2, 615-624 1. Introduction the Method of Precision Casting by Applying
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Arch. Metall. Mater. 63 (2018), 2, 615-624 DOI: 10.24425/122385 A. GARBACZ-KLEMPKA*, J.S. SUCHY*, Z. KWAK*, T. TOKARSKI**, R. KLEMPKA***, T. STOLARCZYK**** STUDY OF INVESTMENT CASTING TECHNOLOGY FROM BRONZE AGE. CASTING WORKSHOP IN GRZYBIANY (SOUTHWEST POLAND) Investment casting technology that utilizes lost-wax casting is one of the most-important achievements of ancient society. In Lower Silesia, Poland (Grzybiany, Legnica county), a 7-6 BC casting workshop was discovered with numerous artifacts, confirm- ing the existence of the manufacturing process of metal ornaments using ceramic molds. The paper presents the research of molds and casts from the Bronze and Early Iron Ages. Microscopic analyses of the cast- ing molds were performed, along with radiographic and chemical composition tests of the artifacts (the latter employing the use of the X-ray fluorescence spectroscopy method). The clustering method was used for alloy classification. The microstructure was analyzed by means of Scanning Electron Microscopy with Energy Dispersive Spectroscopy. Conclusions from the research were utilized in further experiments. Keywords: archeometallurgy, copper alloys, investment casting technology, lost-wax casting, x-ray spectroscopy 1. Introduction Loam molds were generally broken up after pouring. Hence, if the loam molds were well-prepared and used to prepare a cast- The method of precision casting by applying lost-wax cast- ing, it is rare to find them intact at archeological sites. ing is one of the most-revolutionary achievements in ancient The investment casting technology is still important nowa- technology; in fact, it has been successfully utilized through days. It is still used in the automotive, aviation, military and, the present day. The lost-wax casting technique significantly medical industries as well as in jewelry and artistic casting [2-7]. influenced the development of civilizations and helped popular- One of the oldest archeological sites where typical lost-wax ize metal artifacts. casting molds have been found is Tell edh-Dhiba’I, Iraq (located Implementation of the lost-wax casting technique was an in the suburbs of Baghdad) dating to the first half of the second important step in the development of casting technology [1]. millennium BC [8-13]. However, the process of lost-wax casting By using the lost-wax casting technique with ceramic molds, had already been developed in Mesopotamia at about 2500 BC; it became possible to make the molds small yet complex in that is, at least 900 years before the mold from Tell edh-Dhiba’i shape. It enabled the casting of complicated decorative orna- was created [12]. ments, more-massive bracelets, necklaces, and greaves (as A clay mold indicating the application of the lost-wax well as tools). The process started with shaping the model in method was found in Poliochni at the site connected to metal wax, which was then covered in clay and dried; the wax was working, on Lemnos Island (in the Aegean Sea) [12,14-16]. The then melted, and the mold was fired. The mold was filled with mold was prepared for the casting of an axe head; however, it liquid metal and then broken to pieces. An improvement of this was not used due to it being damaged. This mold is about 1000 procedure was the lost-wax technique used for casts that were years older than the Tell edh-Dhiba’i one; therefore, it seems empty inside, with a clay core imitating the inside shape of the to represent an earlier tradition of using the lost-wax method cast. This clay core was covered with a wax layer, whose outside [12,17-18]. shape (after firing and breaking the clay mold) mirrored the Older metal objects made with the lost-wax technique come surface of the cast with its artistic three-dimensional reliefs and from the collection discovered in the Nahal Mishmar cave in ornaments. the Judah Desert near the Dead Sea. The dating of the copper artifacts places their manufacture at about 3700 BC [19-20]. The * AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, FACULTY OF FOUNDRY ENGINEERING, HISTORICAL LAYERS RESEARCH CENTRE, REYMONTA 23 STR., 30-059 KRAKOW, POLAND ** AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, ACADEMIC CENTER FOR MATERIALS AND NANOTECHNOLOGY, MICKIEWICZA 30 AVE., 30-059 KRAKOW, POLAND *** AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, FACULTY OF ELECTRICAL ENGINEERING, AUTOMATICS, COMPUTER SCIENCE AND BIOMEDICAL ENGINEERING, MICKIEWICZA 30 AVE., 30-059 KRAKOW, POLAND. **** COPPER MUSEUM, PARTYZANTOW 3 STR., 59-220 LEGNICA, POLAND. # Corresponding author: [email protected] 616 hoard contained 416 objects made of pure copper, antimony- cause of mold damage was their cracking during the drying stage, and arsenic-rich copper, and nickel-arsenic copper. Some of the wax melting, and especially during the mold firing. Manufactur- artifacts could have been cast by the precision casting method ing technology of the ceramic materials was analyzed based on in expendable molds by lost-wax casting over a stone core their thermal characteristics. It was assessed that, after prelimi- [12,18,21] (analogous to the casts from Shiqmim in the northern nary heating (which was aimed at removing the wax model), the part of the Negev Desert) [17]. mold was fired at 850°C [24]. Copper alloy amulets from Mehrgarh, a Neolithic settle- These artifacts connected with the functioning of the casting ment belonging to the civilization of the Indus valley in today’s workshop in Grzybiany have been researched by an interdisci- Balohistan in Pakistan, come from 5000 BC. Metallographic tests plinary team at the Faculty of Foundry Engineering of AGH show that the ornaments were cast using the lost-wax method University of Science and Technology in Krakow, in cooperation from a copper alloy with the addition of lead [12,22]. Therefore, with the Copper Museum in Legnica and Institute of Archeology Mehrgarh might be the place where the development of lost-wax at the University of Wroclaw [25-27]. technology started. The archeological site connected with the workshop in There have been archeological sites researched in Poland Grzybiany (Site 3, Kunice muni., Legnica county) is situated on that include casting workshops where the lost-wax process was the promontory of Lake Koskowickie in Lower Silesia (Fig. 2). applied, coming from the second millennium BC [23]. Archeological excavations were conducted during the periods of Study of a workshop dating back to the Hallstatt C period 1959-1962, 1970-1973, 1977-1980, and 2010-2011. An analy- (from the seventh to mid-sixth century BC) that was function- sis of the portable artifacts showed that the second level of the ing in Lower Silesia, Poland, indicates a common knowledge settlement should be dated to the Ha C period; that is, from the of los t-wax casting [24-26]. The local casting manufacturing seventh to mid-sixth century BC. However, in the layer related was comprised of mold technology, alloy melting, and casting to the metallurgical workshop, there were artifacts with both sites characteristic of the manufacturing technology of that time. older and younger features than from Ha C. From this settlement in Grzybiany comes rich research material consisting of ceramic casting molds assessed to be the biggest collection of molds for the manufacture of bracelet and necklace in Poland. Alongside, there were also metal artifacts and other objects discovered in the workshop area that were connected to the foundry process; namely, ladles and tuyeres [24,27]. In the workshop vicinity, the main findings consist of fragments of ceramic molds used in the production of band or hoop ornaments. Apart from these, some metal antiques were discovered that were indirectly related to the local casting manufacturing and products directly related to it, like the cast- ing spoon (Fig. 1). Fig. 1. Casting spoon from Grzybiany workshop Application of the wax-model casting technology for the local production of ornaments has also been confirmed by find- ings at other excavation sites in the Silesia, Greater Poland, Kuyawia, and Eastern Pomerania regions [28]. Fig. 2. Location of Grzybiany site in SW Poland and numerical ter- The mold-preparation technology for the lost-wax process rain model of Grzybiany site and its vicinity. Source: ISOK project, was complex and consisted of many stages. The most-common CODGiK. Developed by P. Rajski, T. Stolarczyk 617 2. Research methodology any belong to dispensable forms, destroyed after the mold was filled in order to pull out the ready artifact (Fig. 3). The molds The collection of casting molds and metal artifacts from were made of clay and sand with variable granularity. Organic Grzybiany settlement was investigated. The material was materials were also likely used for mold making but were later submitted to the following non-destructive tests: macro- and burned-out in the process of drying and firing the molds, leaving micro-observations, assessment of the chemical composition, porosities (which facilitated the release of gases from the mold). and defectoscopic tests. The clustering method was used for If this release of gases is obstructed, it causes casting defects in alloy classification. the artifacts such as pinholes visible on the surface or shrinkage The observations were conducted to document the structures porosities inside the casts. The lack of repeatability of most of and surfaces of the ceramic and metal artifacts. Phase content of the mold dimensions as well as their flat and even back sides the casting molds was confirmed by means of X-ray diffraction indicate that the molds were shaped by hand on a flat surface. (XRD) analysis. The quantitative determination of the elemental The sides of the different molds have variable thickness (from composition of the artifacts was performed by X-ray fluorescence 3.5 to 16 mm), but their bottom sides (where the surface is flat) spectrometry with a Spectro Midex spectrometer with energy- are noticeably similar to each other.