Glass loop (production facility)

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A glass loop was a pre-industrial production facility for the manufacture and processing of flat glass . The flat glass, which was produced up until the 19th century, was initially opaque or wavy and could only be made transparent and flat by grinding and polishing. Another production branch of the glass loops was the mirror loops, there the flat glass was processed into mirrors in a further production step .

history

In the late Middle Ages, the Upper Palatinate was an important center for iron ore extraction and smelting in Europe because of its rich iron ore finds (see also Mining in the Upper Palatinate ). As a result of the Thirty Years' War , many iron hammers were destroyed and lay desolate, the iron ore deposits were also less productive and the forests were heavily cut down, so that there was no longer any available amount of charcoal , which was necessary for the operation of ore processing. For this reason, many hammer mills were converted into other operations (e.g. mills , sawmills or glass grinding) in order to continue to profitably use the water power with which a hammer was operated. At the beginning of the 20th century there were 207 grinding and polishing plants in the Upper Palatinate.

In addition, near the traditional ore deposits, brown stone and iron stone mixed with silica was found that could be processed into emery for the glass cutters . Such camps were for example at Chammünster (Raseneisenstein), at Roding ( alum-containing clay seams), Woppenrieth at Bleystein ( Eisenstein ) or Erbendorf ( Hornblendschiefer ). These rocks were ground to a fine flour, the residue of which could be used as a polishing agent after sludging (so-called "Upper Palatinate emery").

Glass casting table

Production method

The raw glass was first made in a glassworks ; in the past, a glass cylinder was blown, which was then cut lengthwise and knocked flat. Since the end of the 17th century, the glass was made on a casting table using the casting process, later the drawn glass process was added, in which the liquid glass pulp was pulled up with an iron board and then smoothed with a roller. The glass plates had a size between 47 × 78 cm up to 120 × 160 cm. This flat glass still had severe unevenness. In the grinding and polishing plant, these plates were then ground flat using the cylindrical grinding process; after this treatment, the glass looked like milk glass . It then had to be pretreated with fine sand by the workers, then it was sanded with an emery compound and treated with polishing red (iron oxide mixed with water). The pretreatment took 1/2 hour for each side, the polishing time was then about 12 hours, after which the glass was polished by hand.

Iron plates formed the base for the polishing table. Ground plaster of paris was applied to this, then the panels were placed on top. On the polishing table, blocks of felt, which were driven by water power via a shaft, rotated over the glass surface with an emery agent and water. This could be used to produce milky, polished or clear flat glass. The lubricant, also called Potte , Polierrot or Potée , consisted of iron oxide . The plaster of paris used could be reprocessed and reused. The polish turned the building, tools and clothing of the polishers red. The damaging effects on the environment (e.g. fish deaths) of the grinding and polishing works were recognized.

Up to several hundred polishing tables were used in a glass loop. After the end of the polishing process, the glasses were held in the black- painted glass chamber against a 30 cm wide gap and checked for defects, matt areas (so-called mats ) had to be reworked. Then the glass plates were provided with paper inserts and packed in wooden boxes filled with straw or wood wool and shipped.

During the further refinement of the flat glass to mirror glass, the cut glass was coated with a silver or mercury layer. Half of the total production of mirror glass in the Upper Palatinate went to the USA in the 18th century. In 1884, 7,000 people were working on 20,000 polishing blocks in Bavaria. In the years 1850 to 1890 this branch of industry experienced its heyday.

The end of glass grinding came with the modern flat glass production (drawn glass process ) at the beginning of the 20th century, which led to an industrially manufactured flat and transparent glass.

Former glass mills and glass mill museums

"Alte Schleif" Münchshofen
Former company building of the Ettmannsdorf hammer mill
Hammerhaus Groebenstaedt
Modern production plant for flat glass
  • Glass loop Münchshofen : This listed building is located in the Münchshofen district of Teublitz and is a glass grinding and polishing plant that was created in 1890 from a hammer mill . The company was last run as a sideline as a so-called “farmer's loop” and was not closed until 1953.
  • Glass loop in Neuses von Roßtal in the Fürth district : Glass loop created around 1768/69 and operated until around 1860.
  • Glass bow in wine ornaments : built at the beginning of the 18th century and existed until the first half of the 19th century.
  • Glass loop in Arnoldsreuth near Pullenreuth : As a museum with water wheels on the lower and upper glass loop and restored water inlet, the glass loop is open to the public.
  • Glass loop in Röhrenhof near Escherlich : The hammer mill, which had existed since 1433, was converted into a glass loop at the end of the 1860s. In 1934 this was converted into a mineral grinder.
  • Rear hammer to Röhrenhof (see above): The hammer, built in 1734, was converted into a glass loop and polishing unit in 1854. In 1883 it was turned into a mirror glass factory.
  • Glass loop Gebhardsreuth : In 1749 the existing mill and saw at Gebhardsreuth was converted into a glass loop.
  • Glass loop from Hofmark Grub near Grafenwöhr : An iron hammer has been in existence here since the beginning of the 16th century, which was converted into a glass loop in 1751. This glass ribbon ceased operations in 1931.
  • Spiegelschleife (Dresden) : An iron hammer stood here around 1700, which was replaced by a gemstone grinding and polishing mill in 1712 and converted into a mirror loop in 1715,largely destroyedin the Wars of Liberation in 1813.

In the Upper Palatinate there are said to have been 80 hammer mills converted into glass or mirror loops; such were, for example, in Traidendorf , Rohrbach , Deuerling , Ettmannsdorf , Hopfau , Pechhof , Plechhammer , Hammertiefenbach , the Hammer zu Gröbenstädt , Lukahammer near Oberviechtach or the Hammer zu Obermuggenthal . The Baumhof loop of the Ostbayern Mining and Industry Museum in Theuern Castle is the last mirror glass factory in Eastern Bavaria that shows the technique of glass grinding and polishing.

literature

  • Gabriele Sturm: The glass loops in the Altlandkreis Burglengenfeld . In: Annual volume on culture and history in the Schwandorf district. 4th Volume, 1993, pp. 94-114.
  • Johannes Ibel: The mirror glass grinding and polishing in the district of Neustadt an der Waldnaab including the city of Weiden. A contribution to the industrial and economic history of the northern Upper Palatinate. eurotrans-Verl., Weiden in der Oberpfalz 1999.

Web links

Individual evidence

  1. ^ History of mirror production
  2. ↑ Karl-Heinz Preißer: The Hofmark Wildenau in the Course of History (2nd edition). eutrans-Verlag, Weiden 1992, ISBN 3-929318-00-8 , p. 66.
  3. ↑ Klaus Ibel: Amesriet and Braunetsrieth - two clearing locations with reference to iron extraction. In: Vohenstrauss local history working group: Forays. 20th year, issue 27, 2005, pp. 141–164.
  4. ↑ Sturm, 1993, p. 94.
  5. ↑ Sebastian Schmidmeier: The history of the mill in Deuerling. Laßleben, Kallmünz 2010, pp. 46–47. ISBN 978-3-7847-1222-2 .
  6. ↑ Johannes Ibel, 1999, p. 23.
  7. ↑ Johannes Ibel, 1999, p. 17.
  8. ↑ Landsassengut Gebhardsreuth - grinding and polishing works at Tröbesbach
  9. ↑ glass loop Teublitz-Muenchshofen
  10. ↑ Martin Mannewitz: Münchshofen, former grinding and polishing plant. In: Yearbook of Bavarian Monument Preservation. Bavarian State Office for Monument Preservation, Munich 2006. ISSN  0341-9150
  11. ^ Dieter Koerber: Beginnings of industrialization in Roßtal.
  12. ^ Dieter Koerber: Beginnings of industrialization in Roßtal.
  13. ↑ Glass grinding in Arnoldsreuth
  14. ^ Hammer mills in Röhrenhof
  15. ↑ Landsassengut Gebhardsreuth
  16. ↑ The Hofmark Grub
  17. ↑ Weißeritzmühlgraben in Dresden ( Memento of the original from February 14, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.weisseritzmuehlgraben.de
  18. ^ Reinhard Dähne & Wolfgang Roser: The Bavarian Iron Road from Pegnitz to Regensburg. House of Bavarian History , Volume 5, Munich 1988, p. 47.