Abstract
This dissertation studies for the first time the history of varnishing and glazing in relation to the use of drying oils in the workshop of the medieval painter until the late sixteenth century. Results from technical research and historical reconstructions will be combined with an analysis of medieval written sources,
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such as encyclopedias, lapidaries, and the numerous recipes that can be found in art technological manuscripts. The spectacular verisimilitude in the paintings of Jan van Eyck (ca. 1390-1441) breaks in a revolutionary way with everything that had been made before his time. In the sixteenth century, Van Eyck's novel way of painting even resulted in the famous story that he invented a drying oil that enabled his remarkable technique. By now we know that this 'invention story' cannot be true, because oil paint had been used since at least the twelfth century. It is true however, that, to make his paintings, Van Eyck exploited a technique that was only possible with oil: glazing. Glazes are thin, translucent paint layers of saturated color that allow light to pass through and finally reflect back through the paint. This way, the painting illuminates itself, as it were, from the inside out. Glazing has a long history and, before Van Eyck, was used mainly to substitute precious materials with paint. Medieval painters for instance, used glazes on metal foil or leaf to imitate the translucent splendor of gemstones, stained glass windows and enamel. Likewise, written sources provide ample evidence of the importance of glazing in relation to the art of making Ersatz. They show for example, that oil was specially prepared to make it more translucent and glossy when ground with certain pigments. Varnishes made with drying oils also need to be studied as an important part of this history of imitation. Next to their protective function, they were employed to give the shine and brilliance of enamel and precious stones to objects made out of paint. When yellow colorants were added, varnishes could even be employed to imitate gold on silver leaf or tin foil. From the 1420s onwards, Jan van Eyck and his contemporaries no longer produced works characterized by Ersatz, but instead used glazes and opaque paint to represent, with meticulous skill, translucent glow and reflective luster. Whereas we might never know the precise nature of Van Eyck's 'secret', with this study we now have a history of the painting technique that helps explain the birth of northern renaissance painting.
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