(2020) 12:141 Archaeological and Anthropological Sciences https://doi.org/10.1007/s12520-020-01115-0 ORIGINAL PAPER Influence of conservation of copper and bronze artefacts on traces of production and use-wear Dawid Sych 1 & Kamil Nowak 2 & Marcin Maciejewski 3 & Beata Miazga 2 & Justyna Baron 2 Received: 14 March 2020 / Accepted: 8 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Although studies of production traces and use-wear in copper and bronze artefacts have been conducted already for a few decades, the influence of the conservation on these items did not receive much scholarly attention. It seems quite surprising, as traceological analyses focus most often on conserved artefacts from museum collections. In the following article, the authors examine the impact the conservation has on traces of production and use-wear in bronze artefacts coming from three Bronze Age hoards: Karmin IV, Paszowice and Lubnowy Wielkie. All deposits have been analysed both before and after the conservation. Our results show that traces of production and use-wear might either become highlighted or fade in the conservation process. Thus, we should be extremely cautious when examining copper and bronze artefacts for the presence of these traces. The problem is especially critical for items which were not examined directly after the discovery but come from the already conserved museum collections. Keywords BronzeAge . Metal hoards . Metalwork wear analysis . Use-wear . Traceology . Productiontechnology . Conservation Introduction Traces of production and use-wear on artefacts made of copper and bronze have been studied for over 30 years now (Dolfini and Crellin 2016: 79–81). However, it was only the last decade, which saw a significant increase in interest in this subject. Many questions remain unanswered, and the method itself is still struggling to become a well-established scientific field of research. In this article, we also refer to metalwork wear analysis as ‘traceological analysis’ and ‘use-wear analysis’. The former term is slightly broader and includes both studies of use-wear and technology. The latter is more narrow and focuses only on the traces of use. Metalwork wear analysis aims to record traces on the surface of metal artefacts, compare them to the existing * Dawid Sych 1 Stowarzyszenie Naukowe Archeologów Polskich Oddział Górnośląski, Bytom, Poland 2 Institute of Archaeology, University of Wrocław, Wrocław, Poland 3 Institute of Archaeology, Maria Curie-Sklodowska University, Lublin, Poland experimental data and interpret as caused by use or other events and actions, such as the post-depositional processes and conservation. Traceological analysis often combines both studies of use-wear and technological traces. Establishing their relation to each other might provide further insight into the artefact interpretation (Gener 2011; Kuijpers 2015). The surface of a metal artefact reflects the sum of actions performed on the object between its production and deposition, as well as in the course of the post-depositional processes and conservation. What we see today might not show what exactly happened to the object in the past. The use-wear might have been removed through repairs already before the deposition and destroyed by the post-depositional processes or under conservation (Horn and Holstein 2017). Most of the traceologists work on artefacts from museum collections, often many years after the discovery and conservation of the finds (i.e. Coloquhoun 2011; Horn 2013; Roberts and Ottaway 2003). Therefore, the crucial research questions are that of the influence of the post-depositional processes and conservation on the preservation of the existing and the emergence of new traces. The discovery of hoard IV from Karmin in 2017 encouraged the authors to reflect on and answer these questions. The hoard consisted of copper and bronze tools, weapons, dress accessories and other miscellaneous items. All of them 141 Page 2 of 12 were subject to microscopic analyses both before and after the conservation. A thorough examination demonstrated that in some of the cases, the traces observed on the objects which went through the conservation process differed from those observed before the conservation. These results made the authors take a closer look at the deposition conditions and conservation techniques. Meanwhile, similar analyses were developed for two other hoards—discovered in 2015 in Paszowice and in 2017 in Lubnowy Wielkie. The results were entered into the database created for the Karmin IV hoard (Fig. 1). Three hoards In 2017, a hoard consisting of 40 metal artefacts of a total weight of 5037.95 g and two ceramic objects was found near Karmin (Fig. 2) in SW Poland and handed over to the Provincial Office of Heritage Protection (Wojewódzki Urząd Ochrony Zabytków). The discovery was all the more thrilling that the same area yielded three more hoards discovered in the late nineteenth and early twentieth century. All of the Karmin deposits were subject of a recently published, 2-year research project (Baron et al. 2019). Fig. 1 Location of the three hoards: 1, Karmin, dist. Milicz; 2, Paszowice, dist. Jawor; 3, Lubnowy Wielkie, dist. Ilawa (D. Sych) Archaeol Anthropol Sci (2020) 12:141 The amateur finder informed that he had seen some isolated metal items scattered on the ground where the ceramic vessel was hidden. Below the vessel, more artefacts were identified. The deposit included sickles (2), socketed axes (16), knives (3), a chisel, a punch, a needle, daggers (2), spearheads (3), a pin, circular dress accessories (8), lumps of raw material (2), a ceramic vessel and a bottom fragment of a ceramic vessel. As in the other hoards, the artefacts originated in the Montelius phase V of the Bronze Age (ca. 950–750 BC). In September 2015, on the surface of a freshly ploughed field, the hoard from Paszowice (Fig. 3) came to light. The spot was situated ca. 900 m north of a small stream in the area featured mainly with podzolic and pseudo-podzolic soils. Since the discovery was accidental and did not occur during regular archaeological excavations, we are not able to precisely determine the deposition context. The amateur finder realised that the excavated objects could be of antique origin and brought them to the Regional Museum in Jawor. Judging from the objects’ soiled surfaces, they arrived in the museum shortly after the discovery. Their general condition was satisfactory, and most of their surfaces featured an intensely green patina. The hoard consisted of 34 metal items: dress accessories, tools, weapons, fragmented objects and shapeless lumps of Archaeol Anthropol Sci (2020) 12:141 Page 3 of 12 141 Fig. 2 Hoard no. IV from Karmin (T. Gąsior) raw material, as well as half of a casting cake. Dress accessories included eight annular rings with circular, quadrangular and U-shaped cross-sections. The discovered weapon was an almond-shaped spearhead, while the tools were axes and Ushaped or strongly arched tanged sickles. Two of the sickles were complete and two found in fragments (the handle and the tip were separated). The inventory also included a fragment of a handle covered with cut marks and a fragment of a central part of the blade. The deposit also contained four socketed axes in various states of preservation, all of which belonged to different subtypes of the Central Danube type (Kuśnierz 1998: 11–12, 15, 22). Some of the objects survived only in fragments. Those include a flat plate, an object with a slender socket and a loop, a casting jet, an oblong ingot widened towards the end, a sprue cut-off from a socketed axe, two fragments of bent wire and two fragments of bent plates of various thickness. Tanged sickles have their backs reinforced with a single rib. Such sickle forms are mainly associated with hoards dated to BA V. The chronology of the axes from the deposit spans from BA III to the first half of BA V. Specimens with rich decoration or covered with a pseudo-wing ornament (on the upper part of the socket) are part of a set dated to final BA IV. Bronze rings typically occur with BA IV and BA V materials. Spearheads are the least chronologically sensitive artefact category here and might be found with objects dated both as early as to BA III and as late as to BA V. Considering all that, it seems justified to date the deposit to final BA IV or the beginning of BA V (ca. 950–750 BC). A complete typo-chronological analysis is to be published shortly (Nowak and Sielicka in press). In 2017, a member of Towarzystwo Miłośników Ziemi Suskiej (a group of local history enthusiasts) discovered a hoard in Lubnowy Wielkie (Fig. 4) while conducting a metal detector survey. They brought the metal objects, the report specifying the location of the site and the catalogue of artefacts 141 Page 4 of 12 Archaeol Anthropol Sci (2020) 12:141 Fig. 3 Hoard from Paszowice (A. Muła and K. Nowak) to the Provincial Office of Heritage Protection, Branch in Elbląg, which later transferred them to the Ostróda Museum. A comprehensive publication of the Lubnowy Wielkie hoard—including archaeological and archaeometallurgical analyses—is currently under preparation (Maciejewski et al. in press). The hoard was discovered within an elevation rising above a mild terrain depression which until the eighteenth century was a lake. The excavations (2 × 2 m trench) conducted in the place of deposition did not detect any additional structures or metal artefacts which might have belonged to the hoard. The early Iron Age and Bronze Age pottery sherds recorded during the excavations (Lusatian Urnfield culture) did not come from one vessel—as differences in colour suggest. The location of the hoard and the presence of sherds might indicate that the prehistoric inhabitants frequented the site around the deposition time (broadly understood as 600–800 years; Szczepański 2017). The hoard consisted of five objects made of copper alloys which all served as dress accessories. The assemblage included a neck collar (sloped, longitudinally ribbed, Fogel J. 1988: 59–61, or Quedlinburg type, Nørgaard H.W. 2011: 73–74), a cuff bracelet, two ribbon-shaped, so-called pseudospiral bracelets (both II phase/Wielkawieś phase; Fogel J. 1988: 24) and a double spiral pendant suspended on one of the pseudospiral bracelets. The items were stylistically homogeneous and displayed features characteristic of the CircumBaltic zone in the late Bronze Age. The hoard resembles one or two sets of jewellery. It originates in Montelius phase V of the Bronze Age, which we might synchronise with ca. 950– 750 BC. Methods Conservation of the artefacts Due to the natural oxidation process, almost all of the metal artefacts need conservation. The thickness and composition of the corrosion layers formed through this process depend on the natural properties of each metal and the deposition environment. While copper oxidises slowly, its alloys (more prevalent in the material culture) corrode faster due to the presence of highly active metals, such as tin or zinc. Those have much more negative electrochemical potential than copper. Therefore, the conservation procedures for copper alloys must both accommodate the characteristics of copper and other alloy additions. In some bronzes, tin causes the formation of cassiterite (SnO2) in the outer corrosion layers, which protects the metal core underneath. In brasses, zinc disappears from the alloy in the course of the dezincification process (Scott 2002: 11). Hence, the corrosion of copper alloys is generally dependent on the chemical properties of alloy additions, i.e. zinc, tin, arsenic and antimony. The formation of the corrosion layers is also determined by the post-depositional factors, such as the time the item spent in a particular environment, the type of soil, the presence of specific moulds, bacteria, pH, the concentration of chloride ions and other parameters (Oudbashi 2015). The artefacts undergo conservation treatment both due to their state of preservation (often miserable) and for aesthetic reasons. In the past, many electrochemical and chemical conservation methods involved the complete removal of corrosion products. However, treatments which might destroy the Archaeol Anthropol Sci (2020) 12:141 Page 5 of 12 141 Fig. 4 Hoard from Lubnowy Wielkie (N. Lenkow) finds or the surface patina are no longer acceptable in the conservation of archaeological finds. The original patina is composed of secondary corrosion products, such as malachite and azurite. It shall be left intact, as it testifies the historical contexts of the item and is of great aesthetic value. Therefore, the practice of treating copper-alloy artefacts with sodium hydroxide is largely out of use (Scott 2002: 98; Megahed 2014). Immersing the object in 10% sodium hydroxide with zinc granules reduces the corrosion products (including all of the patina), as well as causes zinc from the solution to form deposits on the surface (galvanisation). Instead, Rodgers (2004: 114) recommends electrolytic reduction using sodium carbonate or sodium bicarbonate (0.25–0.5%) as an excellent method to extract chlorides and remove corrosion—with a current density below 2 Amps. Removing the corrosion products with sodium sesquicarbonate solution (10% water solution) might also prove problematic. The main challenges here are to the secondary deposition of metallic copper (Scott 2002: 254) and the formation of a new blue-green malachite layer on the surface (Hamilton 1999: 76). Other chemical methods used with copper alloys include the use of sodium polyphosphate, acetonitrile, citric acid and alkaline sodium dithionite—as mentioned by Scott (2002: 355–373). Some of these treatments are very aggressive for the archaeological copper-based items. On the contrary, a 5% water solution of sodium carbonate used for artefacts with bronze disease (Hamilton 1999: 76–77, Scott 2002: 98, 367; Cronyn 1990: 229) causes significant chloride extraction and is very gentle for the patina. The only one possible side effect is the possible formation of black tenorite. 141 Page 6 of 12 Mechanical cleaning usually follows the chemical and electrochemical procedures. The tools and substances used in this process include, e. g. glass fibre brushes, painting brushes, dental picks, water and crushed walnut shells and glass. Glass fibre brushes and crushed glass might scratch the surface, while painting brushes are too gentle to clean most of the finds effectively. Therefore, many conservators use various types of electrically operated metal brushes (Robbiola et al. 1993; Cronyn 1990: 64–65; Turner-Walker 2008: 68), as well as jeweller’s tools. The latter come in different shapes and sizes with bristles of metal, natural or synthetic polymers. While using brushes, it is essential to remember that the tool must always be softer than the cleaned material. Furthermore, we must avoid situations in which pieces of the abraded tool adhere to th e clea ned material (Domasłowski 2011: 515; Cronyn 1990: 64–65), which might happen while cleaning bronzes with brass brushes. Thus, this treatment requires exceptional care. After the cleaning, the artefacts require stabilisation. For artefacts without chloride ions, storage in proper conditions is sufficient: RH must be lower than 45% and air contamination (dust, chlorides) eliminated. Many artefacts are stabilised with the use of inhibitors, especially benzotriazole (BTA) dilute solutions (Cronyn 1990: 228–229; Scott 2002: 276–381; Nosek 2008: 40–41). Other ways of protecting the artefacts include applying polymer coatings, mainly of synthetic resins like Incralac (with BTA in composition), Ormocer or Paraloid B72. Proper storage is the last step in the stabilisation of archaeological artefacts. Ideally, the relative humidity in the controlled storage conditions shall be below 45%, as the items might still contain some amount of chlorides. Cuprous Fig. 5 Karmin, hoard no. IV. Negative results of conservation on artefacts. Traces of production on the hilt of the dagger (top) and use-wear on the knife (bottom) have disappeared. Photographs taken with Conrad microscope (D. Sych and K. Nowak) Archaeol Anthropol Sci (2020) 12:141 chloride with air oxygen and moisture might turn into cupric chloride and basic cupric chloride. The former may, in turn, react with copper and convert it into a copper compound (Goffer 2007). RH below 45% is possible to obtain by immersing the artefact in a polymer box with an adequate amount of silica gel (Scott 2002: 391). Artefacts found in Karmin, Paszowice and Lubnowy Wielkie were in a relatively good state of preservation, as the metal under the corrosion layers and soil residues was in a satisfying condition. In some places, bronze disease visible as light green and powdery excrescences or eruptions occurred. The presence of these structures required a ‘chloride action’—the object needed specific treatment to convert or seal the cuprous chloride (Hamilton 1999). In our case, we decided to remove the chlorides. First, they were taken off mechanically with diamond rotary burrs used by jewellers for grinding, engraving and polishing. The tools come in various sizes and shapes, which help penetrate even hardly accessible areas. After that, we continued the chloride extraction by treating the artefacts with sodium carbonate. Immersions in 5% aqueous Na2CO3 solution lasted for 8 weeks. After this step, the chemicals were neutralised with hot distilled water (Crittenden et al. 2012: Appendix C), and the surfaces cleaned with soft brass and polymer brushes. As soon as all of the corrosion products had been removed, we applied the final treatment. The surface was stabilised by immersing the artefact in a dilute solution of BTA (1% aqueous) for at least 24 h (Hamilton 1999: 77). After the sealing, the object was dried with hot air and covered with Paraloid B72 (5% solution in acetone, Welsh 2002: 243). Archaeol Anthropol Sci (2020) 12:141 Page 7 of 12 141 Fig. 6 Karmin, hoard no. IV. Positive results of conservation on the axe blade (top) and the spearhead (bottom). Use-wear on the axe and spearhead has become much more visible. Photographs taken with Conrad microscope (D. Sych and K. Nowak) Traceological analysis The study utilises traceological analyses of artefacts from all of the three hoards mentioned above. The cutting edges of the tools and weapons displayed both production traces and usewear. Such cases are already extensively discussed in the literature. As far as dress accessories and other miscellaneous finds are concerned, such examination is much harder since they have no ‘cutting edges’ vulnerable to damage. Lack of Fig. 7 Paszowice hoard. Negative results of conservation. Traces of surface preparation on the axe blade disappeared. Photographs taken with Dino-Lite microscope (K. Nowak) experiments and literature about the use-wear patterns on such items makes it impossible to make any credible conclusions. Nevertheless, comparative analysis of the traces of production and use-wear on copper and bronze artefacts is still relatively new in archaeology. Therefore, new studies are crucial for the further development of the method. Traces of production and use-wear have been captured with the use of (1) a Conrad portable digital microscope equipped with a 10 Mpx camera with × 10 to × 200 magnification as 141 Page 8 of 12 Archaeol Anthropol Sci (2020) 12:141 Fig. 8 Paszowice hoard. Positive results of conservation. Traces of hammering on the sickle blade became more visible after conservation. Photographs taken with macro lens (K. Nowak) well as (2) a Dino-Lite portable digital microscope with a 1.3 Mpx camera with × 20 to × 220 magnification. The photos were taken at × 20 to × 50 magnification. In our opinion, it allows for optimal visibility of the traces on the surface. As the authors conducted their pre-conservation studies independently, they did not use the same equipment. Ideally, the photographs should be taken both before and after the conservation using the same microscope and with similar lighting conditions, orientation and angles. Unfortunately, it is not always possible to meet these guidelines—both for technical and formal reasons. Moreover, maintaining a similar orientation and angle of the photographs, even though it sounds reasonable in theory, might not deliver a satisfying outcome. Different lighting conditions and cleaned surfaces of the artefacts might result in reduced visibility or lack of visibility under fixed angles and orientation. Therefore, we adjusted the photographs in such a way that they present the results of the analyses most accurately. After these analyses, the authors entered the results into a shared database. Full results of the microscopic analyses of the production and use-wear traces as well as other relevant information—for example, results of the analysis of the chemical composition of alloys—have been already published (Karmin; Baron et al. 2019) or will be published soon. Karmin IV Our examination showed that all of the tools and weapons from Karmin IV hoard had traces of use. The overall stage of wear of the socketed axes’ was low. Knives, sickles, spearheads and daggers displayed more intense use-wear or even were severely damaged. We did not identify any traces of use on dress accessories and other ornamental items. It does not mean that they had not been used, but as we have already mentioned, interpreting the use-wear on these categories of items presents significant difficulties. While the conservation of the artefacts from the Karmin IV hoard helped reveal some hidden traces of production and usewear, it made some other traces disappear. The latter situation happened twice, with a dagger (Fig. 5, top) and a knife (Fig. 5, bottom). Scratches covering their surfaces vanished with the layers removed in the conservation process. One axe and one knife from the hoard have traces of production in the form of casting errors uncovered through conservation. In eight of the cases, cleaning and conservation revealed hidden use-wear. In five items, the use-wear had a form of scratches, such as the well-visible, densely distributed lines on the axe’s blade (Fig. 6, top) and fine, delicate scratches on the edge of the spearhead’s blade (Fig. 6, bottom). In the further two cases, Fig. 9 Lubnowy Wielkie hoard. Negative results of conservation. The slight scratches (perhaps related to use-wear or post-depositional processes) visible on the pseuospiral bracelet no. 1 have faded after conservation (M. Maciejewski) Archaeol Anthropol Sci (2020) 12:141 Page 9 of 12 141 Fig. 10 Lubnowy Wielkie hoard. Negative results of conservation. Some of the scratches on the neck collar visible before conservation (deeper and grouped in a circle around the applied spiral ornament) ceased to be visible. Photographs taken with Dino-Lite microscope (M. Maciejewski) the newly exposed areas displayed blunting and, in one case, a crack/fracture. All of the traces indicate that the tools and weapons from the hoard were in use before the deposition. some other traces of production and use-wear, particularly traces of cold hammering on the sickle blades (Fig. 8). Lubnowy Wielkie Paszowice We performed the same research procedure on the tools from the Paszowice hoard. The traceological analysis utilised four socketed axes and two sickles. All of them bore traces of production, and two specimens displayed use-wear. The remaining artefacts lacked use-wear, which means that they had never been used or the traces were not macroscopically visible (compare Nowak et al. 2019). In the analysed case, the conservation procedure also had both positive and negative impact on the visibility of the traces. In axes, the well-visible traces of sharpening or grinding located parallelly to the blade’s edge (Fig. 7, images on the left) completely disappeared after the conservation (Fig. 7, images on the right). On the other hand, cleaning and conservation highlighted As we have argued above, traceological analysis proved to be the most productive research method for tools and weaponry. Their cutting edges reflect all of the actions performed on them throughout their ‘lifetime’. Of course, this record might be ‘wiped out’ by repairs or destroyed by corrosion, but even the general shape of the cutting edge might often suggest the usage pattern. The method might and shall also be applied to dress accessories, as we have done for the Lubnowy Wielkie hoard. The traceological analysis revealed details of the decoration and production techniques, i.e. casting errors. The results were especially conclusive for larger artefacts—the neck collar and the cuff bracelet (Figs. 9–10). In most instances, conservation exposed traces of production on the artefacts, but sometimes, it made them vanish from Fig. 11 Lubnowy Wielkie hoard. Positive results of conservation. Casting error (on the ribbon) became more visible on the neck collar, and scratches (probably related to surface polishing) after conservation have become more visible too. Photographs taken with Dino-Lite microscope (M. Maciejewski) 141 Page 10 of 12 the surfaces. It happened with one of the two pseudospiral bracelets and with the cuff bracelet, in which some of the scratches were no longer visible (Fig. 11). Discussion Microscopic analyses of the production and use-wear traces on metal objects, especially Bronze Age finds, have recently become increasingly popular in European archaeology. The more such analyses, the broader the database of the artefacts and the more we know of their biographies, meanings and events in which they were used (or rather in which they took part). Although traceological studies of other categories of finds provide an impressive amount of information, they also indicate that one must be aware of the processes taking place at different stages of item’s biography. The same applies to copper and bronze objects. Table 1 Archaeol Anthropol Sci (2020) 12:141 Traceological studies of the hoards from Karmin, Paszowice and Lubnowy Wielkie demonstrated that it is essential to conduct them both before and after the conservation of the artefacts. Even though in most of the cases, the conservation highlights the existing traces and helps reveal those unnoticed, it might as well erase them. Some traces of production and use-wear are only observable in the corrosion layers which are removed in the conservation process. Table 1 presents artefacts displaying most considerable differences in the preservation of traces before and after the conservation. It demonstrates that scratches connected to production (i.e. grinding and sharpening), use and repairs (i.e. sharpening) are most likely to disappear. Not only are they shallow but also the outer layer of the surface, in which they are preserved, is most vulnerable to damage. On the other hand, when properly conserved, scratches can become (more) visible. The same applies to minor casting errors, production traces (i.e. hammering) and damages (i.e. cracks). Selected artefacts from all three hoards showing the greatest discrepancies in the preservation of traces before and after conservation x, trace present; −, trace absent; entries in green, traces became visible or more visible after the conservation; entries in red, traces vanished after the conservation; pd, post-depositional Archaeol Anthropol Sci (2020) 12:141 We are aware of the fact that it is not possible to conduct a traceological analysis of every copper or bronze artefact before the conservation. In such situations, detailed documentation made before the conservation (including macrophotography) should be an alternative. In the age of digital photography and 3D photogrammetry, it no longer presents a technical problem. With this paper, we hope to convince the reader that sparing some extra time to preserve what might be irretrievably lost is worthwhile. The discussed examples demonstrate that the conservation of the artefacts is (along with repairs and corrosion) a factor which might severely affect the results of traceological investigations. If traces of production and use-wear might vanish from the surface of the artefact, lack of traces does not indicate that the item has never been used (Horn and Holstein 2017). Therefore, archaeologists studying traces of production and use-wear on copper and bronze items from museum collections should be particularly careful. Finds discovered in the nineteenth and the first half of the twentieth century, with often incomplete or lacking documentation, might be especially problematic. Conclusions Our paper is just a first step on the path to understanding the full scope of influence of conservation on copper and bronze artefacts. While we intend to broaden the spectrum of our research in the future, we hope that already this article will sensitise other scholars to the effects of conservation on the traces of production and use-wear. For example, it might be useful to examine the potential links between the traces before and after conservation and the chemical composition of the alloys. This procedure could provide some new data on the technical properties of the raw material (e.g. Baron et al. in press). However, this would require a much more extensive database. We would also like to encourage the archaeologists to work closer with conservators so that the results of traceological analyses become as accurate as possible. To this end, in the future, we hope to create a database consisting of traces on copper and bronze artefacts created by the tools used by the conservators. Acknowledgements We owe special thanks to M. Konczewska who participated in the conservation of the artefacts from Karmin hoard IV, K. Sielicka and A. Muła from the Regional Museum of Jawor as well as Ł. Szczepański from the Ostróda Museum for providing the artefacts from Paszowice and Lubnowy Wielkie hoards for the analyses. Last but not least, we would like to give our thanks to the reviewers who provided invaluable input and guidelines to ensure that the quality of this article meets highest standards. Funding information The project was financially supported by the Polish Ministry of Culture and National Heritage (no. 3469/18/FPK/NID) and the National Science Centre, Poland (project no. 2017/27/N/HS3/01097). Page 11 of 12 141 Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest. References Baron J, Maciejewski M, Jarysz R, Kuźbik R, Łaciak D, Łucejko JL, Mackiewicz M, Miazga B, Nowak K, Sych D (2019) Phenomenon of repetition. deposits from Karmin (Karmin. Fenomen powtarzalności). 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