Optimisation d'un traitement de dechloruration d'objets ferreux par plasmad'hydrogene

Abstract

The method of removing chlorides from archaeological iron objects using hydrogen plasma at low pressure has been studied and improved. To carry out the initial experiments and to limit the use of ancient material, synthetic samples were made from iron powder and corrosion products consisting mainly of akaganeite. The time and the temperature required for the complete removal of the chlorides were determined. It was also possible to demonstrate that magnetite, and iron above 400°C, are the final reaction products of the reduction of akaganeite.     

Radiography of Paper

Abstract

Absorbent materials such as wood, paper and cotton stabilize the atmosphere of show-cases against the relative humidity changes caused by temperature variation and by exchange of air with the surroundings.

There are several exchange processes between the air in the case and the outside air: diffusion through porous COllstruction materials, air flow caused by temperature and pressure changes and airflow by convection in a show-case whose relative humidity differsfrom that of its environment. The air changes about once a day in show-cases made by conventional joinery techniques. The rate of exchange can be reduced to less than five volumes a year by sealing a show-case so that only one small hole is left for pressure equalization. A dust and sulphur dioxide filter can then be fitted to maintain a pure atmosphere within.

In heated rooms without air-conditioning the RH may fall dangerously low in winter. A static method of RH control for a show-case is described. This is a saturated solution of sodium bromide covered by a silicone rubber membrane.     

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

Abstract

Chloride-contaminated archaeological iron is unstable and problematic to store and display within museum collections. Reducing its chloride ion content using aqueous desalination followed by storage in controlled relative humidity offers one treatment option. This study reports a quantitative assessment of chloride extraction by aqueous deoxygenated alkaline desalination solutions from 120 individual archaeological iron nails. The three treatment methods comprised alkaline sulphite solution (0.1 M NaOH/0.05 M Na₂SO₃) at room temperature and at 60°C and sodium hydroxide solution (0.1 M) deoxygenated using a nitrogen gas positive pressure system at room temperature. Chloride extraction was monitored using a specific ion meter. The nails were digested after treatment to measure their residual chloride content. A wide range of extraction patterns emerged, with the majority of individual treatments extracting 60–99% of the chloride present. Residual chloride levels for 87% of the objects fell below 1000 ppm and 42% were below 200 ppm. Although no treatment extracted 100% of the chloride in the object, alkaline desalination produced very significant reductions in chloride content. The impact of this on future corrosion of the objects is discussed. This quantitative and statistically viable assessment of deoxygenated desalination treatments provides evidence to support their use in conservation practice, which will impact on procedures for the preservation and management of archaeological heritage.     

Incident preparedness at the National Gallery: Developing a grab bag for rapid response to a corrosive attack

Abstract

Being prepared to address an attack on a painting requires considerable input from both scientific and conservation personnel. When tailoring an appropriate and effective incident response, a well-developed knowledge of the collection, the museum layout, and staffing is also essential. This article discusses the nature of attacks on paintings and the materials and techniques used to mitigate the effects of malicious damage. Previous research into response procedures and the testing of attack substances is also summarized. The primary focus of the article traces the redevelopment of the National Gallery incident response grab bag that caters to various types of attack. Discussions center on developing the customized content of the new bag, material testing, and a practice run-through to establish a response procedure. Ultimately, the practicality and efficacy of the grab bag are demonstrated.     

4 LEAD-TIN YELLOW

Abstract

The proper preparation and application of Paraloid B-72 make it an excellent adhesive for archaeological ceramics and other materials. An understanding of the principles of adhesion is essential to the successful application of solvent adhesives.     

The impact of chloride desalination on the corrosion rate of archaeological iron

Abstract

Although desalination of archaeological iron reduces its chloride concentration and enhances object stability, the reduction in corrosion rate that this produces has never been quantified. This study measures post-treatment corrosion rates in accelerated corrosion environments to identify the impact of removing chloride ions on corrosion rate. Thirty-five archaeological iron nails, treated individually in either alkaline sulphite or nitrogen-deoxygenated sodium hydroxide, were exposed to 75°C and 75% relative humidity together with 31 untreated objects from the same archaeological sites. Object weight change and visual examination of physical change before and after the test period were used to monitor corrosion. 77% of treated objects showed no weight gain and no visible signs of corrosion, while 90% of untreated objects did corrode. The impact of chloride on corrosion of untreated objects was clearly established by a significant linear correlation between chloride content and weight gain. Treated objects with <400 ppm chloride content showed no corrosion behaviour. Corrosion of treated objects was attributed to incomplete treatment: 93% of objects treated to <5 mg/l Cl^? in the final solution bath displayed no corrosion behaviour. Based on these results, desalination of iron objects to enhance their stability offers a valuable option for reducing corrosion rates of archaeological iron, which should increase object lifespan. The results also raise the question of whether low levels of post-treatment residual chloride produce corrosion of any significance. Answering this will be an important step forward for managing the preservation of archaeological iron.     

EDUCATION AND TRAINING OF CONSERVATORS AND RESTORERS

Abstract

In order to test some of the methods of archaeological bronze conservation, a procedure was perfected that reproduces the structure and composition of original patinas. Then the most common methods of treatment were applied on test samples thus prepared and on archaeological items. This experiment has allowed us to choose the best treatment in accordance with the following requirements: restraint of corrosion, speed of operation, lack of colour alteration and avoidance of break-up or solution of patina.     

NOTE ON THE PREPARATION AND MOUNTING OF SAMPLES OF CHALK/GLUE GROUND FROM PAINTINGS FOR SCANNING ELECTRON MICROSCOPY

Abstract

A complete summary of equations for leakage of enclosures is given, including vapour diffusion through still air in openings, and infiltration of air/vapour/particulate mixture. Stack pressure due to temperature and relative humidity difference drives most infiltration. Experiments confirmed the diffusion and infiltration equations for small and medium-size enclosures. Leakage for a carefully made display case with ordinary materials has been reduced to the microbarometric limit of about 0·03 of an air change per day. Simplified tables and charts of leakage are given for 0·1, 1·0 and 10m enclosures, as a function of crack width, hole width, and wall permeability.     

Calcium Carbonate on Bronze Finds

Abstract

The removal of calcareous accretions from archaeological bronzes can be a difficult step in their conservation. Chemical cleaning with chelating agents might be an alternative to mechanical methods. In this study the use of the chelating agent sodium tripolyphosphate (STPP) was examined to determine whether it is effective in discriminating between calcium carbonate and copper patina, and non-corrosive to copper alloys in the presence of air. Comparative experiments with STPP and disodium ethylenediamine-tetraacetate (Na₂-EDTA) were carried out on synthetic malachite, cuprite, calcium carbonate, naturally polished malachite surfaces and sheets of bronze and brass. In addition to the properties of the chelating agent, the solubility of the salts and the pH values of the solutions are crucial factors in the removal of compounds of low solubility. The quantity of metal ions dissolved, estimated by atomic absorption spectral analysis and scanning electron microscopy, showed that the calcareous accretions could be removed satisfactorily, but STPP also dissolved constituent parts of the patina, such as malachite and cuprite, and may harm bronze or brass. Compared to Na₂-EDTA, STPP is less effective in dissolving calcium carbonate. It is less harmful to the patina and base metal, but may lead to patination of the underlying metal.     

A Revised Endpoint for Ceramics Desalination at the Archaeological Site of Gordion,Turkey

Summary

At the archaeological site of Gordion, Turkey, all registered ceramics are routinely desalinated. The standard desalination treatment was investigated by the author with a view to minimizing damage to the ceramics, as well as the amount of water used and the time taken for desalination. An equation that standardizes conductivity measurements in disparate desalination situations is presented. A series of experiments was performed to clarify the behavior of salts at Gordion. Two variables which directly affect the amount of water needed for desalination were considered: the frequency of water changes and the weight-to-volume ratio. The experimental results were compared to on-site experience, and a revised endpoint for desalination is proposed.     

Changing research trends in the field of archaeological wood at the Conservation Department,Faculty of Archaeology,Cairo University

Abstract

Since 1980, much research in the field of treatment and conservation of archaeological wood has been carried out at the Conservation Department, Faculty of Archaeology, Cairo University. Materials and methods used in conservation have been changing gradually over the years worldwide. It was necessary to study critically previous masters and doctoral dissertations on Egyptian archaeological and historic wood, all written in Arabic. This review of them includes a brief history of the Conservation Department at Cairo University and five main focal points of past research: types of wood used throughout Egyptian history, assessment of wood decay, wood properties and composition, treatment and conservation of decorated wood, and the evaluation of chemicals and polymers used in the treatment of archaeological wood and composite objects containing wood.     

Free Expression in Cyberspace-and Libraries

ABSTRACT

Current case law on free speech is a mixed bag. In a case recently dismissed, a professor challenged the President of the University of Oklahoma's decision to bar access to sex news groups from computers on campus. The end result was a two-tier lab system, one permitting access to faculty and those with valid research needs and a second that denied access. On the other hand, a superior court judge ruled that a Cal-State Northridge student could use a Web page to attack an incumbent state senator. Clearer answers will depend on more cases.     

THE DISCOVERY AND CONSERVATION OF AN ANCIENT EGYPTIAN LINEN TUNIC

Abstract

The archaeological evidence for dating a linen tunic found amongst other pieces from the Petrie Museum of Egyptian Archaeology, UCL, is weighed against the evidence from Carbon-14 dating. An account of the structure, conservation and mounting of the tunic is then given.     

The application of vapour-permeable synthetic membranes to the climatic stabilization of museum showcases

Abstract

This paper describes a novel technique to stabilize the relative humidity (RH) of the air inside museum showcases by using a synthetic hydrophobic membrane coupled with a hygroscopic solution in a membrane contactor. RH-monitoring data for two identical test cases, one of them controlled by a set-up with a plane-plate membrane contactor crossed by forced air and lithium chloride (LiCl) solution flows, show a significant stabilizing effect on RH fluctuations. A theoretical model permits forecasts in close agreement with the experimental RH data. Further calculations carried out over a one-year period show that notable damping of external RH variations can be obtained by using a low air circulation rate, small membrane surface area and low solution mass per unit case volume. A more general analytical solution in harmonic conditions is derived and discussed.     

Taking Paint Samples for Pigment Analysis in Nineteenth-Century England

ABSTRACT

During the nineteenth century, chemists became increasingly engaged in the conservation treatment of polychrome surfaces. While collaborations between chemists and museum workers in charge of easel painting collections were mostly oriented towards the improvement of conservation practices, the involvement of chemists in the nascent field of archaeology was oriented towards material characterization, such as pigment analysis of polychrome surfaces. Since this type of analysis is destructive and damages the artwork, it could, therefore, be assumed that chemists were in these cases less concerned with the conservation of objects with an archaeological and historical provenance. On the contrary, my new reading of nineteenth-century English primary sources reporting pigment analysis shows that chemists also had ethical concerns about the physical integrity of archaeological objects and their conservation. This is apparent in the process in which paint samples were taken from the artworks for their subsequent analysis.     

Models for Chloride Ion Diffusion in Archaeological Iron

Summary

The rate at which chloride ions diffuse from archaeological iron into a treatment solution depends on how the chloride ions are initially distributed in the corrosion layer. This paper compares solutions of the diffusion equation for two limiting cases: (1) where the chloride ions are initially spread uniformly through the corrosion layer; and (2) where the chloride ions are initially concentrated at the interface between the iron and the corrosion layer. Although the first model has been used in the past to describe chloride ions diffusing from marine iron, the second is more appropriate in cases where corrosion has drawn chloride ions toward the iron surface. Because diffusion processes in archaeological iron are complicated, the limitations of both these models are discussed.     

Fabrication of an Ultrasonic Nebulizer: Rate of Flow and Performance Studies

ABSTRACT

This article describes how to build, in-house, a new type of ultrasonic nebulizer and presents the results of tests to determine its rate of aqueous flow and its performance during the transport of a collagen-based adhesive (ratio of adhesive actually delivered to adhesive misted). It also reports on a consolidation treatment case study carried out with the new ultrasonic misting prototype: the NebulA-MG 14. This case study was applied to powdery paint layers of a medium-sized oil painting on canvas, 111.5?×?86.5?cm. The new device is shown to be both reliable and effective, particularly for consolidating medium and large-sized works.     

Time pressure: An unexamined issue in organizational newcomers' role development

Although the impact of time pressure on integrative problem solving has been widely explored in traditional negotiation research, little attention has been paid to its effect as organizational newcomers negotiate and coordinate work role expectations with supervisors. This study examines the effect of time pressure on three integrative communication dimensions of supervisory role negotiations: directness, elaboration, and mutual concessions. One hundred seventy employed college undergraduates completed survey items pertaining to recalled supervisory discussions of role expectations. Consistent with the hypotheses, time pressure had a significant positive effect on each of the communicative dimensions of the recalled negotiation.     

STORAGE OF ARCHAEOLOGICAL TEXTILE FINDS IN SEALED BOXES

Abstract

A white deposit was observed on the glass lids of boxes used to store archaeological textile fragments for some 40 years. It was identified as sodium formate formed from formaldehyde given off by cardboard in the boxes. Heavy metal ions in some samples of the deposit originated, via the textile fragments, from corroded bronze ornaments in the graves.     

Stability of treated archaeological iron: an assessment

Abstract

Various desalination methods had been used in the past to treat a large collection of archaeological iron objects. In order to establish whether desalination treatments had been effective, the condition of the objects was assessed and the data analyzed using statistical methods. It was found that objects which had been treated using desalination methods were less likely to re-corrode, and the conclusion was that the development of more effective techniques of chloride removal would be useful.