The results of a study of the composition and structure of 29 fifteenth-seventeenth century archaeological objects (various sized pieces of slag as well as several metal and ceramic finds) are presented in the work. The finds were discovered in 2002 in Vilnius under Gedimino Avenue and Dysnos Street (in the then suburb of Puškarnė) while making archaeological excavations during the reconstruction of Gedimino Avenue.

The work describes in detail the exterior and macrostructure of all the finds and establishes that the slag finds differ in form, size, and heterogeneity from the Lithuanian smelting slag studied up until now.

A diagram of the composition of iron smelting and smithing slag from various countries as well as the slag found under Gedimino Avenue and Dysnos Street and a comparison of them are presented in the work. It was established that in the studied slag, especially in that found under Gedimino Avenue, there was significantly less MnO and P2O5 and more SiO2 than in the previously studied smelting slag found at other locations in Lithuania. Furthermore, it was noted that the composition of the slag finds from Gedimino Avenue and Dysnos Street is different. It perhaps shows that the composition of iron ores, from which were made the blooms, was probably different too. The work also presents and analyses the results of the chemical composition analysis of the metal objects.

Through phase composition and microstructure tests on samples, it was established that the slag was especially heterogeneous. Not only was typical fayalite slag detected in it but also various quantities of charcoal, metal iron, iron corrosion products, magnetite, large wustite inclusions, quartz crystals, and glass. Many photographs illustrating the microstructure are presented in the work and the possibilities for the formation of these phases are discussed. Besides this, the structure of the metal and ceramic objects is also examined. In summarising all the research results, it is confirmed that smithies operated in Vilnius during the fifteenth-seventeenth centuries near the places where the slag was found. At both Gedimino Avenue and Dysnos Street, the slag that was found could have been formed by heating various iron objects in a forge. The forge-processed metal iron finds and pieces of copper alloys could have been the refuse of forge work. Ceramic shards could have probably been parts of a smithy’s equipment.

The work discusses the course of and conditions for the creation of smithing slag, presents drawings of the possible forms of the smithing hearth bottom, and briefly discusses the activities, which could have taken place in the smithies.