Conservation around the Millennium (Hungarian National Museum, 2001)
Pages - 126
1. The surface of a thread sample from an Italian textile fragment from the 15th century. Fragmented, corroded metal foil can be seen on the surface of the membrane. Scanning electron-micrograph.1 Marker: 0.001 mm. 2. A metal-coated strip from a piece of embroidery from the Far East. Corroded tin foil fragments on paper. Scanning electron-micrograph.2 Marker: 0.1 mm rubbed off from the organic support. Combined silver and some of the gold threads blacken because the silver content of the thin metal coating transforms into black silver sulphide, sometimes into the mixture of silver chloride and silver sulphide or only silver chloride (greyish white), which are the most characteristic corrosion products of silver. In the case of tin coating, tin sulphide develops. The worn, thin metal foil (gilt silver) transformed into corrosion can be seen on the surface of the organic support (in this case animal membrane) in picture 1. The picture was taken by a scanning electron microscope, in high magnification. Picture 2 shows a deteriorated, corroded paper surface covered with tin foil in a high magnification. In the case of leather, paper and membrane silver threads, the whole amount of metal covering the organic support transforms into corrosion products. The same happens in the case of tinned paper strips. In the case of membrane and sometimes also of paper coated with gilt silver foil, the extremely thin gold layer is usually worn off by use, and only the compounds of the underlying silver cover the organic support. When gold survives, the corrosion product of silver develops on the surface of the gold layer and nearly totally covers it. POSSIBILITIES TO DETERMINE THE "ORIGINAL" COLOUR OF THE METAL SURFACES The description of the metal thread and the determination of the original colour of the metal are sometimes possible in the case of a blackened metal layer with the thorough scrutiny of the textile or with its examination under a microscope. In protected places, folds, some gold spots may appear, which show the original colour. 126
