Christian Degrigny

Chloride Removal From Archaeological Cast Iron by Pulsating Current

Abstract The electrochemical stabilization of archaeological cast iron, currently used in restoration and conservation, is designed to extract chlorides by applying an electrical field between the metal (object containing a metal core), which is cathodically polarized, and a stainless steel cage, which is anodically polarized. However, stabilization of artifacts in potentiostatic mode is a relatively long procedure and weakens the artifacts because of the hydrogen evolution when the applied voltage is too negative. In an effort to reduce the secondary effects caused by hydrogen, we decided to study the use of pulsating currents. The aim is to be selective with respect to the reactions produced and to increase the rate of dechlorination treatment. By applying a pulsating signal with a constant current and a limit potential (Elim, Elim <E), the same quantity of chloride (100%) was extracted in the same treatment time as in potentiostatic mode. After optimizing the pulse parameters (i, ton, toff, Elim), the extraction ratio (QCl/Qtotal) increased from 0·17 (potentiostatic mode) to 0·49 (pulsating mode) and side-effects due to hydrogen were avoided.

Benzotriazole as inhibitor for copper with and without corrosion products in aqueous polyethylene glycol

Electrochemical methods, including polarization experiments and impedance spectroscopy, were used to evaluate the effectiveness of benzotriazole (BTA) in an aqueous solution of polyethylene glycol (PEG) in protecting polished archaeological copper or archaeological copper covered with corrosion products. The adsorption of PEG on the polished copper significantly limited the corrosion current. The presence of benzotriazole enhanced the protection of the polished copper, giving maximum protection at a concentration of 10−2 mol l−1 of BTA in 20 vol% PEG 400 solution. On the other hand, PEG solutions caused degradation of the corrosion products of the copper. This degradation increased with time. When BTA was added, the corrosion products were preserved and, the higher the BTA concentration, the more the corrosion current decreased. In PEG 400 solution protection of the corrosion products of the copper by BTA improved over time.

Use of artificial metal coupons to test new protection systems on cultural heritage objects: manufacturing and validation

Abstract New protection systems for cultural heritage artefacts can be tested and their efficiency, compared to traditional systems, assessed using artificial metal coupons. The manufacturing of these coupons requires though a thorough investigation of the artefacts that they are supposed to simulate. Not only their composition, but their surface preparation (through artificial or natural aging) should copy as closely as possible real artefacts. Protection systems tested should be applied according to standardised protocols, while short term testing in humid chamber and long term testing on site should be monitored regularly to detect any possible failure. Only then the use of such artificial metal coupons will be validated. This approach is illustrated in this paper through the EU PROMET and Swiss POINT research projects.

A new electrolytic pencil for the local cleaning of silver tarnish

The prototyping of a newly designed electrolytic pencil for the local cleaning of silver tarnish on artifacts comprising inseparable organic components is described. The pencil helps determine the type and amount of tarnish, define the cleaning parameters (treatment potential and duration), and provides a safe and efficient way to locally and electrolytically reduce silver tarnish. The electrolyte is conveyed to and from the surface of metal objects via a micro-porous foam and is continuously renewed by two pumps. This user-friendly and ergonomic pencil is distributed as an open source kit for self-assembly with parts fabricated using innovative and low-cost technologies. The operating modes for the pencil are described. To evaluate this new tool, the pencil was used to clean a selection of tarnished silver components from composite masterpieces in the Treasury of Saint-Maurice Abbey.

Monitoring Treatments of Waterlogged Iron-Wood Composite Artifacts Using Host Acor IT-PEG 400 Solutions

Abstract Treatment of waterlogged iron and iron-wood artifacts using PEG 400 solutions with and without Hostacor IT was monitored to determine if the inhibitor is effective long-term in stabilizing iron embedded in wood. Corrosion potentials of iron were taken on a daily basis for around two months and were compared to potentiodynamic measurements conducted for iron under the same treatment conditions. The pH, chloride and bioactivity contents of the solutions were also measured. The results show that Hostacor IT is effective in slowing down the corrosion of exposed iron in PEG 400 solutions. However, the corrosion potentials for iron embedded in wood in PEG 400 with Hostacor IT do not suggest passivation by the inhibitor. Also, the bioactivity contents were much higher for PEG 400 solutions with Hostacor IT than without. During treatment, biofilms surrounded iron nails in PEG 400 solution with or without Hostacor IT but were found not to affect the passivation of iron by Hostacor IT. Finally, this study describes how conservators can monitor treatments of iron-wood composite artifacts using corrosion potentials, and can compare their findings to the results of this study.

Colour and Space in Cultural Heritage: Key Questions in 3D Optical Documentation of Material Culture for Conservation, Study and Preservation

The paper introduces some key interdisciplinary questions concerning the development of optical measuring techniques and electronic imaging applied to documentation and presentation of artefacts, as identified through the work of Colour and Space in Cultural Heritage (www.COSCH.info), a trans-domain European Action (TD1201) in the area of Materials, Physics and Nanosciences (MPNS) supported, since 2013, by the European Cooperation in Science and Technology http://www.cost.eu/domains_actions/mpns/Actions/ TD1201. Some 125 international researchers and professionals participate in COSCH activities which have been organised around six main subjects: (1) spectral object documentation; (2) spatial object documentation; (3) algorithms and procedures; (4) analysis and restoration of cultural heritage surfaces and objects; (5) visualisation of cultural heritage objects and its dissemination; and (6) the semantic development of the COSCH Knowledge Representation.

Colour and Space in Cultural Heritage: Interdisciplinary Approaches to Documentation of Material Culture

Colour and Space in Cultural Heritage (www.COSCH.info) is a transdomain European Action (TD1201) in the area of Materials, Physics and Nanosciences (MPNS). The Action runs from 2013 to 2017 and benefits from the support of the European Cooperation in Science and Technology http://www.cost.eu/domains_actions/mpns/Actions/TD1201. The Authors are active participants of the COSCH network. They represent different disciplines involved in documentation and conservation of material cultural heritage. COSCH aims to enhance applications of optical measuring techniques and electronic imaging in this area. The paper outlines scientific, theoretical and practical solutions promoted by COSCH. COSCH activities have been organised around six main subjects: (1) spectral object documentation; (2) spatial object documentation; (3) algorithms and procedures; (4) analysis and restoration of cultural heritage surfaces and objects; (5) visualisation of cultural heritage objects and its dissemination; and (6) the semantic devel...

Interdisciplinarity of Cultural Heritage Conservation Making and Makers: Through Diversity Towards Compatibility of Approaches

In conservation of cultural heritage (CCH), experts from diverse areas of knowledge work together, each of them contributing unique expertise. However, in modern dynamic multi- and interdisciplinary collaboration, new contributors often remain conservation outsiders, being deeply submerged in their own research areas with regard to their research methods, their view of hierarchy of aims and values of conservation of cultural heritage, etc. Their understanding of targets of input and outcome of their compartmentalized contribution to specific conservation problems might be incompatible with the principles and criteria of modern CCH, thus affecting productivity of such contribution. This paper focuses on this conflict by examining selected relevant aspects based on the experience of the collaborative interdisciplinary research in conservation of cultural heritage.

Colour and space in cultural heritage: Key questions in 3D optical documentation of material culture for conservation, study and preservation

This paper presents an automatic methodology capable of registering non-overlapping laser scans based on a bundle block adjustment for the orientation estimation of synthetic images generated from the 3D data and camera images using a Structure-from-Motion (SfM) method. Adding camera images to the registration of the generated images can improve the block geometry. The SfM process provides accurate image orientations and sparse point clouds, initially in an arbitrary model space. This enables an implicit determination of the 3D-to-3D correspondences between the sparse points and the laser data then, the Helmert transformation is introduced and its parameters are computed. This results in registering the non-overlapping scans, since the relative orientations between the generated images are determined at the SfM step and transformed to the absolute coordinate system directly. The proposed approach was tested on real case studies and experimental results are shown to demonstrate the effectiveness of the presented method.

Colour and space in cultural heritage

This paper presents an automatic methodology capable of registering non-overlapping laser scans based on a bundle block adjustment for the orientation estimation of synthetic images generated from the 3D data and camera images using a Structure-from-Motion (SfM) method. Adding camera images to the registration of the generated images can improve the block geometry. The SfM process provides accurate image orientations and sparse point clouds, initially in an arbitrary model space. This enables an implicit determination of the 3D-to-3D correspondences between the sparse points and the laser data then, the Helmert transformation is introduced and its parameters are computed. This results in registering the non-overlapping scans, since the relative orientations between the generated images are determined at the SfM step and transformed to the absolute coordinate system directly. The proposed approach was tested on real case studies and experimental results are shown to demonstrate the effectiveness of the presented method.