brass: Museum Zinkhütter Hof

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Brass

Brass is an alloy (mixture) of the two metals copper and zinc, consisting of approximately 70% copper and around 30% zinc.

With respect to colour, brightness and lustre, brass (when freshly polished) bears a strong resemblance to gold. Not only for this reason our brass exhibition was given the subtitle "Stolberg's Gold". From the late 16th until the end of the 18th century, brass making was a "Golden Trade" which brought the manufacturers in the valley of Stolberg prosperity and wealth.

Nowadays, brass is made by melting together the two pure metals copper and zinc. Until the late 18th.century, however, pure metallic zinc was neither available nor even known. The alloy had thus to be made by utilizing calamine, a special zinc ore, mainly consisting of zinc carbonate or smithsonite.

: Cast brass plate between two "Bretanier"

In order to yield brass, crushed and pulverized calamine as well as pulverized charcoal together with pieces of copper were given into crucibles. At temperatures between 900 and nearly 1000 deg.C. the carbonate of the charcoal reacted with the oxygen of the ore, thus setting free the zinc as a vapour. These zinc vapours dissolved the still solid copper, thus forming the alloy.

Although the manufactured brass had a zinc content of only 30%, the required quantity of zinc ore was twice as high as the incorporated copper weight, because:

the zinc vapour was not completely absorbed by the copper fragments and
the zinc was added not as pure metal, but as an ore.

: Famous families

Consequently, brass making was almost exclusively restricted to areas with calamine deposits.

Quite strangely, the brass manufacturers were called "Kupfermeister" (copper masters). This may have been caused partly by the fact that they "imported" huge quantities of copper. However, there is still another reason for this peculiar nomenclature:

As already mentioned, the zinc content of the brass alloy initially emerged in a vaporized condition. When taking a crubicle out of the furnace and inspecting its content, the zinc could never be seen. The zinc vapour immediately escaped and reacted with the oxygen of the air to zinc-oxide. Indeed, pure metallic zinc was completely unknown at those times.

In consequence, copper as well as brass were both called copper. For a differentiation, the terms red copper for the pure metal and yellow copper for brass were commonly used. Likewise, the brass manufacturers were also called "Kupfermeister" and not brass masters as we would expect today.

: Drückbank

The migration of the protestant "Kupfermeister" from Aachen to Stolberg, which started around 1575, was supposedly caused by religious conflicts in the catholic Aachen. However, the natural resources in the valley of Stolberg were also important, if not decisive:

calamine deposits in the region of Breinig, Mausbach, Gressenich,
water power of the brook Vicht to drive mechanical hammers, bellows etc.
extending forests provided charcoal and
coal deposits to fuel the furnaces.

: Gear wheels

The buildings combining residences and factories of the "Kupfermeister" were (and are even today) called "Kupferhöfe" (copper yards), according to the idiomatic convention as mentioned above.

Initially (after 1575) the "Kupferhöfe" were built as fortified, defensible constructions. With increasing prosperity of the "Kupfermeister", the appearance of their residences changed quite drastically. In the first quarter of the 18th century representative mansions like Grünenthal and Rosental were erected.

: Bowls made of brass

At the end of the 18th century, conditions for the brass manufacturers worsened dramatically. The new technology of zinc smelting (zinc distillation) made the advantage of adjacently located calamine deposits obsolete. In the 19th century, brass making became of minor importance in Stolberg. Some of the "Kupfermeister" concentrated on manufacturing metallic semi-final products, others switched to the glass- and textile industry or invested in lead- respectively zinc smelting plants.