Brass - History - Brass Making in Renaissance and Post Medieval Europe

Brass Making in Renaissance and Post Medieval Europe

The Renaissance saw important changes to both the theory and practice of brassmaking in Europe. By the 15th century there is evidence for the renewed use of lidded cementation crucibles at Zwickau in Germany. These large crucibles were capable of producing c.20 kg of brass. There are traces of slag and pieces of metal on the interior. Their irregular composition suggesting that this was a lower temperature not entirely liquid process. The crucible lids had small holes which were blocked with clay plugs near the end of the process presumably to maximise zinc absorption in the final stages. Triangular crucibles were then used to melt the brass for casting.

16th century technical writers such as Biringuccio, Ercker and Agricola described a variety of cementation brass making techniques and came closer to understanding the true nature of the process noting that copper became heavier as it changed to brass and that it became more golden as additional calamine was added. Zinc metal was also becoming more commonplace By 1513 metallic zinc ingots from India and China were arriving in London and pellets of zinc condensed in furnace flues at the Rammelsberg in Germany were exploited for cementation brass making from around 1550.

Eventually it was discovered that metallic zinc could be alloyed with copper to make brass; a process known as speltering and by 1657 the German chemist Johann Glauber had recognised that calamine was "nothing else but unmeltable zinc" and that zinc was a "half ripe metal." However some earlier high zinc, low iron brasses such as the 1530 Wightman brass memorial plaque from England may have been made by alloying copper with zinc and include traces of cadmium similar those found in some zinc ingots from China.

However the cementation process was not abandoned and as late as the early 19th century there are descriptions of solid state cementation in a domed furnace at around 900–950 °C and lasting up to 10 hours. The European brass industry continued to flourish into the post medieval period buoyed by innovations such as the 16th century introduction of water powered hammers for the production of battery wares. By 1559 the Germany city of Aachen alone was capable of producing 300,000 cwt of brass per year. After several false starts during the 16th and 17th centuries the brass industry was also established in England taking advantage of abundant supplies of cheap copper smelted in the new coal fired reverberatory furnace. In 1723 Bristol brass maker Nehemiah Champion patented the use of granulated copper, produced by pouring molten metal into cold water. This increased the surface area of the copper helping it react and zinc contents of up to 33% wt were reported using this new technique.

In 1738 Nehemiah's son William Champion patented a technique for the first industrial scale distillation of metallic zinc known as distillation per descencum or "the English process." This local zinc was used in speltering and allowed greater control over the zinc content of brass and the production of high zinc copper alloys which would have been difficult or impossible to produce using cementation, for use in expensive objects such as scientific instruments, clocks, brass buttons and costume jewellery. However Champion continued to use the cheaper calamine cementation method to produce lower zinc brass and the archaeological remains of bee-hive shaped cementation furnaces have been identified at his works at Warmley. By the mid-to-late 18th century developments in cheaper zinc distillation such as John-Jaques Dony's horizontal furnaces in Belgium and the reduction of tariffs on zinc as well as demand for corrosion resistant high zinc alloys increased the popularity of speltering and as a result cementation was largely abandoned by the mid-19th century.