Page 64 - buvkeramika

64
Written sources of the northern Germany town Lüneburg contain evidence that a brick master was
subjected by oath to the town council. He was responsible for work organisation management of the
brick-kiln and for production quality, especially for preparation of the oven and ensuring of the brick
baking process as well as for management of other craftsmen’s work (Rümelin 1998, 38, 39).
Much more extensive information can be found about the operation of Livonian brick-kilns in the
Early Modern Times. In the late 17th century and 18th century documents of brick-kilns of Riga and
Jelgava/Mitau not only brick shapers and burners were mentioned but also auxiliary workers who dug
and brought sand and clay, provided water and wood, turned the bricks laid for drying, loaded the dried
production into the oven and after the baking process took it out (Zeida 1962, 126, 127). Bricks were
made and baked only during the warm season – starting from April or May till October or November.
In autumn and winter preparation works were performed bringing sand, preparing wood and selling the
baked bricks, taking them across the snow by sledge or along the waterways by boats (Zeida 1962, 130).
In autumn while the earth was not yet frozen clay was dug and heaped freely, two- or three-feet thick.
For one or several winters clay was left subject to wind, rain, frost, and sun so that noxious admixtures,
potassium nitrate and acids, would be discharged. After that clay became crumbly, well-disintegrating,
and easier for kneading (Schönauer 1815, 16–18).
When the mass was being prepared for brick making, gravel, sand and sometimes also lime was
admixed to well-pugged clay. Addition of sand was the most important, which attached water and thus
prevented cracking of bricks under the impression of changing weather conditions. Besides sand also
reduced shrinking of clay articles during the burning process. By admixture of gravel it was possible
better to regulate sintering of clay particles in high temperatures. Also the admixture of lime prevented
brick shrinking during the baking process. In some early 19th century regulations for Austrian brick
producers proportions of the recommendable components were provided with an indication that not
more than two or three parts of clean gritty sand could be admixed to one part of rich clay, and one part
of lime (Schönauer 1815, 22). Whereas in English literature it was noted that 30% admixture of sand was
the best proportion in clay mass for brick-making (Davey 1961, 64). Sometimes granulated straw was
admixed to the clay mass. During the burning process straw burnt down and thus the bricks became
more porous and provided better heat insulation (Zeida 1962, 137–139). Burnt straw or other organic
admixtures could create tiny particles of coal that can sometimes be seen on the surface or at the place
of fracture of medieval bricks.
In brick-kilns not only bricks but also roof tiles and floor tiles were made. Articles of building ceramics
were shaped by filling clay into oaken moulds. The moulds for ordinary masonry bricks were rectangular,
those for specially shaped bricks were correspondingly shaped, but for the Monk and Nun roof tiles the
moulds were trough-shaped. The mould was at first moistened and strewn with sand so that clay would
not stick to the edges. After that a lump of soft clay was taken and by force thrown into the mould, then
the maker pressed it into all the corners of the mould and with a special knife smoothed out the surface
of the emerging brick (Fig. 3).
As calculated by Ā. Zeida, in the late 17th century, a worker of a Riga brick-kiln made on average
60–130 bricks per day, but in Russia’s brick-kilns – 100–200 bricks (Zeida 1962, 140). InWestern European
written sources greater work efficiency is mentioned. Thus, in 1411, in the brick-kiln of Lüneburg, a brick
Ieva Ose. Building ceramics of Turaida Castle in the 13th–17th centuries