Forest glass

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Romans made of forest glass with berry soups; Germany or Netherlands, 17th century

As forest glass is called by iron oxides greenish colored potash glass , which from the Middle Ages to the early modern north (about the 12th and 17th century) of the Alps in the forest glassworks was established. Forest glass also names the corresponding epoch in glass history. Forest glass production came to an end with the rise in wood prices in the 19th century. The reason for this was the decline in forest areas and the resulting lack of fuel to operate the smelting furnaces . In the forest, where the forest glassworks were located, there were also corresponding trees and other plants for producing the potash used as glass converters and means to lower the melting temperature .

Glass manufacturing

Early glass making

As a glass former was a suitable quartz sand used, which could be reduced if possible near the cottage, for example, in streambeds stranded weathered Taunusquartzite . In contrast to Venice , where special white sand was used for the “ cristallo ”, it was necessary to use quartz sand with a small amount of silt , which was easy to melt , in the forest huts . Iron oxides were mixed in with Taunus quartzite, which color the glass green even in quantities of less than 0.1 percent.

As glass converter and means for lowering the melting temperature was used from vegetable ash in ash worldwide obtained potassium carbonate ( "potash"). Georgius Agricola names oak , beech or spruce as ideal carriers for pottery, but ferns , molasses or wool wax were also used. The processed ash was not potash in the actual sense, but pure incineration ash with all its impurities. The plant ash also provided some of the lime needed to make good glass.

The melt ran off in two steps. First the smelter mixed the raw materials (two parts by weight of ash, one part of quartz sand) into a mixture . Then the mixture was "cooked" in the frit oven at approx. 750 ° C for one day and one night to fry . The frit must be stirred as soon as it gets hot so that it doesn't melt and cake in the heat of the fire. This ash-sand mixture was put into the melting furnace as a new mixture for five hours , in which the glass was now made. The furnace was started up, the mixture was inserted, melted and refined , left to “stand” from the melting temperature of around 1200 ° C to the processing temperature and then removed. This cycle lasted about 18 hours.

After the stoker had brought the furnace to the melting temperature, the melter placed the first deposit in the ports ( crucible ), which now had to simmer until the batch portion had melted clear. The samples, which were taken regularly, showed when no more pieces of sand were visible in the glass - the mixture was "out of the sand" . The subsequent deposits in the same port were made in the same way until it was fully melted. The glass bile  - unmelted impurities floating on the surface, consisting mainly of alkali sulphates - was “skimmed off” by the smelter. The stoker now ran the furnace to the maximum temperature to begin the purification. If the thread test showed that the melt was completely clear, the glass had to "stand out" at processing temperature - the glass was ready and the stirrer went to "knock", that is, he woke the glassmaker, which could be done at any time of the day or night was. The oven temperature was kept constant for glass shaping. The “working out” took ten to twelve hours until the molten glass was shaped into the various products.

Flat glass

One of the main products of the forest glassworks was the slug panes, small round panes of glass with a diameter of 10 to 15 cm, which are thicker in the middle. This thickening, which is required for binding, is called butze . The moon glass technology came from France, more precisely from Normandy . The glassmaker blew a small ball, which was stapled, knocked off the pipe, and reheated. When the glass was softened by the heat, the stapling iron was rolled in hand. Due to the centrifugal force , the glass ball opened into a disk . In the cities the glass panes were joined together with lead rods to form windows.

Hollow glass

Wine bottle, France around 1850

From the 13th century onwards, the glassworks produced soup beakers . This form came from the Orient and probably reached the north via Venice. There were widespread late Roman forerunners of partly high quality. Nupp glasses are round cups with straight walls and a slightly protruding lip rim. They are decorated with many small glass nubs placed on the wall.

At the beginning of the 15th century, Krautstrunk  - a small, slightly bulbous cup with a few thick glass nubs - replaced the Nuppbecher. As a result, the herb stalks could be made faster and were an artistic response to the increased demand for glass vessels.

After 1500, the cabbage drink slowly developed into the Berkemeyer , a slightly conical mug that is decorated with a thread in the middle. The thread forms the dividing line between the straight, studded lower part and the smooth, conically projecting upper part. Most of the time, the foot has a plucked, slightly wavy foot ring. From the middle of the 16th century, the glass workers Berkemeyer also made with a spun, pierced base, and later with an exclusively woven base. The Berkemeyer is a more elegant appearance than the cabbage drink; its development coincided with the arrival of the Renaissance in transalpine Europe.

Romans are no longer medieval glasses, but still count as forest glasses. They have a spun, conical base, a cylindrical shaft, and a spherical cup . The shaft was mostly decorated with nubs, from 1630 also with berry nubs. To make a Roman, a higher level of craftsmanship was required, but from the 17th century forest glass was no longer the top of the art of glass.

In addition to the cups with attached glass decorations, there are also optically blown glasses. Their rib decoration is made by blowing the hot glass into a ribbed clay model as a negative mold. A second step to apply the decoration is not necessary. A technical refinement are cross-ribbed cups. Rib beakers were made from the 15th century, and in the 16th century also with feet. A typical ribbed cup is the Maigelein , a low, bulbous cup with a pierced bottom.

More vessel shapes are the thin and high upwardly conically opening rod glasses, up to two-liter cylindrical Humpen whose wall is bulged shape of a cone in the upper region and the high lobe glass.

In the forest glass there are shapes that appear under the name Kuttrolf , which is derived from Gutter (the throat ) - in the Brothers Grimm dictionary it says: “Gutter is a bottle with a wide belly and a long, narrow neck that turns into a drinking bowl expanded; a vessel shape from late antique culture. ”These bottles are rare in museums, but known from wood engravings by Leonhard Beck (1523) and Dürer's pupil Hans Weiditz (1521). The belly has a pierced bottom and the neck forms an arc of 45 ° so that they could be pushed under the belt and were always with you. The pouring bowl has the shape of a clover leaf.

The Angster is a bottle or drinking bowl with a container made with an unusual suction and blowing technique, the specialty of which is that it has a neck consisting of three to five tubes. The technology already existed in Cologne in the 3rd and 4th centuries, and multi-tube bottles have been used throughout the Middle Ages. In typical angster, the neck tubes are vertical and twisted 90 °. A loud gurgle and chuckle can be heard when drinking out of fear.

Another shape is the double-conical bottle . This has a flat bottom, a cylindrical body and a conical neck with a folded mouth. The peculiarity is that a ring is folded between the neck and the body, but its purpose cannot be identified.

Special forms of glass products were, for example, hour glasses , chafers and pilgrim bottles .

trade

The use of glass has gradually increased since the 13th century. Glazed windows were a great luxury well into the Middle Ages and only became common practice in the 16th century. The situation is similar with the use of glass drinking vessels - glass was considered to be extremely valuable and was only found in the households of the aristocrats or the wealthy townspeople .

The glass products were packed by the setters , often the wives and daughters of the glassmakers, in damp straw, which was kept moist so that it remained flexible, and loaded into humps ( called Kiepen in the north ). The glass carrier , Kraxträger , Reffträger or Kiepenkerl carried the glass with the carrier on the back over the well-known trade routes in the cities to the glass dealers ("ufftracht"). Most of the production was given to the feudal lords as taxes. The electoral trade routes were called " Goldener Steig " and connected z. B. Prague with the Fugger city Augsburg or went via Paderborn to Hameln through the Teutoburg Forest towards Berlin. The traders also picked up broken glass, which the porter took back to the hut, where it was melted down again.

Mecklenburg forest glass has been exported mainly to Holland and Hamburg since the 17th century. The goods were transported to Hamburg either from Boizenburg down the Elbe or by sea to Lübeck. Rostock was more important as a transshipment point than Lübeck. Wismar can be seen roughly on a par with Lübeck. A lot of glass was also exported to Scandinavia from Lübeck and Wismar. In the 18th century, sales to Denmark, Riga and St. Petersburg and even to North America, the latter in particular for bottles in square shape with very strong glass, were important.

Forest glassworks

Forest glass or traveling glass works were a specific form of operation for the production of glass in Central Europe from the Middle Ages to the early modern period . In the Middle Ages, in addition to the sedentary monastery huts , which were limited to the production of colored flat glass for church windows , there were also “secular” hikers' huts. After the collapse of the oriental trade in the early Middle Ages, the soda needed for glass production had to be replaced by locally produced potash from the Levant coast and Egypt due to the supply difficulties. Because of the high demand for wood, the glassworks were located in the woods, mostly in a less populated area; so in the Thuringian Forest , Weserbergland , Kaufunger Forest , Bohemian Forest , in the southern Ore Mountains , in the Fichtel Mountains , Spessart , Black Forest , in Lorraine , Alsace , the Ardennes , Mecklenburg and also in Holland .

Although there was glass production before that, Emperor Charles IV , who, along with other craftsmen, also brought glassmakers from Italy and France to Prague, played an important role in the development of forest glass. From Bohemia the glassmaker clans migrated further and further west.

For the liege lord, the glassworks was not just a glass producer who brought in considerable taxes. Because of their high wood consumption, they also had important tasks in land development and forest management . When the forest was cut, the forest glassworks migrated to more and more distant, unpopulated areas up to the high valleys, and with them went the whole entourage that they employed.

At that time, about 1 cubic meter of wood was required to produce 1 kg of glass . The wood requirement of a single glassworks for the production of potash and for heating the glass ovens was 2000 to 3000 solid cubic meters of wood annually , which corresponds to an amount of about 3000 to 5000 cubic meters. For a glassworks, the wood supply of around 20 to 30 hectares of forest was required annually. 80 to 85% of the wood was incinerated for potash extraction. As early as the 14th century there were complaints about the forest devastation caused by the glassworks; In the Spessart, for example, there were never more than 10 forest glassworks in operation at the same time. For the landlord, however, a glassworks was the most lucrative way of exploiting his forest.

Farmers and cattle breeders could settle in the abandoned dwellings , who in turn produced food on the deforested areas and thus further promoted growth. A hiking glassworks was able to prepare entire forests for settlement , farm after farm, settlement after settlement. In some areas the use of wood in glass furnaces was forbidden as early as the 17th century (England 1615, Bohemia 1650), which heralded the end of forest glassworks.

Hut building

Oven remains of the glassworks on the Emsbach Gorge

For a forest glassworks, all the structural systems for the ironworks first had to be created. Often more than ten families lived together in a forest glassworks, which required a not inconsiderable infrastructure. Since the glassworks only operated for a limited period of time, most of the buildings were not very massive.

The central building was the hut building, in which the melting furnace and cooling furnace stood. The floor of the hut was made of clay . The building was a long shed made of wood with a smoke roof typical of glassworks, through which the smoke rising from the stove pulled out of the hut. There was a wooden work platform around the furnace on which the glassmakers stood while they worked. Firewood, potash and sand could also be stored dry in the hut building. Furthermore, finished glassware was prepared for dispatch. If the glassworks was on a stream, a mill with a stamping mill could be built, which made the work much easier.

The apartment of the hut master were slightly better built homes where the glassmakers join lived with their families. The other workers lived in small cottages .

With increasing prosperity, stables and barns were built for agriculture. The surrounding areas were used for agriculture in forestry for the self-sufficiency of the hut staff. When the soil was exhausted, the fields were left to grazing cattle until the soil recovered.

oven

The fryer
Melting and cooling furnace

According to figurative sources, the glass melting furnaces of the forest glassworks were usually three-story round furnaces. They were egg-shaped constructions made of clay bricks mixed with fired chamotte , 3 m in diameter and up to 3 m high. The firing room was on the lower floor with one or two semicircular openings for wood to be thrown in.

In the middle the flames broke through a large round opening into the second floor, where the harbor ovens were located. This approximately 1.20 m high room was provided with oven doors measuring 20 × 20 cm all around, through which the mixture could be inserted and the glass removed.

The cooling furnace, which was only 400 ° C, was located on the upper floor, which was connected to the melting room through a small opening. The cooling furnace was provided with a small opening through which finished workpieces were inserted. In the evening the hole between the melting room and the cooling room was closed with a stone so that the glass could slowly cool down overnight.

Archaeological excavations in medieval and early modern glassworks often show a different picture. Accordingly, it is more of a horizontal oven that was functionally divided. This scheme can also be found in modern huts.

Tools

Glassmaker's tools
  • The glassmaker's pipe (A) is a pipe about four feet long, half made of iron and the other half of wood. The iron end was immersed in the glass bath. A certain amount of glass was taken up by turning and shaped into a ball by blowing into the wooden end.
  • The staple iron (B) was a four-foot long stick that was also made half of wood and half of iron. A small amount of glass was picked up with it and glued to the bottom of the cup, or knobs and threads were added.
  • The Auftreibschere (D) consists of two knife-shaped tips which are connected to a spring clip. It is used to cut or blow up glass.
  • The beaked scissors (C) are scissors with small blades and long handles that are used to cut the glass.
  • The clamp iron (E) is a type of tweezer with a wide handle and pointed or flat ends.
  • The optical shapes (bottom right) are hollow clay shapes that can be round, triangular or square and have flat or jagged inner walls. With them the ribs are pressed into the glass.

Hut people

Until the 18th century the owners of the smelters were independent entrepreneurs. They signed a fixed-term contract with a landlord about the use and deforestation of a piece of forest, the keeping of goats, pigs and cows that were also allowed to graze in the forest, and so on. Within their glassworks they were the absolute rulers . At the same time, the owners of the smelter were glassmasters and since 1406 ( guild regulations from the Spessart) they have been properly connected. The success of a metallurgical company depended largely on the skill of the glass master, but also on his business acumen. Shifts were worked around the clock in a forest glassworks . According to a glassmaker's regulation, the annual production time was limited from Easter to St. Martin's Day in November. Repairs to the stoves were carried out in winter and fuel was obtained for the next year.

A work space consisted of masters , prompter , beginners and the girder .

The blower took a chunk of glass out of the furnace with a pipe and, depending on the workpiece, blew the goblet in a clay mold or freehand to the preform. Then he passed the pipe on to the master, who finished the glass. To do this, he had the beginner bring him lumps of glass, which he attached to the cup and formed into knobs and threads or used for stitching. When the glass was stapled, the master opened it. The single carrier brought the finished glass into the cooling furnace.

There was a strict hierarchical order - advancing from one post to the next could take years. So the one-man was only allowed to practice during the breaks at the Glasholen ("glass tinkering"). If he had learned to fetch glass over time, he became a beginner, he “got into the stove”.

The smelter knew the secret glass recipes and the raw materials that were needed for them. He mixed the raw materials into a mixture, filled it into the ports and was responsible for the success of the melt.

The Strecker was a specialist in the manufacture of flat glass (window glass).

The port maker built the furnace, struck and changed ports.

The Schürer was responsible for heating the ovens. There was a day cooker and a night cooker who brought the desired temperature into the ovens. The temperature was measured by color or by feel.

The potash boiler burned the wood to ash and processed it into potash, which served as a flux for the glass melt.

The glass miller crushed the quartz rock and the frit in the stamping mill .

The lumberjacks cut the wood, took it to the stove, chopped it and stored it to dry. The heat in the oven ensured quick drying.

The personal history of these glassmakers from 1409 to 1820 is documented for an important geographical area and published in the Werra-Weser-Bergland glassmaker family book.

Examples of forest glassworks

literature

swell

literature

  • Georg Landau : History of the glassworks in Hessen. In: Journal of the Association for Hessian History and Regional Studies. Volume 3, 1843, pp. 280-352. (1st facsimile reprint in: Georg Landau: Geschichte der Glashütten in Hessen and other contributions. Edited by Dieter Carl. Historical Edition Carl, Vellmar 2001, ISBN 3-9806580-7-4 ) (digital copy of the original edition)
  • Hans Löber: Guttrolfe, shaping and manufacturing technology. In: Glass technical reports. Volume 39, H. 12, 1966, ISSN  0017-1085 , pp. 539-548.
  • Claus Grimm (Ed.) : Happiness and Glass. On the cultural history of the Spessart glass (= publications on Bavarian history and culture. Volume 2). Verlag Kunst & Antiquitäten, Munich 1984, ISBN 3-921811-34-1 .
  • Werner Loibl : The Kurmainzische Spiegelmanufaktur Lohr am Main (1698–1806) and the successor companies in the Spessart. 3 volumes. History and Art Association Aschaffenburg, Aschaffenburg 2012, ISBN 978-3-87965-116-0 , ISBN 978-3-87965-117-7 , ISBN 978-3-87965-118-4 .
  • Erwin Baumgartner: Glass of the late Middle Ages. The Karl Amendt Collection. Kunstmuseum Düsseldorf, Düsseldorf 1987, DNB 880766794
  • Erwin Baumgartner, Ingeborg Krüger: Phoenix made of sand and ashes. Medieval glass. Klinkhardt u. Biermann, Munich 1988, ISBN 3-7814-0280-0 .
  • Axel von Saldern : glass. Antiquity to Art Nouveau. The collection in the Museum of Art and Industry Hamburg. Arnold, Stuttgart 1995, ISBN 3-925369-42-2 .
  • Barbara Scholkmann : Glass production in Central Europe in the Middle Ages. Questions and results of archaeological research. In: Sönke Lorenz , Michael Matzke (Hrsg.): Siedlungsgeschichte und Waldnutzungsformen (= Freudenstadt contributions to the historical regional studies between Neckar, Murg and Kinzig. No. 10, ZDB -ID 353838-2 = publication by the Alemannic Institute. No. 64). Heimat- und Museumverein für Stadt und Kreis Freudenstadt, Freudenstadt 1997, pp. 113–136.
  • Danièle Foy: Le verre médiéval et son artisanat en France méditerranéenne. CNRS Editions, Paris 2001, ISBN 2-271-05989-5 .
  • Walter Lang: Late medieval glass production in Nassachtal, Uhingen, Göppingen district (= material booklets on archeology in Baden-Württemberg. H. 59). Theiss, Stuttgart 2001, ISBN 3-8062-1569-3 .
  • Hermann Junghans, Jürgen Lewerenz, Volker Janke: Forest glass in Mecklenburg. Thomas Helms Verlag , Schwerin 2010, ISBN 978-3-940207-61-6 .
  • Verena Kaufmann: Archaeological finds of a late medieval glass workshop in Bad Windsheim (= publications and catalogs of the Franconian Open Air Museum . Volume 59; = Sources and materials for house research in Bavaria. Volume 14). Franconian Open Air Museum, Bad Windsheim 2010, ISBN 978-3-926834-74-4 . (Dissertation University of Bamberg 2010)
  • Ralf Wendt: Glassworks in Mecklenburg. Contribution to the social history and folklore of a rural branch of industry (1st half of the 17th to the end of the 19th century). Berlin 1968, DNB 481495681 . (Dissertation at the Humboldt University Berlin September 30, 1968)

Web links

Commons : Waldglas  - Collection of images, videos and audio files
Wiktionary: Waldglas  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Forest glass in Mecklenburg. 2010, p. 11.
  2. ↑ Irmgard Müller: An ignored Speyer medicine tax of the 16th century. In: Werner Dressendörfer, Wolf-Dieter Müller-Jahncke (Ed.): Orbis pictus. Cultural and pharmaceutical historical studies. Frankfurt am Main 1985, pp. 187-215; here: pp. 190 and 212.
  3. ^ Forest glass in Mecklenburg. 2010, pp. 10-11.
  4. ↑ Klaus Kunze: Glasmacher-Kippenbuch Werra-Weser-Bergland from the early modern era to the beginning of industrialization around 1820. HeiKun, Heimatkundlicher Verlag, Uslar 2000, ISBN 3-933334-10-1 .
This version was added to the list of articles worth reading on October 9, 2006 .