An iron stamp is a mark that is wrapped in an iron piece before it leaves the forge or mill where it was made. Between the 1600s and the 1800s, almost all iron was made in the form of bars. It was a requirement that all bars be stamped and the iron stamp developed into a brand for each iron mill.
The marking of iron with the manufacturer’s stamp has very old ducks. Already in the 1400s the quality of the Swedish iron was checked, but it was during Gustav Vasa in the 1500s that stamping iron began to gain its great importance. New methods for iron making had come to Sweden, and the iron began to be produced in long bars instead of the moon-shaped lumps or “osmunder” that had previously existed. Bars are made by heating and bursting pig iron: Remains of carbon and slag that are present in the pig iron are pressed under heavy water-driven hammers, and bars of malleable iron with consistent quality are formed. The iron became one of Sweden’s most important export goods, and through quality control it sought to protect the international reputation of the Swedish iron and maximise export income. Stamping the rod iron became the key to the control system, and the controls were carried out by special “waggers.” A substandard rod iron was thrown to the side, and it was possible to identify the forge or iron mill where it was produced. Through his interest in the history of the Swedish Iron Management, the engineer Bo Molander began collecting on bar iron stamps. Initially, during the 1950s, he examined the remains of the hammers and forges where the bar iron had been produced. The finds were meager, and Bo Molander came to focus his search instead on the places where the bar iron had been used - such as drawbars, anchor ends and screed bars in old buildings. In the early years of the 1960s, what came to be called the “demolition rage” in Stockholm city centre and Bo Molander realized that the house remains - which could be over 200 years old - were a unique source of old bar iron, and hopefully rod iron stamps. The Samland was very successful and Bo Molander was granted permission to search the demolition masses during the construction sites' work free weekends. At the same time, he took advantage of all Stockholm’s house drawing and plan archives to date the house, floor plan or expansion in which he found the stamped iron. Until about 1980, Bo Molander had collected almost 1300 Swedish bar iron stamps. Through his research it was possible to specify a time span for each individual stamp, thus creating not only a unique picture of the Swedish iron mill’s production history, but also an invaluable tool for dating old houses and buildings. Documents and Bo Molander’s documentation and documentation about the barb iron stamps find sites can be found in the Technical Museum archives.