page_title: Early modern glass in England
section_title: Chemical composition
hierarchical_section_title: Early modern glass in England / Chemical composition
context_page_description: The early modern period in England brought on a revival in local glass production. Medieval glass had been limited to the small-scale production of forest glass for window glass and vessels, predominantly in the Weald. The organisation of production evolved from the small-scale family-run glass houses typical of forest glass-making to large monopolies granted by the Crown. The influx of immigrants from Europe brought changes in furnace technology and raw materials, creating a better quality glass. Monastic decrees later banned the use of wood fuel which was then replaced by the less expensive alternative of coal. The development of lead glass in the late 17th century propelled England to the forefront of the glass industry and paved the way for advancements in the Industrial Revolution.
context_section_description: Glass has three major components: a network former (silica), a network modifier (flux), and a network stabilizer (predominantly lime). In the early 16th and 17th centuries glassmaking (the manufacture of glass from raw materials) and glassworking (the creation of objects from glass) occurred within the same glasshouse. Glass was also recycled at this time in the form of cullet.
  In the early modern era, network formers were obtained from fine or coarse sands which were usually located near the area of production or from silica based pebbles.
  Network modifiers were used to alter the chemical composition of the network former and reduce the melting temperature of the batch. These fluxes varied depending on the type of glass. Potassium oxide (K₂O) based alkalis were used extensively in glass production.
  
  The type of flux selected heavily influenced the quality of the glass produced. In England, beech wood and oak were preferred for forest glass. For soda-lime glass (Na₂O), alkalis were often found in the form of marine plants – either local kelp or imported plants from the Mediterranean and the Near East (barilla, polverine, rochetta, sevonus, natron). 
  These were often used for the production of 'white' crystallo glass, a colourless glass or façon de venise, colourless glass of the highest quality.
  Network stabilizers in early modern England continued to be lime sources. Lime occurs as a natural contaminant in most sands, and may also be intentionally added to the melt.
caption: Halogeton sativus is one of the plants from which barilla was made. The species was formerly classified as Salsola sativa. Engraving published 1813 (Adolphus Ypey).
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