![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
medieval glassmaking!
Nov. 24th, 2004 06:10 pmAccording to the Corning Museum of Glass
http://www.cmog.org/index.asp?pageId=1002&mid=mi28
(DIRECT QUOTE from article:)
"The essential raw materials for making glass are soda, lime, and silica (collectively known as ‘batch’). Sand is the source of the silica that makes up about 70%. Soda (about 15%) was added to reduce the temperature at which the sand melted. Lime (about 8%) makes the glass chemically stable. The remaining 7% consist of impurities and sometimes of additives to change the colour of the glass. It sounds improbable, but seems to be true, that most early glassmakers were unaware that lime was a necessary ingredient; they introduced it by accident, mixed with the sand or the soda.
In Roman times, the preferred source of the sand (according to Pliny) was the beach at the mouth of the Belus (Na’aman) River near Akko, Israel. There, the sand contains quantities of broken shells, and these provided the lime necessary to stabilise the glass. Roman and early medieval glassmakers in the Levant used a mineral form of soda (natron), which they imported from Egypt. During the 9th century, however, they began to use soda derived from the ashes of halophytic plants, which grow locally. The plant ash also contained lime and, since too much lime ruins the glass, this must have compelled glassmakers to use sand with a reduced amount of shell, or crushed quartz pebbles, or to purify the plant ash. Nevertheless, in the decades around AD 1200, two eyewitnesses, William of Tyre and Jacques de Vitry, noted that glassmakers used sand from the beaches of Akko and Tyre. How the medieval glassmakers reduced the amount of lime in their plant ash to compensate for the lime in the sand, is not yet known."
http://www.cmog.org/index.asp?pageId=1002&mid=mi28
(DIRECT QUOTE from article:)
"The essential raw materials for making glass are soda, lime, and silica (collectively known as ‘batch’). Sand is the source of the silica that makes up about 70%. Soda (about 15%) was added to reduce the temperature at which the sand melted. Lime (about 8%) makes the glass chemically stable. The remaining 7% consist of impurities and sometimes of additives to change the colour of the glass. It sounds improbable, but seems to be true, that most early glassmakers were unaware that lime was a necessary ingredient; they introduced it by accident, mixed with the sand or the soda.
In Roman times, the preferred source of the sand (according to Pliny) was the beach at the mouth of the Belus (Na’aman) River near Akko, Israel. There, the sand contains quantities of broken shells, and these provided the lime necessary to stabilise the glass. Roman and early medieval glassmakers in the Levant used a mineral form of soda (natron), which they imported from Egypt. During the 9th century, however, they began to use soda derived from the ashes of halophytic plants, which grow locally. The plant ash also contained lime and, since too much lime ruins the glass, this must have compelled glassmakers to use sand with a reduced amount of shell, or crushed quartz pebbles, or to purify the plant ash. Nevertheless, in the decades around AD 1200, two eyewitnesses, William of Tyre and Jacques de Vitry, noted that glassmakers used sand from the beaches of Akko and Tyre. How the medieval glassmakers reduced the amount of lime in their plant ash to compensate for the lime in the sand, is not yet known."
