M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)
Analysis - HEGEDŰS Zoltán: Conclusions of metallographic tests on the production methods of bronze articles and slags
The source of metallic iron in several copper lumps from the Bronze Age is the iron ore used as slag flux material [2]. An example of this is presented by the iron contents of 4.10 mass% and 2.50 mass% of two analysed copper fractions from the finding of Nagy kálló [3], and by the 4.25 mass% of a bronze fraction. Bronze slags of Visegrád On the occasion of the excavations of Visegrád a great quantity of mediaeval bronze slag turned up. By reason of the external appearance of these slag findings they can be placed in various categories. One of the rarer types of them consisted of partly reduced ore remains, charcoal, slag and metal, or rather, the metallic, slaggy part turned progressively into the smelted metal. A fraction taken from the slag was very inhomogeneous and contained ore, charcoal and metal drops alike, and so it proved unsuitable for an investigation in respect of chemical composition. Moving outwards from the charcoal inclusions which contained a metallic and only partially liquified surface towards to the metal melt, the microstructure of the slags continuously changed into the melted metal. Photo 1 shows the structure of the part of the slag near the free surface . On this part of the surface are dark grey (on the picture mainly black) crystals of tin ore (Sn0 2 ) among light grey crystals (CuO), respectively among grains having clearer grey and round enclaves (Cu0 2 ) (unetched, N = 200x). In some grains the lamellar structure of tin ore can still be identified. The texture is complicated in the zone of the initial melting (Photo 2): metallic copper (partly bronze), partly reduced Cu 2 0 (porous, or rather enclaves like Chinese script) and dark-grey-black SnO are visible. On more places of the boundary of the Sn0 2 tighter grey oxide inclusions were formed (unetched, N = lOOx). The structure pattern of the fully reduced bronze is an a-crystal, which is characteristic of tin bronzes, and there are many a + 5 eutectoids, too. Many oxide inclusions are visible in the a eutectoids, and in the region of the a + 5 eutectoids. The textures of the two investigated slags indicate that they are not products of traditional bronze melting. The operations of traditional bronze making are — copper smelting — tin smelting — copper-tin alloying. In this case an attempt must have been made with another process, which consisted in melting and smelting-out copper ore + tin ore contemporaneously (a single-step bronze making). However, the trial was unsuccessful, the reduction of the ore mixture was unsatisfactory, the recovery of tin very bad, and because of the many oxide inclusions also the shape-filling capability was questionable. The investigated type of slag was presumably a product of an unsuccessful attempt. An indication for this is the fact that the slag, found in a great quantity, was the common type of slag of the traditional bronze alloying. Metallographical teachings of iron slags Structure investigation of different iron slags A great quantity of iron melting slags came to light during the surveying and exploration of native siderurgical sites [4]. There were 20 different slags from 15 different sites; metallographic-ore microscopic examinations were performed on these.
