Historical metallurgical activities and environment pollution at the substratum level of the Main Market Square in Krakow

Archaeological research was carried out on the Main Market Square in the years 2005–2010, by the Archaeo-logical Research Group Market Square (Schejbal-Dereń and Dereń, 2010, 2011; Szejbal-Dereń and Garbacz-Klempka, 2010), yielding new discoveries in the field of casting (new types of moulds, etc.). Moreover, the collec-tion of historical objects and materials connected with ornament-making workshops was enlarged: casting cru-cibles, slags, raw materials and casting moulds, which constitute important sources relating directly to gold-smithing activities. Based on the analysed objects, it can be concluded that there were already workshops in the early Middle Ages, where casting techniques were used for the production of body and clothes adornments. Many artefacts were found (both imported and made locally), cast from bronze, copper, tin, lead, silver and gold. The historical artefacts found at the Main Market Square are linked to a broad spectrum of activities, amongst which the ones connected with using metals and alloys for the production of ornaments and everyday objects seem to be especially important. The group of found objects includes numerous cast rings.

These relics come primarily from cultural layers and structures — possibly workshops connected with the early medieval settlement — functioning in the area of the (present day) Main Market Square in the 12^th century and the first half of the 13^th century. Most of the slags, metal (copper and lead) lumps and crucible fragments were found in buildings used for economic purposes — the precise function of which was not determined — but a casting mould was discovered in the utility levels of a dwelling, dated to the first half of the 13th century.

Objects and study area

It should be emphasized that all the material analyzed during the research (i.e. the earth from individual layers of archaeological strata and the deposits from the place where the loaf of lead was found, coming from the trench A, as well as the deposits of the rooms of the Great Weigh House, where metal slags were present) was taken only from those areas where it was possible to clarify dating. The age and diagnosis of the layer stratigraphy was confirmed based on the analysis of historic ceramic material. (Schejbal-Dereń and Dereń, 2010, 2011). The metallic objects from the Great Weigh House have been made available for research by the Archaeological Re-search Team of the Main Market Square.

The Great Weigh House (GWH) was located in the south east part of the Main Market Square and it func-tioned as the Scales Office from about 1300 AD (Komor-owski and Sudacka, 2008). It was a mortared building, with its entrance from the side of St. Wojciech’s Church. The artefact samples come from archaeological layers originating from different parts of this building – GWH (Fig. 1). Layers were sampled, both in this region and also in the neighbouring area at the entrance to Bracka Street – trench A (Fig. 2a–d). The results presented in this article are based on the content analyses of metal artefacts and physicochemical earth markers from the places where the artefacts were discovered. They were collected from an area of archaeological excavations reaching down to a depth of 4 metres below the Main Market Square in Krakow.

The main purpose of the ongoing interdisciplinary re-search is to determine the characteristics of ground envi-ronment changes in the Main Market Square area (see Fig. 1), and to compare these with analyses of metal artefacts found in archaeological layers in the area near the Great Weigh House, which is the historical area where metals were used.

Samples of earth (geoartefacts) and metal artefacts were collected by the authors during archaeological work, making it possible to carry out an interdisciplinary analy-sis of the chemical composition of metal objects and the state of contamination of the site of exploration (Fig. 1, 2). Furthermore — and most importantly — the site of collection had an unequivocal archaeological context. Mini profiles of archaeological layers were collected from the sites of exploration where the artefacts were found (see Fig. 2a–b) (these layers were ascribed heights above the mean sea level using geodesic techniques). In other regions, where sequences of intact layers were present which were dated to the Middle Ages (which were significant for analyses of changes of the degree or spreading of contamination), profiles or a collection of samples (in the direction of run-off) were collected from the bottom to the top (see Fig. 2c–d). The area where the loaf of lead was found was a special place — the lead was sampled with the aim of assessing the degree of contamination of the substrate exposed to prolonged contact with the metal (see Fig. 2).

The present research was aimed at determining the degree and nature of the influence of human metallurgical activities on changes in physicochemical parameters of soil and earth in archaeological strata, especially within production and utility levels. At the present stage of the investigation, the primary objective was to answer the question as to whether, in the Middle Ages, there was a melting shop in the area of the Main Market Square in Krakow, and what kind of effect it had on the earth and sediments.

The historical, copper-based alloy that was analysed is difficult to classify according to present-day norms. The proportions of different components seem to be similar in specific artefacts, but certain items with compositions that are significantly different from median values can be singled out (Table 1, Fig. 3d). And so, with aver-age copper content (%) at 75 and zinc at 16, the percent-age of copper varies from 62.42–88.57 and that of zinc: 10.01–23.46. The tin content (%) is low, on average 3.39, although in one case the percentage of this element exceeds 19.42. The artefacts contain little lead (%) — on average 1.07 (the maximum value is 2.43). There are traces of other elements, namely, arsenic, antimony and silver. The closest modern equivalents to the historical alloys used in Krakow are, according to the CDA (Cop-per Development Association), modern copper-tin-zinc and copper-tin-zinc-lead alloys with the following reference numbers ascribed to them: C84200, C84400, C84410, C84500, and C84800. They belong to the group of brasses, a kind of casting copper used nowadays (Kulig, 2007).

A series of metal analyses of the artefacts from the Main Market Square showed that a typical material used for the rings made in Krakow was an alloy containing about 75.00 ± 0.05% copper, and 15.00 ± 0.01% zinc, with the addition of tin (4.00 ± 0.06%) and lead (1.00 ± 0.05%), and with traces of antimony, arsenic and silver (Ag 0.10 ± 0.01%), the latter elements being impurities remaining from the smelting of copper from ore. This material is sometimes referred to as artistic bronze, although in the technical literature it is called brass – with a colour that is close to gold. Apart from its aesthetic value, it also has very good casting properties, which must have been known to the craftsmen of old. Despite metallic zinc not being known at the time, it was obtained by melting pure copper with zinc ore, which was de-scribed precisely by Monk Teophile in the 12th century (‘...stone of yellowish colour and sometimes red, which is called (…) calamine, is mixed next with very fine coal and addition of copper … this mixture is called brass.’). An analysis of guild documents indirectly points to the kinds of materials used by particular metal guilds in Kra-kow, but their precise characteristics can only be deter-mined by thorough research (Garbacz-Klempka et al., 2015; Szejbal-Dereń and Garbacz-Klempka, 2010).

The most numerous group in a series of historical rings from the Main Market Square was made from cop-per alloys. From the technological point of view, this kind of alloy has better qualities than pure copper. The presence of zinc in the alloy lowers its melting point, which creates better conditions for carrying out melting, and facilitates its working in the craftsman’s shop. The main advantages of brass are its ease of working (including chasing and polishing) and soldering. It is hard to overestimate its aesthetic values: its colour and lustre after polishing. It is also resistant to corrosion. This technique made it possible to create ornamental items with complicated shapes, using clay or stone moulds. As a result of archaeological excavations at the Main Market Square, casting crucibles and fragments of three stone casting moulds, including one used for ring making, were found (see Fig. 3a–c). The results of specialist analysis of medieval ornaments from the Main Market Square attest-ed to the use of the casting method for producing these artefacts in the early medieval period.

Archaeological analysis of historical material allowed for more precise dating of the metal artefacts (a sample from Room R of the Great Scales, sample R3 from layer 109) to the turn of the fourteenth and fifteenth centuries. However, ongoing archaeological research does not rule out that the material was created in the late fifteenth century.

Because the structure of the investigated slag samples (metallurgical semi-finished products) revealed the presence of charcoal, they can be used for dating. Thus, the time horizon of the 109 layer can be verified, from which the earth sample (RCu and RPb) came. Among a number of metal artefacts to determine the age by analysis of the radiocarbon age, one object R3 was selected. It was representative of a large group of the finds collected by the Archaeological Research Team of the Main Market Square.

The result of radiocarbon dating 295 ± 30 BP after calibration gives the range of 1490–1660 cal AD (2σ = 95.4% confidence interval) or 1520–1650 cal AD (1σ = 68.2% confidence interval). The calibration results indi-cate, therefore, that the slag and the formation of the 109 layer in room R should be attributed to 16–17^th century. According to written sources, it was the period of most intense activity of Great Scales, the functioning of the lead depot in the House of Lead near the Great Weigh House that survived until the Swedish “deluge”.

At places metal constituents penetrated into the well preserved structure of the wood cell walls (see Fig. 4). Charcoal was a basic fuel in metallurgy, both in copper smelting and in recovering metallic components, such as silver, from copper. Coal became part of the slag structure, so its presence should be connected with metallurgical processes. The above findings may therefore indicate that as late as in the 17^th century there was a melting shop on the Market, which, due to its production volume could be considered as metalworks. Because of the presence of slag and metal scraps the impact of its operation is “stamped” on historical layers in the area near GWH, and trench A, which maybe was the main lead storeroom. As a result of different migration forms, contaminants are also observed throughout the Old Krakow area.

Earth samples from room R, from layer 109, were analysed for Pb and Cu (%) and average concentrations were extremely high: 12.84 ± 0.54; 10.86 ± 0.22 (sample RCu) and 16.51 ± 0.57; 0.73 ± 0.01 (sample RPb). Aver-age concentrations (g/kg) of Pb at the level of 3.10 ± 0.21, and Cu at the level of 0.22 ± 0.01 were determined for a sample from another room. These significantly exceeded both the values of the local geochemical background, which are Pb: 8–25 and Cu: 2–30, and the legally prescribed limit values for soil and earth (above which they are considered to be contaminated), which are for Pb — 100 and Cu — 70, and also the environmental standards for water sediments (including residues extract-ed from dredging water reservoirs), where the values are Pb — 200, and Cu — 150 (Kabata-Pendias and Mukher-jee, 2007).

The earth layers which yielded all the artefacts came from the Great Weigh House area and the neighbouring trench A, and they were characterised by greatly varying values of physico-chemical markers. Moisture fell within the range 0.981–29.672 (wt%) and loss on ignition representing the organic substance content ranged from 0.573 to 9.900 (wt%). The content of fluorides in water extracts (1:3), which represents the content of easily soluble salts, was between 0.3–3.9 (mg/l); for chlorides it was 24.5–495.0; for nitrates: 0.7– 201.5; for phosphates: 0.01–6.10; and for sulphates: 5.6–233.0. The salinity of most of the samples exceeded 1.00 mS/cm, reaching up to 3.00 mS/cm. The ground was characterised by active acidity within the pH range 6.23–7.30. In samples ob-tained from both places, the grain-size fraction (0.18– 1 mm and | 0.18 mm) dominated, usually totalling over 75 wt%.

Geochemical research on the Main Market Square and many others areas was aimed at emphasizing the role of metals as markers in archaeology, with the lead and cop-per content in the historical grounds being recognised as especially relevant. The artefacts analysed were highly corroded cakes of copper or archaeological objects of another kind with a porous structure (see photos in Fig. 1). Chemical analysis of the metal artefacts found in the layers of the excavated part of the Great Weigh House (see Figs. 1, 2 and 5), in room R, showed predominant copper content (Fig. 5e). In another room (labelled W), some of the artefacts showed a higher content of lead than copper (Fig. 5f).

The earth forming the strata on the eastern side of the Main Market Square, not being directly influenced by the functioning of the Great Weigh, contained (mg/kg): Cd — 2.0 ± 0.2, Cr — 17.5 ± 1.0, Ni — 7.3 ± 1.0, Cu — 80.4 ± 4.0, Pb — 291 ± 20, Zn — 82.9 ± 7.0, Mn — 412 ± 38 and Fe (%) — 1.69 ± 0.10 (average values from about 50 samples, 5 profiles). On the opposite side of the Cloth Hall, in the western part of the Main Market Square, the average concentration values in mg/kg were (based on 45 samples,7 profiles): Cd — 1.63 ± 0.15, Cr — 12.5 ± 1.0, Ni — 8.5 ± 0.8, Cu — 54.92 ± 2.00, Pb — 301 ± 10, Zn — 81.7 ± 6.0 Mn — 102.0 ± 9.0, and Fe (%) — 0.53 ± 0.04 (see Fig. 1).

Analysis of these results shows that, with the exception of Cu and Pb, the determined metals do not exceed environmental standards for soil and earth. Hence, when researching strata material from the Great Weigh House areas and trench A, special attention was paid to these elements, assuming that the main causal activity was the processing of Cu and Pb and its conversion into marketa-ble portions. Because of higher Ni concentrations, this element was also included. In the chart (Fig. 5d), the concentration changes are presented in the order in which the samples were obtained from the Great Weigh House areas and from the neighbouring trench A, located at the exit of Bracka St.

It can be clearly seen that, generally speaking, within Trench A, the strata are less contaminated with Cu and Pb than in the case of the Great Weigh House samples. However, the degree of contamination is much more uniform in Trench A. Maybe the Great Weigh House rooms were used for different purposes, hence such vast differences — even in the range of 1500. Also, there is a high concentration of Ni (about 400 mg/kg) — signifi-cantly different from concentrations typically found in the historical layers of Krakow.

This value was confirmed in the metal analysis of the artefacts (see Fig. 5e–f). In sample W3, X-ray microanal-ysis confirmed that although there is a pure copper matrix (99.84 ± 0.07%), locally there is also an intermetallic phase consisting of iron, copper, magnesium and nickel. Based on X-ray fluorescence spectroscopy, it was shown that in the sample examined, the highest concentrations are of arsenic (26.11 ± 0.03%) and copper (25.27 ± 0.02%), with a significant concentration of nick-el (17.87 ± 0.01%), iron (15.55 ± 0.01%) and antimony (7.00 ± 0.09%).

It was interesting to trace lead accumulation changes within buildings serving as warehouses for the Great Weigh House. These buildings were located at trench A, at the Bracka Street exit (see Fig. 2). Due to the fact that the lead slab was discovered there, earth (sediment) samples were taken from the top and bottom levels of layer 118, adjacent (from the outside) to the wall of an unidentified room or building, in a place susceptible to leachate accumulation (Fig. 5c). Also, the layer profile labelled AR-2W was sampled, starting from its first layer up to the level of the modern fill (Fig. 5a). The above mentioned wall was intersected, at right angles, by a communication route with a pavement and gutter, where samples of waste sediments and earth were taken (see Figs. 2b–c, 5c). The chart shows, based on the example of lead and copper, the contamination level of the earth and sediments.

Within the profile (see Fig. 5a), up to the level of modern fills, contamination is present even in the sandy substratum at an average level of 500 mgPb/kg; in the case of copper, the level of 120 mg/kg also points to the storage of raw material (copper) here. Lead contamination is definitely higher — also within the cobbled area and the gutter. Maybe the raw materials (copper and lead) were stored (separately) in storage rooms in this area, to which they (mostly lead) were transported by road.

The Great Weigh samples from the investigated rooms were analysed from the perspective of their deposition level, and in this way a simplified timeline of (the variability of) contamination was obtained for the Main Market Square substratum in this area, as the historical layers were created. In this way, it was ascertained that from layer 207.90 to 208.30 m AMSL, copper content increases 200 times, and lead — as much as1000 times. This increase is especially noticeable in the level deter-mined at 208.30 m AMSL (Fig. 5b).

Analysis of concentration changes and their indis-criminate dating and matching with the history of this place and town is not, of course, recommended, because the deposit growth was uneven in particular rooms and resulted from the designation and specific usage of a given room. Also, the metal accumulation may have resulted from the same causes, but should not be translated into the same mechanism in a broader perspective. Nevertheless, the degree of contamination of the deposits, layers and re-deposits shows that the Great Scales were not only used for weighing the raw materials, but also that some metal melting took place there for a considerable period of time.

Earlier research showed that this contamination could have caused some hydro-chemical anomalies in the underground waters of the Main Market Square, which had been noted earlier by Kleczkowski (1967). It is difficult, however, to trace the migration paths of these metals, because at the solid ground level, directly beneath a very contaminated layer, there are only slightly increased values. In the Great Scales area, the values for Cu and Pb are respectively, 30 and 70 mg/kg (Pawlikowski et al., 2008). The recognised sewage systems mainly disposed of meteoric and sewage waters, rather than serving to protect from anthropogenic modification of the environ-ment. They also spread metals in an uncontrolled way in the Main Market Square environment and other lower areas situated within the water runoff from the medieval utility levels (pavements, abode flooring, floors), as well as along the town streets and other communication routes.

A special role was played here by gutters and waste water troughs — which enabled horizontal transportation of pollutants — and also other structures (e.g. walls) that cut through layers made from compact loam and organic formations, which facilitated the seeping of pollutants into the ground. Pollutant migration could take place both at the time the pollutants were created (generally speaking, when the metals were produced, worked with and traded), and in later centuries, when metal particles were deposited in the earth, and then processes of resorption and remobilisation took place slowly.

During the earth and construction works connected with alterations to the Great Weigh House, the contaminated earth could have been used for filling cellars and for levelling ground. That is how in modern fills, contamination can appear that is not caused by a continuation of the activity that actually generated it, but by the shifting of contaminated earth from some older layers.

So it follows that in research assessing metal concentrations in earth, aimed at evaluating the level of contamination of the old Krakow environment, samples should be taken exclusively from old and preserved utility levels, namely from abode flooring, cobbled areas and floors and the waste layers resting on them. The research conducted so far has yielded interesting results, confirming the very important role of copper in the development of medieval Krakow; this will broaden the scope of knowledge concerning the use of semi-finished metal, copper and bronze objects, as well as finished, cast artefacts in metal production and trade in Europe. Also, it is worth remembering that in the Main Market Square area, starting from a depth of 80–100 cm (see Fig. 5a), there are medieval strata present, formed in the 15th or even 14th centuries. Thus, everything that was present and recorded within these layers is connected with that period, including the heavy metal contamination determined there.

In the Middle Ages, (besides lead) copper and tin be-came the basis for making alloys in casting workshops. Written sources and also research results undoubtedly point to large scale metal production conducted in medieval Krakow. Finds of melted copper fragments and cop-per raw material in the form of a round slab in the vicinity of the Great Weigh House (see Fig. 1) show that there must also have been a melting shop — a non-ferrous metal works. The slab found here has an irregular shape, and — below a thick layer of earth and corrosion products — a fracture with a characteristic red-brown colour has appeared, which indicates that the metal was not only weighed but also divided here.

It is worth remembering that the Great Weigh House institution was connected with trade. Its activity was based on a special charter or privilege, granting the town a monopoly in this respect. Greater trade turnover in a given town was connected with the obligation to weigh the goods there. The weighing was connected with special fees, and often also additional levies, which benefited the town. Copper, similarly to lead and iron, was weighed on the Great Scales, which were hundredweight scales.

During the period when the Great Scales functioned, there was exceptional contamination of the layers formed around them. In the Great Weigh House, irregular, porous lumps of copper were found, resulting from the processing of this metal, which must have been carried out in this place. This is attested to by the fact that parts of furnaces were discovered in the actual Weigh House itself. The great number of small, green particles, which are shreds (and also larger fragments) of oxidised copper, distributed within a 30-cm earth layer — accompanied by occurrences of lead — constitute material proof of the weighing, heating, dividing and marking (and — what follows — distribution) of copper.

A slab of copper from the Great Scales (which are al-so known as the Lead Scales) in Krakow assumed the shape of a hollow in the earth in which it lay, and so it must have been created there, i.e. next to the Scales, maybe from scrap material resulting from pieces that were cut off from larger slabs, mixed with inclusions and shavings of lead and copper.

The lower (but still high) copper and lead concentrations in its immediate neighbourhood, especially in buildings in the area of Bracka Street, probably testify to their auxiliary function: the warehousing of raw materials. The finds of coloured metal lumps — especially a lead slab weighing 693 kg, which is a unique find because of its size — come from this area. Other areas of the Main Market Square were probably polluted by the spreading of contamination on shoes or by means of transportation used at that time.

Studies of the effects of metallurgical processes in the area of the Great Weigh buildings on the Market Square in Krakow have shown that metal artefacts and geoartefacts in the form of contaminated earth and water sediments constitute good material for in-terdisciplinary analysis.

The present paper has attempted to demonstrate that metal artefacts and the chemical composition of the archaeological layers in which they were deposited can fulfil the role of geoindicators. Interdisciplinary studies by archaeologists, metal scientists and geochemists enable the full characterization of layers, including determining their origin, and even sometimes chronology. The state of preservation of artefacts in the ground — when analysed in comparison with the ground’s physicochemical properties — also serves as an indicator of the best methods of preservation of archaeological sites.

In the light of the latest archaeological researches on the Main Market Square in Krakow, the role of this city in the copper trade has become more evident (Buśko et al., 2009; Garbacz-Klempka and Rzadkosz, 2009; Schejbal-Dereń and Garbacz-Klempka, 2010). Copper came to Krakow mainly from Koszyce. Round or oval ingots, formed in Hungarian smelters, were weighed and divided on the Market Square in Krakow, from where they were sent on. Krakow gained the privilege of a right to store copper in 1306, which enabled it to mediate in the Hungarian copper trade, which ran through Gdańsk to Flanders and England (Kutrzeba, 1902; Wyrozumski, 1992, 2007). Krakow’s significance was confirmed by its membership in the Hanseatic League, the most powerful trade organization of the Middle Ages (Kutrzeba, 1902; Wyrozumski, 2010). Among Hanseatic towns, Krakow was known as Kupferhaus, which means Copper House (Rzadkosz et al., 2012; Wyrozumski, 1992; Wyrozumski, 2007).