The removal of metal soaps from brass beads on a leather belt

Abstract

Severe corrosion was found covering the brass beads on several beaded belts. The corrosion was a mixture of copper soaps and zinc soaps, and was so thick in some places that it completely buried the brass beads. One of these belts was chosen as a test case for cleaning. The details of the cleaning are described, as are the effects of the corrosion process on the beads and surrounding organic materials. Two supporting studies are also reported: tests of the solubility of the corrosion in a variety of organic solvents, including mixtures of ethanol and petroleum-based solvents; and tests of leather dressings and other coatings on brass, copper, and zinc coupons in various relative humidities (RH), to determine what values of RH could be recommended for storage.     

Pollutants in the Museum Environment - Practical Strategies for Problem Solving in Design,Exhibition and Storage

Abstract

The Oddy test is an 'accelerated' corrosion test employed by museums to evaluate the suitability of materials proposed for use in display and storage cases, The standard Oddy test requires a 28-day test period, and the results are assessed by visual observation. This paper describes an improved test method, which could reduce the length of the test period by half The improved method uses metal films as substitutes for the traditional metal coupons posing as 'surrogate art object', The new test results are then evaluated by computer with digital image processing for more objective selection of less corrosive materials.     

Altération et nettoyage de pièces en argent doré

Abstract

By studying the mechanism of sulphation of silver-gilt objects in relation to the method used for gilding, its thickness and its appearance, it has been possible to develop a procedure for electrolytic treatment. The two-step treatment is carried out in a buffered solution of sodium nitrate and comprises cathodic reduction of the silver-based corrosion products followed by anodic dissolution of the reduced silver. The behaviour of the different materials is described, as well as certain limiting factors.     

ON THE CONSERVATION OF THE BAPTISTERY DOORS IN FLORENCE

Abstract

The causes of deterioration of the gilded bronze doors of the Baptistery in Florence have been examined and the mechanism of corrosion discussed. An apparatus for thermal conditioning has been proposed and tested either on the north door of the Baptistery, or on samples exposed to the urban atmosphere in Milan and by laboratory tests on an electrochemical model. The effectiveness of the proposed apparatus has been verified by weight losses, by assessing soluble salts, by visual observations, by local chemical microanalyses, by morphological examinations with a scanning electron microscope equipped with an X-spectrometer and by X-ray diffraction.     

Method for Stabilization of Leaded Bronzes Affected by Corrosion of Lead

Abstract

To inhibit the corrosion of lead objects and lead in high-lead bronzes, particularly in the presence of organic emanations from wood, paint, etc., and/or high humidity, is a difficult conservation problem. A method to prevent corrosion of lead in copper objects was therefore developed using benzotriazole (BTA). The most appropriate treatment method for the conservation of the objects was to immerse them in neutral BTA solution, for which a 0.5% (w/v) concentration of BTA was enough. For bigger objects, three or four coats of 1.0% solution applied by brushing were equally effective. The method was used successfully for the conservation of some ancient copper coins and bronze sculptures containing high amounts of lead; it can also be used to inhibit corrosion of lead objects.     

STUDY OF GLASS AND GLASS-MAKING PROCESSES AT WADI EL-NATRUN,EGYPT IN THE ROMAN PERIOD 30 B.C. TO 359 A.D.

Abstract

In the Roman period, from about 30 B.C. to about A.D. 359, Wadi el-Natrun was probably one of the main centres of the glass industry in Egypt. In this district, the essential materials for glass-making processes, mainly silica and natron, were and are still quite abundant. Two kinds of crucibles were in use: fritting and melting. The first kind was used for fritting the raw materials of glass to produce glass frit blocks. Such fritting crucibles had a rectangular form which is not usually encountered in other places. Probably this was intended to facilitate the transport of the glass frit blocks produced to glass factories in different places where raw materials were not available. Dimensions for two fritting crucibles are proposed. The body texture is coarse, highly porous and almost loose. These features were intended by the ancient glassmaker to release the frit block easily by fracturing the crucible, which was thus used only once. The chemical composition is distinguished by a high content of iron oxide, lime, magnesia and alkailis, thus decreasing the resistance of the crucible to corrosion. The mineralogical compositfon is mainly: alpha quartz, albite, oligoclase, andesine, diopside, augite and a small amount 01 anorthoclase and other trace minerals. The crucibe material has been found to have been originally made by mixing mud with sand to which an amount of chopped straw was added; after sun-drying the crucible was baked before use. The temperature employed in this process never exceeded 1100°C since, under prolonged heating, the crucible material fuses in the range 1150–1200°C.     

A technical note on the casting of unsupported polymeric films

Abstract

In conducting research on the physical propertIes and durabIlIty of coating materials used in the conservation of art objects, difficulty was encountered In efforts to make uniformly thick, coherent, free-standing films for testing purposes. An efficientrapid casting technique has been developed utilizing reusable molds. The technique is applicable to the preparation of films from a wide range of materials.     

A rapid test for the detection of substances which will tarnish silver

Abstract

A sodium azide based solution decomposes when in contact with materials which have the potential to tarnish silver by evolution of hydrogen sulphide. The rate of evolution of nitrogen gas from the reagent has been used to assess the severity of the tarnishing. The test is microchemical and takes only a few minutes to perform.     

Understanding the gum dichromate process in pictorialist photographs: A literature review and technical study

Abstract

In the late 1800s, pictorialist photographers favored a diversity of photographic techniques, including the gum dichromate process. Sometimes superimposed over other photographic images such as platinum and silver prints, the gum dichromate process utilizes a light-sensitive mixture of gum arabic, pigment, and a potassium dichromate solution hand-applied onto a sheet of paper and exposed to light while in direct contact with a negative. The definitive identification of this process has proven to be a challenge due to many variations and intermingling of techniques used by photographers of this period. This research began with a search through the historic literature, followed by the creation of test samples based on historic recipes, and the X-ray fluorescence analysis of these tests. The identification of pigments and the presence of chromium have been associated with the gum dichromate or other dichromated colloid processes in the past. Research results reveal that the presence of chromium may have more complex sources, requiring a more discriminating approach and a modified protocol for the identification of gum dichromate photographs.     

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.     

Feasibility studies on applying UV-lasers for the removal of superficial deposits from historic glass

Abstract

Feasibility studies on applying laser radiation for the removal of superficial deposits from historic glass are being carried out within a three-year interdisciplinary project in Germany. Previous investigations revealed that there is insufficient knowledge about interaction processes between UV-laser radiation and individual surface layers of encrusted historic glass. Therefore, detailed studies were first carried out on special model glass samples to simulate different stages in the corrosion of historic glass. The potential of UV-lasers for removing crusts and biolayers, as well as layers of various conservation materials (due to previous conservation work) is examined. It is of great importance to avoid damage to materials such as gel layers, paint layers or the glass itself. A KrF-excimer laser operating at λ = 248nm is used for the experiments. A mask projection technique is applied for irradiation. A modified optical set-up has been designed, using cylindrical lenses for large-area removal by 'line scanning'. Removal rates and thresholds for the materials mentioned above are monitored. The collected data enable comparison and evaluation of the feasibility of removing superficial layers from historic glass artifacts. The results indicate that in some cases a closed loop process control will be necessary to avoid over-cleaning.     

Real-time monitoring of indoor air corrosivity in cultural heritage institutions with metallic electrical resistance sensors

Abstract

A system for continuous monitoring of atmospheric corrosivity has been developed. An electronic unit measures and records changes in the electrical resistance of a thin metal track applied on an insulating substrate. If the metal corrodes, the effective cross sectional area of the track decreases and the electrical resistance increases. Sensors made of silver, copper, iron/steel, zinc, lead, tin, aluminium, bronze, and brass at thicknesses from 50 nm to 250 µm were tailored for environments with different corrosivities. The developed technology proved capable of providing high sensitivity, allowing for real-time corrosion monitoring even in low-corrosive indoor cultural heritage facilities. Laboratory tests showed good reproducibility with the standard deviation of parallel measurements at less than ±20% for metals which corrode uniformly in the tested environments. Several examples selected from a broad testing programme in partner museums, libraries, and other institutions show successful applications of the logger system for characterization of air quality control in indoor locations, during transport and in temporary exhibitions; assessment of new buildings and storage facilities; and fundamental studies of optimal conservation and storage procedures. A first outline of a classification system for lead, which is particularly sensitive to the presence of carboxylic acids, is given. The technique has a large potential as an independent method for monitoring air quality in facilities displaying and storing valuable objects of cultural heritage.     

Refinements Introduced in the Oddy Test Methodology

The ‘Oddy test’ is an accelerated corrosion test introduced in the 1970s at the British Museum to identify materials likely to emit volatile substances that could harm museum artefacts. It is carried out in many museums all around the world, but not always using the same methodology, which makes it difficult to compare and share test results between institutions. Refinements to the Oddy test methodology have been implemented at the British Museum over the last decade and the aim of this paper is to present these and promote consistency across institutions. The modifications introduced concern the method used to wash the glassware, the preparation of the metal coupons, and standard methods for preparing samples of liquid coatings, adhesives, and adhesive tapes. Finally, conducting Oddy tests is time consuming and measures employed at the British Museum to reduce the number of materials to be tested and streamline testing are described.     

Addressing challenges with systematic review teams through effective communication: a case report

Background:Every step in the systematic review process has challenges, ranging from resistance by review teams to adherence to standard methodology to low-energy commitment to full participation. These challenges can derail the project and result in significant delays, duplication of work, and failure to complete the review. Communication during the systematic review process is key to ensuring it runs smoothly and is identified as a core competency for librarians involved in systematic reviews.Case Presentation:This case report presents effective communication approaches that our librarians employ to address challenges encountered while working with systematic review teams. The communication strategies we describe engage teams through information, questions, and action items and lead to productive collaborations with publishable systematic reviews.Conclusions:Effective communication with review teams keeps systematic review projects moving forward. The techniques covered in this case study strive to minimize misunderstandings, educate collaborators, and, in our experience, have led to multiple successful collaborations and publications. Librarians working in the systematic review space will recognize these challenges and can adapt these techniques to their own environments.     

The Digital Transformation of Special Collections

ABSTRACT

The effect of digital technology on special collections has been profound and ongoing. The purpose of this article is to explore the effect born digital materials, digitization, and intellectual property have had on special collections in the 21st century. In particular this study will focus on how archival materials have been significantly transformed by interacting with digital technology—providing both challenges in management and opportunities for new online environments to expose this content worldwide. Finally, a research experiment underway at the University of Virginia Library offers a framework that may help highlight some strategies for exploiting new opportunities going forward.     

A review of conservation treatments of waterlogged basketry from the northwest coast of North America

Abstract

Basketry artifacts fabricated from spruce and cedar limb wood and root and the inner bark of yellow and western red cedar have been found in water-saturated archaeological sites in the Pacific Northwest since the mid-twentieth century. These artifacts range in age from a few centuries to more than 5000 years old. While these materials retain their overall physical structure due to burial in an anoxic environment they are degraded on the cellular level. Experiments and treatments performed by archaeologists and conservators over the past 50 years have attempted to stabilize these degraded structures and minimize splitting, crumbing, and distortion of the woven structures as they dried. Many of these tests and treatments are published in out-of-print conference proceedings or remain unpublished in conservation lab records. This review of tests and treatments as well as a current condition assessment of several collections brings this information together for the first time and allows conservators and archaeologists specializing in these treatments to see the broader arch of success and failure of the preservation of waterlogged basketry materials.     

THE USE OF THE AIRBRASIVE PROCESS FOR CLEANING ETHNOLOGICAL MATERIALS

Abstract

Ethnological specimens of many different materials can be dry cleaned mechanically by means of a grit-spraying unit. Plain and painted leather, corroded metal, beadwork, metallic embroidery, wood, ivory, bone, basketry, some paper, pottery, shell, some textiles and stone are items which can be cleaned with less disturbance to the surface than is often occasioned by the use of other methods. A specimen constructed of several materials may be cleaned by this one method rather than by several, thereby also avoiding the use of water, solvents or other chemicals. The powdered abrasives used are calcium magnesium carbonate, sodium bicarbonate, glass beads, and several grades of aluminium oxide. Silicone carbide powder is used occasionally for very hard corrosion products on metal.     

An Investigation of Deterioration of Archaeological Iron

Abstract

A small but significant proportion of the archaeological iron objects in the British Museum collection have been problematic in that some of them have required repeated treatment. The deterioration of iron objects during storage was studied using microscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray analysis, X-ray fluorescence spectroscopy and ion chromatography. A total of 125 iron objects, including 56 from two British Roman sites and 69 from three Anglo-Saxon sites, were studied. Both surface corrosion and corrosion layers on polished cross-sections were investigated. The study revealed that the present condition of the iron objects varies; some are in a stable condition and others have been deteriorating, with pitting and weeping present on the surface. No treatment method had stopped corrosion for every object, although the alkaline sulphite treatment seemed to be more effective than the other methods. The results also showed that chloride ions can be present at the interface of the metal and inner corrosion layers. It is recommended that iron objects which have been mechanically cleaned without desalination treatments are kept in a dry environment to prevent further deterioration.     

Metal corrosion rates in aqueous treatments for waterlogged wood-metal composites

Abstract

Corrosion rates are presented for metals in the aqueous solutions intended for treating both the wood and the metal components of a waterlogged wood-metal composite object. The metals include lead, mild steel, cast iron and the copper alloys of bronze, cast brass and wrought brass. The corrosion rates were determined using a standard weight-loss method in which clean metal surfaces were immersed in the solutions for two months at room temperature. The treatment solutions included Acrysol® G-11O for lead, Witcamine® RAD 1100 for copper alloys and Pluracol® 824 or the corrosion inhibitor Hostacor® KS 1 in PEG 400 for iron. These treatment solutions were prepared in distilled water as well as in a synthetic seawater. For reference, metal corrosion rates were also determined in distilled water, synthetic seawater and PEG 400. The results demonstrate that, in general, clean metal surfaces corrode more slowly in the treatment solutions than in PEG 400 solutions. However, before recommending these solutions for the treatment of composite objects, further testing is needed to determine how effective they are in reducing the corrosion rates of metals covered with a thick corrosion crust, and to see if Acrysol G-110 is capable of bulking and consolidating waterlogged wood.     

Conservation of Plastics: Materials Science,Degradation and Preservation

Abstract

The Ördekli Bath is an important fourteenth-century monument in Bursa, Turkey. The bath partially collapsed during the 1855 earthquakes. The plan, construction techniques and material properties of the bath have been investigated to determine whether they could have been partly responsible for the collapse of the men's frigidarium. In this study, the physical, mechanical and chemical properties of the original materials, sampled from both the stable and unstable parts of the bath, were examined and compared with each other. The test results showed that the building materials used for the bath are incredibly durable. It is therefore proposed that the collapse of the men's frigidarium was not caused by the intrinsic properties of the materials from which the bath was constructed. The collapse is thought to result from flaws in the original design and construction techniques used for the men's frigidarium.