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Medieval Forest Glass: Materiality, Affect, and the Environment

Updated: Oct 13, 2019

by Stephanie Trigg

Green glass beaker with prunts
Beaker (Krautstrunk), Germany, Rhineland, 1425-1525, Victoria and Albert Museum. Image reproduced with permission.

In Chaucer’s Squire’s Tale, the people of Cambyuskan’s court ponder the mysteries of glass-making:

… somme seiden that it was

Wonder to maken of fern-asshen glas,

And yet nys glas nat lyk ashen of fern

[Some said it was a wonder that glass is made from the ashes of ferns, since glass does not resemble fern-ash.] The Squire’s Tale, lines 253–5

But this wonder is also very familiar. The Squire goes on:

But, for they had yknowen it so fern,

Therfore cesseth hir janglyng and hir wonder.

[But because they had known this for so long, they cease[d] their chattering and their amazement.] The Squire’s Tale, lines 256–7

Chaucer draws on a similar passage in Le Roman de la Rose, where the process of glassmaking is likened to a form of alchemy. Even everyday glass can provoke such wonder about its materiality, whether this be the transformation of gritty or powdery substances such as sand and ash into the shiny hard surfaces of glass objects; the combination of human breath with the molten malleability of hot glass in the glassblower’s craft; or the ever-present capacity of glass to crack or shatter, a capacity that always frames the way we hold and use glass objects.

Jonathan Gil Harris writes about the various forms of temporality invoked, or provoked by materiality, or by material objects. An object’s multi-temporality comes to the fore when it provokes reflection on “the relations between now and then, old and new, before and after.” If we think about the formation of glass objects, their complex temporality becomes more readily apparent. Whether twisted or blown by human breath, or poured into moulds by mechanised processes, or floated on baths of molten tin to make sheets for windows, the formation of glass always marks a kind of temporal pause in a physical transition from something moving to something in fixed form.

Glass, then, is a form of temporal archive; and indeed, it is not so much a kind of material as a “state of matter.” Its molecular structure is described as a “disordered solid” or a “rigid liquid”: its atoms are held firmly in place, but their form is random, not neatly ordered. In northern medieval Europe, the quality of glass declined after the shrinking of the Roman Empire. From the thirteenth to the seventeenth century, the glasshouses of Europe produced tableware, windowpanes, and storage vessels, but in glass that was often thicker and less pure or clear than Roman or Venetian glass. This European glass had a much higher proportion of ash from organic matter such as ferns, bracken or beech trees. Beech is the material recommended by Theophilus Presbyter in the oldest surviving manual of glassmaking. He mentions “oak and beech … but also reeds, wheat and barley straw, pea stalks and thistle.” Ash from these plants, or ferns, is added to sand or silica to lower the temperature at which the sand will melt.

Medieval “forest glass”, made in this way, was often green in colour, because of the iron and manganese in the sand. The “greenness” in the name of this glass suggests something more organic, however, as if something of the greenness of trees and forests were preserved in the making of glass. Indeed, medieval glasshouses were often set in the forests, close to beech trees and forest bracken. But of course, it took a tremendous amount of beech to produce enough ash to make glass in any quantity, while the beech trees were also used as fuel to fire the kilns at very hot temperatures. Ironically, the making of “forest glass” in this way is actually unsustainable, as it consumes and destroys the forests themselves. In England, this medieval industry was restricted in 1615 for this reason, and glassmakers turned to coal to fire their ovens.

The example above from the Victoria and Albert Museum features the “cabbage” design that was very popular in the German style of glass-making. These projecting bosses or “prunts” of glass — sometimes they are shaped in the form of bunches of grapes — seem to have been designed to stop greasy fingers slipping over the surface of the glass and dropping it. This is one of the material ironies of glass manufacture: the more the craftsman succeeds in refining and purifying the techniques of glassmaking and glassblowing, the more vulnerable is his work to the vicissitudes of everyday use.

This style of drinking glass or beaker was enduringly popular in Germany, well into the eighteenth century and beyond, and it is now available in the form of medievalist reproductions. Whether these are machine-made or in the words of the “Merchant Venturers” website, “crafted using traditional methods that have been handed down from one generation to the next in Bohemia (Czech Republic)”, these examples of medievalist reproduction feed the modern desire to see and touch the medieval as “primitive,” or at least, as pre-industrial, or handmade, a position that tends to idealise medieval manufacturing as more “authentic” especially in an era of mass production. As drinking vessels, these items also invite us to feel and touch the experience of medieval drinking.The more I work on, think about, look at medieval glass, the more complex and subtle it seems to me as a form of materiality and temporality. I began this post with a textual example. Coming from medieval literary studies, that is where I feel safest, with my experience mediated through words. For me, the challenge of thinking about material objects is been eased, somewhat, by the familiar resonances of medievalism, the re-creation of medieval culture: the desire to apprehend, as directly as possible, some kind of “touch” of the medieval.

Further Reading

Jonathan Gil Harris, Untimely Matter in the Time of Shakespeare (Philadelphia: University of Pennsylvania Press, 2011)

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