Budapest Régiségei 18. (1958)

JELENTÉSEK - Duma György: Középkori mázas kerámiák vizsgálata 565-586

II GOLD-PLATED CERAMICS FROM THE 15th CENTURY Several fragments of tiles with a gilded enamel were brought to light in the course of the excavations made from 1946 to 1956 in the Fortress of Buda. Similar objects had been found earlier in the vicinity of the palace at Nyék. The tiles are supposed to have adorned the roofing (cupolas) of the palace of King Matthias. They were probably manufactured in the middle of the 15th century. No similar pieces have been found in Hungary either from earlier or later periods, and we possess reliable knowledge of but one instance of the occurrence of technically similar pieces abroad. The analysis of the gilded tiles under review had a double object : first, to become familiar with the process by which gilded ceramics were manufactured, as also the then technique of gilding ; second, to reproduce these processes on the strength of the proposed investigations. The result of the analyses j ustif ies the assump tion that the gilded ceramics were made of plastic clay which becomes red if burnt, and that they were manufactured by means of the potter's wheel. They probably served as an ornamental ridging on the quondam royal palace. That they were used outdoors is evidenced by the fact that they reveal the symptoms of freezing. In accordance with their function only their outside was glazed and coated with a thin layer of gold. This layer consisted of a gold foil, an alloy of gold, silver and copper. The tiles are covered with a glaze which contains a high amount of lead and becomes smooth only at 940° C, a temperature unusually high for potter's glaze. The entire glazed surface of all pieces used to be overlaid with an unadorned film of gold, many parts of which have since been partially or wholly destroyed. The gilt follows the surface of the enamel in an uneven layer, the thickness of which was found to be between 7 and 25 /u on the sections examined under the microscope. The process of gilding was to fix the gold foils laid on the leaded enamel by means of annealing, a process hitherto unknown in the annals of ceramics! The gold film, a rectangular foil, was laid on the previously glazed tiles with the aid of some ashlessly burning adhesive substance. The annealing of the gold film was performed at a red-heat temperature, i, e. one considerably lower than the melting point (940° C) of the underlying leaded enamel, so that the fixation of the gold film must have taken place after the diffusion of the gold into the enamel by means of a process of reaction in the solid phase. In the present experiments the test pieces, after burning them once, were coated with a glaze, the composition and properties of which (detailed in the paper) were almost identical with the original, and then burnt again in an electric furnace at 940° C. The glazing thus burnt-in was then overlaid with a gold foil by means of resin dissolved in alcohol. The annealing of the gold film was then performed at a lower temperature. A temperature of from 500 to 600° C has been found to be the most appropriate for this purpose. The gilt thus fixed has proved to be identical with the historical one in every respect so that the correctness of our hypothesis regarding the original process of gilding has been confirmed fully by the experiments. CAPTIONS Fig. 1 Fragment of gilded tile with signs of freezing Fig. Fig. 2 Detaching gold layer, dark patches representing underlying glaze, light patches representing still unimpaired parts of gilt Fig. Fig. 3 Crumpled and broken gold film Fig. 4 Magnified part of Fig. 1, revealing rectangular Fig. arrangement of gold layer Fig. 5 The gold film does not suffice to conceal Fig. faultiness of underlying enamel Fig. 6 Small craters well-visible on the surface of glaze not covered with gold Fig. Fig. 7 The edges of the quartz-granules contained Fig. in the basic substance have become indistinct at certain spots, and show the initial symptoms Fig. of disintegration 8 Numerous granules of quartz, and many bubbles contained in the glazed coating ; the dark upper stripe represents the gold layer 9 The part shown in Fig. 8, between crossed Niçois with vividly luminous granules of quartz 10 The glazing vigourously dissolves the basic substance on the tile's edge surface 11 Nearly the entire thickness of the glazing filled with bubbles beneath gold film, near surface 12 Laminar gold layer on the surface of enamel 13 Rough continuous layer of glaze beneath lost gold film 14 Newly glazed and gilded original tile ; thinness of gold layer conspicuous 586