Sunday, October 2, 2011

Core-Formed Vessels

Photo by Christine Brandel

Okay, so this is not technically glass from the medieval period, but I did say at the outset that sometimes I would veer off into other periods, particularly the early ones. Okay, I sorta said that. But anyway.

So! The Allaire Collection posted recently about one of their core-formed vessels, and that's what inspired my post today. I have a soft spot in my heart for core-forming. It was one of the first techniques I tried to replicate using period materials and processes, way back about seven or so years ago in the pursuit of projects as a member of the SCA. My experiments were not extremely successful, but they were educational, at least.

What is core-forming?

Basically, the technique of core-forming applies to making hollow vessels over a torch flame or furnace by using a shaped form on a stick. This is a particularly ancient technique, actually, since some of the best examples of it come from the Hellenistic and even the Egyptian periods. That is as far back as the 16th century BCE.

In the ancient period, the vessel forms were created using animal dung, straw, clay and water mixed to make a paste, which was then applied to a glassworking rod. The forms were dried completely, and then the shape was refined into what the glassworker wanted it to be. Glass was applied by either trailing the molten glass around the core, much as lampworking is done, or the cores could be dipped into a crucible furnace that holds a 'soup' of molten glass. In some cases, the theory is that layers of frit were applied and fired. Frit is basically crushed glass, and it can be mixed with water to form a paste, which could then be applied to the core.

This photo shows some core material remaining in the vessel:

Photo by Christine Brandel

Once the glass was applied to the core, the whole thing would then be fired in the furnace until the glass was uniformly melted and cohesive. The vessel could be decorated, as so many were, with thin lines of glass wound around the vessel and then shaped using a sharp tool.

Common decorations were plain trailed lines, feathered lines, and shifted lines. As a lampworker, I can attest to the skill and steady hands required to place such thin lines around a shape in such a uniform manner, and to manipulate these lines without mangling the vessel or destroying the lines!

Feathered lines look like this:

Photo by Christine Brandel

The vessel in the back, on the far left side shows a good example of feathered lines. In the back middle vessel, and the front right vessel, the decoration is more like what is called 'festooning', ribbon-like designs with some curvature.

Once the piece was finished, the cores would be scraped out and the vessel was then ready for use. They were often used to hold kohl, for eye makeup, or for holding other oils, unguents, or small amounts of liquids.

Recently, the Corning Museum of Glass had a post on their blog about core vessels. The museum Explainers, volunteers who talk to visitors about the works in the museum, completed a workshop with hands-on experience in making the cores in the traditional manner, using traditional materials.

There is a Japanese glass artist who makes core-formed vessels. His work is evocative of the ancient vessels we see in museums today, but has a completely modern spin. Beautiful!

I hope you have enjoyed today's foray into ancient, pre-medieval period glassmaking! Below are some further references to explore on the subject, if you'd like more information.


Taylor, Mark, and Hill, David. Roman Glassmakers. Newsletter 7, January 2005. Web. 2 October 2011. <>

Kritzek, Mandy. "Dung-Core Vessel Making: Explained." Behind The Glass. Corning Museum of Glass. Web. 2 October 2011. <>

The J. Paul Getty Museum. Current Exhibitions: Molten Color. Web. 2 October 2011. <>

Nicholson, P. T. and Shaw, I. (eds.) (2000) 'Ancient Egyptian Materials and Technology' Cambridge University Press. Ch.8, 'Glass'.

Friday, August 26, 2011

Mosaic Bowls!

I promised you all a post about mosaic bowls it is!

This is what I am talking about....

Roman mosaic bowl, circa 1st c. AD
The Corning Museum of Glass

This is an example of a Roman or Hellenistic mosaic bowl. It was constructed by preparing canesof glass, long rods with designs layered in them. These canes were sliced into small pieces, revealing the layers of colored glass, and the slices were placed side by side to form the initial shape of the bowl.

Some say the bowl was formed by placing the cane slices into the bottom of a two-part mold, replacing the top of the mold, then firing to fuse the slices.

Other researchers feel that evidence supports the fusing of the cane elements into a flat disk, with the striped rim applied while the glass is hot, then slumping the disk over a convex ceramic form, thus forming the bowl.

Personally, I'm inclined to believe the latter hypothesis. Having worked with cane slices before, I find it difficult to believe that numerous slices would be placed in a mold and would stay securely while the top of the mold was put in place and fired. Those little slices of glass would be moving all over the place, unless some kind of wash or preparation was applied to stick them in place. The problem with that, in my opinion, is that whatever was used to stick them in place could contaminate the work. It seems like a whole lot of effort to go through when a simpler solution is technologically available. It's a much much simpler process to lay the cane flat on a kiln shelf, and fuse the entire thing, then slump it over something to the desired shape. This way, the ribbon edge can be hand-applied in the heat of the kiln while the disk is flat, making it much more uniform.

Here are a couple of other examples of extant bowls:
(all photos taken by me at The Corning Museum of Glass, October 2010)

Similar to the mosaic bowls are what are termed 'ribbon bowls'. They are made form long slices of cane, as opposed to the short chunks as the previous examples. The construction method is the same: sticks of glass are laid side by side, cut to length to make the desired round shape. The disk is fused and the ribbon rim is applied. The disk is then slumped over a mold to make the bowl shape. Here are some examples:

I hope this post has proved informative and interesting. Roman and Hellenistic glass is beautiful, functional, and technologically advanced, and very much worthy of scholarly attention.

Some good resources on the subject include the following:

Roman Glass in the Corning Museum of Glass:

Wednesday, August 10, 2011

The Yale Museum

I want to direct your attention to a fantastic resource on the web for ancient art, including plenty of ancient glass. It is the Yale University Art Gallery, and it is located, obviously, at Yale University in New Haven, Connecticut. I've never actually been there, although it's on my list of To-Visit Museums, but I have utilized their online resources, image gallery, and downloadable guide.

Their Ancient Glass: Guide to the Yale Collection is available here, and contains some excellent images and information about glasswork and artifacts in their collection.

I'll be back later this week with a post about mosaic bowls!

Friday, April 8, 2011

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.

Monday, March 28, 2011

Grave Goods and Rituals

I had to attend a family funeral last week, and as I attended the various services and family functions, I was reminded how the rituals involved with funeral practices in modern times have parallels in early history.

In the pre-Christian era, it was customary to place worldly goods alongside the body of the deceased as he or she was buried. This practice extends back to Egyptian pharoahs and ancient times, as well as into the Medieval period. Sending your loved one from this earthly world into the next (whatever place your belief system thought that might be) without that individual's belongings was unthinkable. A warrior needed his weapons, the deceased must have clothing and their items of personal adornment to be presentable in the next life, and everyone had to have valuables and coin to pay Charon for the trip. It's because of these types of burials that we have some of the artifacts from the earliest periods of history.

For example, look at this picture of grave goods found in a late Roman burial in Boscombe Down, Wiltshire, Wessex. Two glass vessels were found among the objects in the grave, and they are intact. Much more recently, a Roman mosaic bowl was found, not intact, but entirely restorable with all its pieces. In the Merovingian culture, burial with goods was common, and we see glass vessels placed at the feet of the deceased, sometimes with food or liquids inside. In fact, the Merovingians were notorious for rich collections of grave goods, and many of the burial sites included glass vessels. Historians are thrilled to be able to find intact glass objects in this manner. Later-period people did not have so much focus on interring goods with the deceased, and so even though glass became more common and its use more widespread over the centuries, we have far fewer intact or whole examples. Glass breaks!

Of course, in addition to vessels, people were buried with other glass objects, most commonly glass beads. As in this find, often the number and type of glass beads is stunning.

The Pagan Lady's Necklace circa 950AD
found on the Isle of Man in 1984
glass and stone beads

Most of what we know about early glass use is because of burial sites unearthed in modern times. I always find it interesting as to what was chosen to be placed with a society's dead.

As I recall the funeral I just attended, in which photographs, a rosary, some jewelry, and other items of personal significance were placed in the casket of my family member, I think about why we still do that in this day and age. These days, in my family, we don't really believe that coins are needed to pay Charon, or that my beloved uncle will use the rosary or need his wedding ring or look at the photographs, but we do it because we want to acknowledge the significance of his life. I believe that people throughout history wanted to make that acknowledgement for their dead as well, which is why we find so many interesting things among the deceased members of ancient societies. It helps us feel as though we are 'doing something' in the face of a terrible event -- and that desire is basic human nature, no matter the century.

Sunday, March 20, 2011

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.

Sunday, March 6, 2011

University links

For those of you who were not able to attend my classes at the recent University of Atlantia, here are the links to the presentations on Google Docs.

This is the link to 'Early Medieval Glass Vessels'.

And this is where you will find 'Standing On The Sea of Glass: Late Medieval Glass Vessels'.

For a look at the bibliography and references list, go here.