The bead that fell apart

As you can imagine, glass deterioration greatly affects the strength of a piece of glass, but why would a weathered glass spontaneously fall apart after years of apparent stability? We recently had that happen.

64.1.13 before it fell apart

The piece in question is a core-formed bead dating to 500-250 B.C. The bead is made of opaque white glass with trails and prunts of blue, yellow, turquoise, and red-brown glass, and was heavily weathered with a bubbly and pitted thick milky-white weathering crust with patches of dark enamel-like weathering over the entire bead. It has been in the collection since 1964 and had appeared stable. The bead was recently photographed and, to our surprise, an hour or so after it was photographed and safely replaced into a plastic bag, the bead was found broken into 3 larger fragments and numerous small bits.

64.1.13 broken into 3 larger fragments and numerous small bits

So what happened? Direct physical causes may have contributed but do not seem to be the main reason that the bead fell apart, which points towards the glass deterioration itself and environmental factors, especially temperature and relative humidity (RH), playing a role. Blackish dendritic staining (possibly manganese) on all the break edges indicates that there were cracks in the glass which had already gone most of the way through the width of the bead. It is likely that these structural weaknesses along with (slight?) climate changes and the stress from transport and handling caused the bead to break.

Detail showing blackish dendritic staining on break edge

Was this preventable? Maybe not, but to better understand what happened we need to determine if the bead could have experienced any changes in temperature and RH and how big those changes would need to be to affect the glass. In this case the main source of possible climate changes is the photography studio itself, specifically the lighting. We’re hoping that a repeat of the conditions, monitored with a data logger, will give us some insight into the effects lighting for photography has on the ambient temperature and humidity, especially on days when the lights are used for a long time.

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Astrid van Giffen is the Museum's associate conservator. In 2007, she completed the conservation training program of the Netherlands Institute for Cultural Heritage (ICN) in Amsterdam, with a specialization in glass and ceramics. Her training included internships at the Walters Art Museum in Baltimore, Md, and The Corning Museum of Glass in Corning. Since completing the ICN program, she has worked as a private conservator in Oregon and was the Samuel H. Kress Fellow in Objects Conservation at the Straus Center for Conservation and Technical Studies of the Harvard Art Museum (2008-2009). She also holds a BA (2001) in Classical Studies from Willamette University.

3 comments » Write a comment

  1. We have always used this beads image in our History of Glass educational presentations , It is shown in the” History of Beads “book by Lois Sher Dubin .Its sad to know that it is no longer a complete unit , However ancient beads where not always annealed in the most thorough way . It could have taken a few thousand years for the stress to let go completely !

  2. As a bead maker I enjoyed the up-close photos of the broken bead, but would love to see more. Bead makers can often learn a lot more from a broken bead than from a pristine one.

    If you are concerned about heat – switch to LED light sources. They produce almost no heat and are excellent for producing good color rendition.

  3. Interesting that this happened. Having worked in a photo studio, I would suggest that high localised temps are easily achieved. This may be the problem. Hard to believe that stresses exist after 2500years. I’m sure Corning will find out and tell us!

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