Forest Glass

Forest glass (or 'Waldglas') is the term used to describe the transparent, greenish-bluish-grey glass that was manufactured and blown in the central European region during the medieval period. An example of forest glass is shown here:

Photo by Christine Brandel

Shown is a prunted beaker with a foot and stem. Notice the greenish color of the glass. This was the result of iron oxide occurring in the glass batch. It distinguishes the glass made in the central and northern regions of Europe from the glass made in the Mediterranean, and southern Germany, Switzerland and Italy. The heavy forestation of the regions where waldglas was manufactured contributed to the color of the glass -- trees were used for fuel to run the furnace, and the sand from this area used in the glass batch contained the iron oxide that colored the glass green. This glass was also considered a potassium-lime glass, meaning that the chemical components that made up this glass included silica (sand), potassium carbonate (derived from wood ashes), and lime. This is different than soda-lime glass, which was made in other regions and included silica, lime and sodium oxide. Potassium-lime glass is harder, more resistant to breakage, and can be engraved and wheel-cut. It's also more brilliant, but it changes state from molten to solid more rapidly, and thus must be worked more quickly.

Here's another example of forest glass:

Photo by The Allaire Collection

Personally, I love the color of this type of glass. In later years, it was discovered that adding manganese oxide to the glass batch would result in a colorless glass, but I have always had a love for the deep foresty green of the glass of this period.

The Aldrevandin Beaker

In the British Museum collection, there is a beautiful vessel from the end of the 13th century called the 'Aldrevandini Beaker'.

photo: British Museum

It's a blown glass beaker with enameled decoration, and an inscription that tells us who the maker was, a master called Aldrevandin. The enameled inscription on the vessel reads: "MAGISTER ALDREVANDIN ME FECI", and translates to "Master Aldrevandin Made Me". It's not often that a glass item is actually 'signed' by it's maker!

What's really interesting about this piece is that the enameling is done both inside and outside the vessel, as opposed to just the outside. There was discussion among historians, too, as to its origin, seeing as how many Syrian and Islamic vessels are also enameled very richly, and this one was found in Europe. Ultimately, three points allowed historians to determine that the vessel was made in Venice -- the shape is not the same as Syrian or Islamic beakers, this being more straight-sided than those typically made in the medieval Islamic world, the enameling is done on interior and exterior surfaces, as opposed to just the exterior, and the enamels used included yellow, instead of gold, enamel. Syrian and Islamic vessels were enameled with gold, only on exterior surfaces, and were typically shaped with a taper from the base to the rim.

Additional fragments of vessels such as this one were found in Europe, which allowed historians to conclude that this vessel was most likely not made in the Islamic region, but in Venice. At the time of this vessel, the Venetians did possess the knowledge and skill to make beakers such as this one.

In a future post, I'll write about what I've learned about how this vessel was likely made.