Blogs » MEETING OF THE MINDS - Unstable Enamels at The Victoria & Albert Museum - Paper #3

MEETING OF THE MINDS - Unstable Enamels at The Victoria & Albert Museum - Paper #3

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    Curious About How The Conservationists Deal With Unstable Enamels at the Victoria and Albert Museum?




    Come on in for another

    " MEETING OF THE MINDS "- Paper #3

    at the 3rd Biennial Experts' Meeting on Enamel on Metal Conservation - sponsored by the ICOM-CC Enamel Group of the Glass & Ceramics and Metals Working Groups.

    October 8 & 9, 2010

    The Frick Collection - New York City




    Reviewing the Conservation of Unstable Enamels at the Victoria and Albert Museum


    Juanita Navarro 




    During the preparatory week for the new Medieval and Renaissance Galleries at the Victoria and Albert Museum, London, the condition of many unstable enamels was assessed, including basse-tailleenamels on copper. A major concern for the conservators was the damage being caused by previous coatings to the enamels. Conservators treated the enamels for display while searching for ways to solve the underlying problems of the removal of soluble salts and unwanted coatings from crumbling enamel surfaces.



    The new Medieval and Renaissance Galleries at the Victoria and Albert Museum (V&A), London opened at the end of 2009. The project provided an opportunity to conserve several basse-taille enamels on silver and Limoges painted enamels on copper which were chemically unstable, as well as assess their condition and past treatment. For some, this was their second or even third conservation treatment in recent times. When proposing conservation treatments the principle of minimal intervention was uppermost, not only because of the condition of the enamels and the ethical guidelines, but also due to time constraints.


    In its earliest stages chemical instability will appear on the enamel surface as an almost imperceptible bloom or as a smeary coating resulting from soluble salts migrating to the surface.

    Fluctuations in temperature and relative humidity cause more soluble components to migrate and collect on or near the surface, a process that creates tiny fissures in the glass also referred to as crizzling.

    The salts either deliquesce by absorbing moisture from the environment or crystallize in drier conditions. Both liquid and crystals exert pressure in the micro-cracks leading to further fracturing of the glass. As the crizzling progresses, fine enamel flakes detach from the surface. The most unstable enamel colors aredark blue and  mulberry and these are the most problematic areas to treat.

    The deliquesced salts cause the cracks to disappear visually and the translucent enamels to appear more brilliant, however, removing the soluble salts from the surface of an unstable enamel is recommended as the salts are hygroscopic, increase the alkalinity at the surface, and so lead to further degradation.




    Between the 1960s and 1980s coatings were sometimes applied to unstable Limoges painted enamels, either to the whole surface or to the degraded areas only. The aim of the coatings was to consolidate the enamel surfaces and to provide a barrier layer against environmental fluctuations, thereby stopping or slowing down ongoing degradation of the enamel and the metal substrate.


    Objects with champlevéand basse-taille enamels have large areas of exposed metal, which was often coated to prevent corrosion. Unfortunately, the coating was sometimes applied to the enamel surface as well. The specific coatings used are not always known.

    Early Metals Conservation records at the V & A from the 1970s, show that acrylic resins, such as Incralac  (which contains benzotriazole and used on silver and silver-gilt) and cellulose nitrate lacquers, such as Ercalene and Frigilene, have been used in the past. Test coatings, such as wax (1987), are known to have been applied to unstable enamels but documentation is incomplete. One coating was analyzed (1972) at the National Gallery, London, and found to be polyvinyl acetate.


    Conservation documentation for one plaque (1999) stated that the coating on a Limoges painted enamel appeared to be water-soluble. These coatings, however, failed to provide the protection that was originally intended because they create microclimates which promote degradation processes underneath. Currently more attention is being given to improving the display and storage conditions of the enamels. Today the only lacquer in regular use at the V & A is Frigilene, used on silver and silver-gilt and never allowed to coat any of the enameled areas. Meanwhile, conservators have to deal with the results of past conservation treatments, where severely disrupted surfaces provide the most challenging problems.






    The condition of the enamels treated and of the coatings present varied considerably and the conservation method was selected.

    Treatments were carried out using binocular magnifiers or a microscope. When a brush was used to apply solvents, particularly mixtures containing water, absorbent paper was used to remove as much moisture as possible before touching the surface of the enamel. One Limoges painted enamel had a thick glossy coating over the front and back, giving the surface an unpleasant and misleading appearance. Salts on the blue and mulberry enamels were growing through the coating, which appeared to have changed little since its application and was thoroughly adhered to the enamel. It was possible to sweep the crystallized salts with a sable brush to a sound area where they could be removed with a micro-vacuum, however the coating was retained.


    Several enamels have more problematic coatings, such as 22 small insets of basse-taille on silver on an altar cross (ca. 1470-1490, Florence, 49 x 33.5 cm, M.580-1910). Again, the blue and mulberry enamels were unstable. The plaques had a very unsightly appearance as the coatings (polyurethane) had lifted in many areas; there were large amounts of salts that had deliquesced under the coating. The coating could be removed, but not without removing some tiny flakes from the surface. Loose corrosion products were removed by aspiration with a miniature vacuum tweezer unit or with a dampened sable brush when liquid. Minimal local consolidation was necessary to severely disrupted areas using a weak solution of acrylic resin.


    The Master of the Louis XII Triptych (ca. 1498 – 1512, Limoges, 44 x 45 cm, 552-1877) comprises nine painted enamel plaques, all of which were unstable, but the main three panels showed the most disrupted blue enamel observed so far. Crystallized salts were growing through the sugary mixture, which also contained the remains of a previous coating or consolidant. In a few spots, the salt growth extended from the blue to the neighboring stable white enamel causing damage to those areas. It was no longer possible in some areas to remove dry salts by aspiration with a micro-vacuum as this would remove unacceptable amounts of loose original material. The acrylic consolidant applied in 1999 was reactivated with minimal amounts of organic solvent. Small spots had further applications of dilute acrylic resin as a consolidant only where absolutely necessary to support loose flakes. Although the appearance has improved slightly, the underlying problem has not been tackled and the soluble salts remain in place.




    There will never be easy solutions for the complex problems encountered in the treatment of unstable enamels. It will always be necessary to make decisions on an individual basis for each object.

    Fortunately, conservation has developed to a culture of sharing information that has enable improvement in current techniques, and there is far more practical and scientific information available than ever before to assist in treatment decisions.




    Juanita Navarro, Senior Conservator

    Ceramics and Glass Conservation, Victoria and Albert Museum, Cromwell Road, London SW7 2RL, UK


    Ms. Navarro specializes in the study and treatment of ceramics and glass, and earned a BA in Fine Art before training in Conservation of Ceramics and Related Materials at West Dean College, Great Britain.

    After several years as a freelance conservator, she returned to West Dean for three years as a part-time Assistant Tutor. In 1992, she joined the staff of the Victoria and Albert Museum.

    Her research focuses on the 17th century enameling technique of email en résille sur verre.