Glassworking – transformations in the organization of craft and glass production technology in Poland in the 13th–14th/15th century

Abstract

In the history of glassworking the 13th century was a significant period because during it changes occurred that initiated a new stage in its development. These changes were noticeable both in the organization of glass craft, glass foundry technology and product range. However, this period is the least known in archaeological terms, hence the main source of information about workshops operating in the 13th and 14th centuries, and even much later, i.e. until the end of the 15th century, are records in documents listing the glass foundries or glass workers as well as names of localities that indicate their glass working function. The knowledge of glass technology used in Poland in these centuries is mainly based on some results of physico-chemical examination of finds and is insufficient. The aforementioned transformations began in the second half of the 13th century. Prior to this period characteristic features for the early medieval glass working endured. Their features were a diversity of organisation in production methods, a diverse range of products as well as a multitude of impulses influencing this type of production in Poland. Glass workshops produced jewellery, stained glass, vessels, and floor tiles and were also involved in the glazing of pottery. At these workshops the following types of glass were found: lead-silicate, potassium-lead-silicate, sodium-lead-silicate or lead- silicate with glass cullet. Questions concerning the relationships and differences between the early medieval and late medieval glass working are to-date unexplained as are issues related to the reasons for organizational changes that occurred in the latter period; one of the most important was the location of foundries. In the Early Middle Ages they were situated only in the major centres of economic and political life of the country; they were established during a period of the advanced development of other crafts and international trade – between the 10th and the first half of the 12th century. In contrast, in the second half of the 13th century, glass production workshops were located outside areas of dense settlement, in forests, which was where their raw material and fuel bases were located. Initially forest foundries operated briefly and had a fairly impermanent structure. They were abandoned after the felling of the forest in the immediate area and glass workers moved to a new, often nearby place. However, some foundries operated in the same place for a few decades or even longer. In these workshops glass was comprised of mainly basic raw materials. The results of glass chemical composition analyses indicate that in the late Middle Ages in Poland the lime-potassium-silicate formula was commonly used. Until the 14th century lead glass was still produced. During the period in question available basic raw materials such as sand, wood ash or potash, lead, and various lime raw materials were used. As in the previous period such complementary technological practices as glass discolouration and staining and possibly making it opaque were employed. In a similar manner raw materials were also cleaned and dried. Unfortunately, we do not know anything about the appearance and construction of glass furnaces at that time. The only remains of such features were discovered in Cicha Dolina dating from the third quarter of the 13th–first half of the 14th century and have not been studied in detail to-date. The remains of a glass furnace found in Italy dated to the turn of the 14th century as well as iconographical sources from the first half of the 15th century indicate that two- and three-level furnaces were used and that they served all three functions (a working furnace for glass founding, a furnace for forming products and a cooling furnace). In the period in question in Poland the number of vessels and the glazing of vessels increased significantly and the range of these products widened. In the 13th century in the history of glassworking in Poland transformations began that led to more intensive development in this field of production, and thereby increasing the role that the production of glass began to play in everyday life of society.