## 1 Introduction  
In the industrial context, traceability refers to the ability to obtain information on the history, location, and use of goods produced along the supply chain, from the origin of raw materials to the final delivery of products to consumers. Traceability is key to ensuring the transparency of the production process, as it guarantees that each production, processing, and distribution step or phase is recorded, facilitating subsequent verification. In short, traceability allows manufacturers to clearly trace the path of raw materials and the various stages of production, and thus to detect problems or errors along the process, which in turn allows them to be effectively solved [1]. Traceability is also key to complying with applicable regulations in sectors such as pharmaceuticals, food, or manufacturing, where controlling the quality and safety of products is of paramount importance. Traceability also serves as an instrument to improve the societal perception of companies and increase customer confidence, as it conveys a commitment to transparency and compliance with society, allowing customers to obtain information at all times on the origin and the different processes that goods undergo before being acquired. The concept of traceability is necessarily complex and multifaceted due to its various purposes and objectives [2]. A first basic definition of traceability would be the ability to access all or part of the information relating to something, throughout its life cycle, by means of recorded identifications [3]. According to the ISO 9001 quality standard [4], traceability is the ability to trace the history, application or location of something. This standard further specifies that traceability can refer to the origin of materials and parts, the processing history, and the distribution and location of a given product after delivery. Blockchain technology became a reference technology to support traceability solutions because it provides a transparent, auditable and immutable record of events and transactions [5]. Transactions within a blockchain are stored in blocks, each cryptographically linked to the previous one, making it virtually impossible to alter the information once recorded on the blockchain, but remaining easily verifiable at the same time. On the other hand, blockchains operate as decentralised systems, with no central actors but a network of nodes or devices that share copies of the chain of blocks. All processes are executed by the nodes that make up the peer-to-peer network in which blocks of information are shared and consensus mechanisms are implemented to guarantee that all peers in the network agree upon the content of the blockchain (i.e., which new blocks are deemed valid to join the chain), thus guaranteeing auditability without the intervention of a centralised controlling body [6]. If all relevant events in the life journey of an asset are stored in a blockchain, its evolution from its origin to its destination can be traced at any time with the information stored in the blocks of that blockchain (i.e., asset identification, location, ownership, properties, etc.). Events can be captured by means of the usual tools in traceability systems (e.g., IoT devices, RFID tags, GPS locators, etc.). Once the data are available on the blockchain, anyone with access to it, the general public in the case of a non-permissioned blockchain, can access any previous record, which in turn cannot be modified or deleted [7]. In short, blockchains improve transparency, traceability, and auditability in supply chains, and we can find a multitude of proposals in a wide range of fields, such as agriculture and food [8; 9; 10], pharmaceuticals [11; 12; 13], automotive [14; 15], textiles [16; 17], timber [18; 19], luxury goods [20; 21], or manufacturing [22; 23], to name a few relevant examples.