In the decoration of this green glass recourse was had to the old methods of threading, but above all to the more or less circular projections or bosses of varied forms that are found scattered over the sides. These are technically known as ‘prunts’—the _nuppen_ of the Germans. We have had something to say of one special form of these protuberances when describing the glass of the Anglo-Saxons.[186] These prunts fall into two groups: the _stechel-nuppen_ or thorned prunts, of which the old Franco-Saxon form is an extreme type; and the _beeren-nuppen_ or berry prunts, derived possibly in the first case from the moulded reliefs of bunches of grapes that we find so often on Roman glass. A third group might perhaps be made for another classical form where the projections take the shape of a medallion—a head stamped on the surface of the prunt while it is still soft. These _nuppen_ had a practical use,—so Mathesius, a contemporary writer, tells us.[187] They were to prevent the glass from slipping between the fingers of the drinker. With a similar object—for the _insertion_ of the fingers in this case—these prunts are sometimes reversed, forming deep pits in the sides of the vessel. There is a late example of this form at South Kensington and another in the British Museum. The _stechel-nuppen_ may assume less aggressive forms; the points may be smoothed down while the metal is soft, and we then have merely a series of disc-like thickenings on the sides of the glass. By this means, as in the more refined Dutch _roemer_ of the seventeenth century, effects of great beauty, due to the varying transparency of the glass, were obtained. In colour this Rhenish glass may vary from a greenish-blue to a pale bottle-green, or again to a deep, almost black, tint of olive-green or violet. It is from glass of this description that the pale-coloured wines of the country have been drunk, perhaps without break, from late Roman times. This it is, as well as the fact that it has never been decorated with enamel, and rarely, in Germany at least, by the wheel or with the diamond, that has given to the green prunted glass of this family a position apart. I have called this glass Rhenish, inasmuch as the centre of the manufacture seems to have been around Cologne, whence some of it found its way down the river to the Low Countries, along with the wine that was drunk from it; but much green glass was, we know, made also in the Netherlands.