Glasswort

Glasswort

[glas-wurt, -wawrt, glahs-]
The common name Glasswort came into use in the 16th Century to describe plants growing in England whose ashes could be used for making soda-based (as opposed to potash-based) glass. The glassworts are succulent, annual "halophytes", or plants that thrive in saline environments, such as seacoasts and salt marshes. While the original English glasswort plants belong to the genus Salicornia, the term has been extended over the years to halophyte plants from several genera, some of which are native to continents unknown to the medieval English, and growing in ecosystems such as mangrove swamps never envisioned when the term glasswort was coined.

The ashes of glasswort plants, and also of their Mediterranean counterpart saltwort plants, yield soda ash, which is an important ingredient for glassmaking and soapmaking. Soda ash is an alkali whose active ingredient is now known to be sodium carbonate. Glasswort and saltwort plants sequester the sodium that they absorb from salt water into their tissues (see Salsola soda). Ashing of the plants converts some of this sodium into sodium carbonate (or "soda," in one of the old uses of the term). The sodium carbonate can be purified by washing ("lixiviating") the ashes and boiling the solution dry.

The appearance of the word glasswort in English during the 16th Century is reasonably contemporaneous with a 16th Century resurgence in English glassmaking, which had suffered a long decline after Roman times. This resurgence was led by glassmakers who emigrated to England from Lorraine and from Venice. The Lorraine glassmakers brought with them the technology of Waldglas, the greenish glass that utilized potash from wood ashes as a flux. The Venetian glassmakers brought with them the technology of cristallo, the immaculately clear glass that used soda ash as a flux. These glassmakers would have recognized Salicornia europaea growing in England as a source for soda ash. Prior to their arrival, it was said that the plant "hath no name in English."

By the 18th century, Spain had an enormous industry producing soda ash from saltworts; the soda ash from this source was known as barilla. Scotland had a large 18th century industry producing soda ash from seaweed. The soda ash from this source was known as kelp. This industry was so lucrative that it led to overpopulation in the Western Isles of Scotland, and one estimate is that 100,000 people were occupied with "kelping" during the summer months. In the same period, soda ash (la soude de Narbonne) was produced in quantity from glasswort proper around Narbonne, France. The commercialization of the Leblanc process for synthesizing sodium carbonate (from salt, limestone, and sulfuric acid) brought an end to the era of farming for soda ash in the first half of the 19th century.

Glasswort Species

Plants that have been called glassworts include:

References

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