Laughing In the Fern

Fern ash is high in potassium carbonates. If carefully purified it can make an exceedingly clear glass, rivaling or even surpassing Venetian cristallo. It has the additional advantage of being physically tough, making it ideal for engraving or diamond-point work. On the other hand, once out of the furnace it stiffens quickly, giving it a short 'working life' for the hot glass artisan. This limits designs to simple basic forms. While soda-based glass was the norm for the Mediterranean region, throughout the Middle Ages and into the Renaissance, northern Europeans were more likely to be making potash-based glass. They utilized the potassium rich local trees and plants of the northern forests. In France, fern glass is called verre de fougère. In the considered opinion of some connoisseurs, wine tasted better when sipped from verre de fougère cups, hence the delightful expression 'le vin rit dans la fougère' [wine laughs (sparkles) in the fern].

Since the middle ages, fern glass became part of everyday life in northern Europe. It was familiar enough to find its way into literary verse on matters of the heart. There is a nice reference to fern glass by Geoffrey Chaucer, in The Squires Tale:

But notwithstanding, some said that it was
Wondrous to make fern-ashes into glass,
Since glass is nothing like the ash of fern;
But since long since of this thing men did learn,

Chaucer, in turn, borrowed this reference from an epic twenty-two thousand line French poem from the late thirteenth century, when the technique of making glass from ferns was already ancient.