An Unusual Charge: Conserving a Volta’s Straw Electroscope

Electroscope before treatment.

As a conservator at a glass museum, most of the conservation treatments I do are on glass, but sometimes we are faced with other, less expected materials. One of the more unusual treatments I’ve done recently was repairing the straws (dried plant stalks) of an 18th century Volta’s Straw Electroscope – an object invented by Alessandro Volta, an Italian physicist, chemist, and inventor who was fascinated by electricity; interestingly the term “volt” was named in his honor.

In the 18th and 19th centuries, curiosity and experimentation around electrical phenomenon abounded. Instruments such as this one were invented to show and later measure electrostatic attraction and repulsion. When an electrically charged object (such as a balloon that has been rubbed on your hair) is moved near the conductive brass top of the instrument, electrons move freely between the top and the dangling straws, leaving both straws with either a positive or negative charge. Because each straw has the same charge, they repel each other and physically separate. Glass plays a critical role in this instrument not only because it allows us to see this separation, but also because its insulative properties make the phenomena possible by isolating the straws from the surrounding environment.

This electroscope (2018.8.17) was acquired for the Museum’s collection in 2018. It arrived at the Museum with one of its straws broken in half and the other cracked and bent. Images of the electroscope before it was shipped to the Museum showed that both straws were still whole, although at least one was bent. The dangling straws probably moved a lot during shipping and the delicate material was not able to withstand those forces and vibrations without support.

Detail of the top after it was removed, showing the broken and bent straws.

Luckily the top was easy to remove, so access to the straws was not a problem. The instrument may have been made that way in order to replace broken straws. Replacing the straws was an option we considered, but in the end, the curator and I decided that retaining the original materials was more important.

Next, we examined the straws under the microscope to assess the damage and see how the straws were attached. The straws have metal wires running through them which are looped through two holes in a brass extension coming down from the top. The metal in the broken straw had broken into two pieces. In the bent straw, the straw was separated, but the wire was still intact and holding the two pieces of straw together.

Simple tools, in this case, a magnet, can often give us interesting information about an object. The video below shows what happened when we brought a magnet near the metal wires.

Video showing metal wires in straws reacting to a small magnet, indicating that the metal is magnetic.

The metal inside the straws is clearly magnetic and is most likely iron. The magnet also showed that the wires stop about 3 quarters of the way down the straws and do not go all the way to the tips.

The treatment itself was a challenge because the straws are so thin. A drop of glue between the two broken ends would not have enough surface area to make a stable join. Instead, a piece of thin Japanese tissue (a thin but strong paper with long fibers often used in conservation) was wrapped around each straw with an acrylic adhesive to provide additional support.

Top and straws right after treatment. The top of the electroscope was secured with two small weighed bags while the straws were raised to a level position with a piece of Plexiglas.

The uneven nature of the breaks in the straws allowed us to align the two parts of each straw and join them back into their original positions. This was not easy because the straws are so thin and light that they easily move out of position. Since they were still attached to the top of the instrument, the straws had to be supported on a raised flat surface while the top was prevented from rolling.

After the treatment was completed the electroscope was carefully packed and brought to our off-site storage area for photography. It is currently in storage where it will remain until it might one day be needed for an exhibition.

This unusual treatment highlights one of the things I love about being a conservator: every object is different and comes with its own unique challenges. As a conservator, I am constantly learning and applying my skills and knowledge in new ways. Working with a collection that is focused on a single material may make most treatments more predictable, but I still encounter unexpected challenges.

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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.

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