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Subject: Studies in Conservation

Studies in Conservation

From: Chandra L. Reedy <clreedy<-a>
Date: Wednesday, April 2, 2014
Volume 59(2) (March 2014) of Studies in Conservation was recently
published and is now being distributed to IIC (International
Institute for Conservation) members and institutional subscribers.
It contains the following six papers:

    "Diagnosis of pathologies in ancient (seventeenth-eighteenth
    centuries) decorative blue-and-white ceramic tiles: Green stains
    in the glazes of a panel depicting Lisbon prior to the 1755
    earthquake"

        Teresa P. Silva
        LNEG-National Laboratory for Energy and Geology, Unity of
        Mineral Resources and Geophysics, Amadora, Portugal

        Maria-Ondina Figueiredo
        LNEG-National Laboratory for Energy and Geology, Unity of
        Mineral Resources and Geophysics, Amadora, and CENIMAT/I3N,
        New University, Lisbon, Portugal

        Maria-Alexandra Barreiros
         LNEG, Unity of Product Engineering, Lisbon, Portugal

        Maria-Isabel Prudencio IST/ITN, Universidade Tecnica de
        Lisboa, Sacavem, Portugal

            Decorative panels of ceramic glazed tiles comprise a
            valuable cultural heritage in Mediterranean countries.
            Their preservation requires the development of a
            systematic scientific approach.  Exposure to an open-air
            environment allows for a large span of deterioration
            effects. Overcoming these effects demands a careful
            identification of involved degradation processes.  Among
            these, the development of micro-organisms and
            concomitant glaze surface staining is a very common
            effect observed in panels manufactured centuries ago.
            This paper describes a study on the nature of green
            stains appearing at the surface of blue-and-white tile
            glazes from a large decorative panel with more than one
            thousand tiles, called Vista de Lisboa that depicts the
            city before the destruction caused by the 1755
            earthquake.  The characterization of green-stained
            blue-and-white tile glazes was performed using
            non-destructive X-ray techniques (diffraction and
            fluorescence spectrometry) by directly irradiating the
            surface of small tile fragments, complemented by a
            destructive scanning electron microscopy (SEM)
            observation of one fragment.  Despite the green
            staining, analytical X-ray data showed that no
            deterioration had occurred irrespective of the blue or
            white color, while complementary SEM-EDX data provided
            chemical evidence of microorganism colonization at the
            stained glaze surface.

    "Identification of white efflorescence on wooden African
    objects"

        Jennifer Poulin, Carole Dignard, Kate Helwig
        Canadian Conservation Institute, Ottawa, Ontario, Canada

            This article describes the investigation of white
            efflorescence on eight wooden African objects from
            Malawi and Zambia and the treatment of the objects to
            remove the deposits.  The source of the efflorescence on
            these objects was determined to be the heartwood from
            which they were carved.  Using gas chromatography-mass
            spectrometry and Fourier transform infrared
            spectrometry, the crystalline efflorescence was found to
            consist of homopterocarpin and pterocarpin, two
            isoflavonoid compounds found in woods and shrubs
            belonging to the genus Pterocarpus, and African Baphida
            nitida.  The crystal growth appeared to be heaviest on
            areas of the objects that were more deeply carved as
            well as on those objects without a surface finish.  The
            storage conditions of the collection were studied and
            found to have likely accelerated the rate and extent of
            the natural movement of the pterocarpan compounds from
            the interior of the heartwood to the outer surfaces.

    "Impacts of consolidation procedures on colour and absorption
    kinetics of carbonate stones"

        A.P. Ferreira Pinto
        Department of Civil Engineering and Architecture, IST,
        Technical University of Lisbon, ICIST, Lisbon, Portugal,

        J. Delgado Rodrigues
        National Laboratory of Civil Engineering, Lisbon, Portugal

            The aim of this research work was to test the influence
            of stone properties, consolidation product, and
            application procedure on the potential harmfulness of
            consolidation on carbonate stones as assessed through
            the impacts on colour and water absorption kinetics.
            This article contributes to understanding the immediate
            and delayed impacts of consolidation treatments through
            the assessment of colour variation and modification of
            water absorption kinetics. The investigation was carried
            out on two limestones having a porosity of 10 and 27%,
            which were treated with three consolidating products
            (ethyl silicate, acrylic, and epoxy resins) using three
            treatment procedures: capillary absorption, brush, and
            full immersion.  All products showed negative impacts at
            different degrees.  We could show that their impact on a
            given stone depends not only on the consolidant type,
            but also on the treatment procedures.  We demonstrated
            this way that the assessment of the potential
            harmfulness of a consolidation treatment for a specific
            intervention should be carried out in conditions as
            similar as possible to those expected to occur in
            practice and should never be based on extrapolations
            made from any other different conditions.  The results
            also contribute to the definition of standard testing
            protocols in stone consolidation, privileging the
            application of a consolidant by direct contact capillary
            absorption when reproducibility is pursued, or by
            brushing when the potential highest impacts on colour
            are the target to evaluate.

    "Use of imaging spectroscopy, fiber optic reflectance
    spectroscopy, and X-ray fluorescence to map and identify
    pigments in illuminated manuscripts"

        John K. Delaney, Paola Ricciardi, Lisha Deming Glinsman,
        Michelle Facini, Mathieu Thoury, Michael Palmer, E. Rene de
        la Rie
        National Gallery of Art, Washington, DC, USA

            A paradigm using multispectral visible and near-infrared
            imaging spectroscopy is presented to semi-automatically
            create unbiased spectral maps that guide the site
            selection for in situ analytical methods (e.g. fiber
            optic reflectance spectroscopy and X-ray fluorescence)
            in order to identify and map pigments in illuminated
            manuscripts.  This approach uses low spectral resolution
            imaging spectroscopy to create maps of areas having the
            same spectral characteristics. This paradigm is
            demonstrated by analysis of the illuminated manuscript
            leaf Christ in Majesty with Twelve Apostles (workshop of
            Pacino di Buonaguida, ca. 1320).  Using this approach
            the primary pigments are mapped and identified as
            azurite, lead-tin yellow, red lead, a red lake (likely
            insect-derived), a copper-containing green, brown iron
            oxide, and lead white.  Moreover, small amounts of
            natural ultramarine were found to be used to enhance the
            blue fields around Christ, and a red lake was used to
            highlight different colors.  These results suggest that
            the proposed paradigm offers an improved approach to the
            comprehensive study of illuminated manuscripts by
            comparison with site-specific analytical methods alone.
            The choice of broad spectral bands proves successful,
            given the limited palette in illuminated manuscripts,
            and permits operation at the low light intensity
            required for examination of manuscripts.

    "Materials and techniques of gilding on a suite of French
    eighteenth-century chairs"

        Raina Chao, Arlen Heginbotham
        Decorative Arts and Sculpture Conservation, J. Paul Getty
        Museum, Los Angeles, CA, USA,

        Lynn Lee, Giacomo Chiari
        Getty Conservation Institute, Los Angeles, CA, USA

            This paper describes the technical study of a suite of
            French Rococo chairs at the J. Paul Getty Museum with
            original eighteenth-century gilding preserved under
            layers of restoration.  A variety of analytical methods
            was employed to identify and characterize the materials
            of the preparatory layers and gold alloys including
            optical microscopy, digital image analysis, polarized
            light microscopy, scanning electron microscopy-energy
            dispersive X-ray spectroscopy (SEM-EDX), Raman
            spectroscopy, and X-ray diffraction (XRD).  The
            materials and techniques were compared with descriptions
            of French eighteenth-century gilding practices in
            contemporary artists' treatises.  Both burnished and
            unburnished original gilding, employing distinctive
            techniques, were found.  The study was particularly
            focused on the gold alloys and the support layer for
            burnished gilding, a mixture known as 'assiette' in
            French and as 'bole' in English.  In addition to the
            original gilded surface, several subsequent campaigns of
            gilding executed with the same eighteenth-century
            techniques were present on the chairs and visually
            indistinguishable from the original gilding.  The alloy
            of the gold leaf used in each campaign was characterized
            through quantitative SEM-EDX via a calibration generated
            from the SEM-EDX data from gold standards.
            Characterization of the gold alloys proved to be a vital
            tool for the interpretation of the layer structure and
            identification of original gilding.

    "Application of colour metallography in the examination of
    ancient metals"

        David A. Scott
        Department of Art History and UCLA/Getty Conservation
        Program, University of California, Los Angeles, CA, USA

            The use of colour in the metallographic examination of
            ancient metals is useful both for research and teaching
            purposes.  Application of different optical methods of
            examination include: polarized light, with or without a
            first-order red compensator, and differential
            interference contrast microscopy (DIC).  The use of DIC
            can be combined with the other techniques mentioned in
            the text for the examination of etched or unetched metal
            surfaces, which are best observed microscopically using
            a metallograph.  Colour techniques are now used
            routinely in industrial metallography, and are available
            for a variety of metals and alloys.  Colour tint etching
            can be used to enhance grain structure or different
            phases present in the metallic artefact which may not be
            visible in conventional etched samples, or which lack
            optical contrast.  Many more applications of these
            techniques in the examination of ancient metals will be
            published in the literature as they become better known
            and second-hand equipment with DIC lenses enter the
            market at a price suitable for conservation laboratories
            to purchase them.

The electronic version of this issue can be accessed by logging onto
the IIC website

    <URL:https://www.iiconservation.org>

as a member, then clicking on Resources/Publications.  Under the
entry for Studies in Conservation, follow the link to Maney Online.

Or, log onto Maney Online directly by going to:

    <URL:http://www.maneyonline.com/loi/sic>

Institutional members may need to refer to their library for
password information.

Chandra L. Reedy
Editor-in-Chief, Studies in Conservation


                                  ***
                  Conservation DistList Instance 27:38
                   Distributed: Sunday, April 6, 2014
                       Message Id: cdl-27-38-007
                                  ***
Received on Wednesday, 2 April, 2014

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