the document were scanned in situ. To obtain material specific mappings that are not affected by the presence of pigment mixtures, the necessity of applying particular spectral treatments is shown. The flaws and qualities of the resulting chemical images are discussed, along with their general potential for cultural heritage case studies. In summary, independent macroscopic chemical maps of cochineal lake, gypsum, and palygorskite (the clay that composes the mineral matrix of the famous Maya Blue pigment) on the pages of the manuscript were successfully obtained.