Medieval biconical bottle

A lot of objects come into the conservation lab because their previous repairs need to be redone. Sometimes the old adhesive fails and the object falls apart in our hands. But often the old repairs need to be redone more for aesthetic reasons such as when the resin used for joining fragments or filling losses has yellowed, which was the case with this biconical bottle dating to 1400-1525.

The bottle before treatment. Notice the large, yellowed fill on the flange of the bottle

In order to replace the fills the entire bottle had to be dismantled. The bottle was placed in a vapor chamber made up of two polyethylene bags, one inside the other, with small amount of methylene chloride. Methylene chloride is one of the more hazardous chemicals we use in the lab, so the bags were placed in our fume hood. We prefer to use less toxic chemicals when we can, but unfortunately methylene chloride is one of the few solvents that can help undo epoxy repairs.

The bottle disassembled

Detachable fills were made to fill the losses. In this technique a plaster intermediary fill is made and then molded. The mold is used to cast a tinted epoxy version of the fill. The size and location of the losses in this bottle made the creation of the two fills a little trickier than normal. The bottle had to be re-assembled and disassembled several times. An acrylic resin (Paraloid B-72) that easily dissolves in acetone was used to re-assemble the bottle each time.

The bottle partially assembled.

The smaller fill was made first.

Smaller loss

A piece of dental wax was softened with a hot air gun and molded over an intact area of the flange of the bottle to shape it so it would match the curvature around the loss. The dental wax was then attached over the loss to act as a backing for creating the plaster fill.

A dental wax backing was placed over the loss.

Some fragments on the opposite side of the bottle were left out to allow access to the inside. Plaster was poured into the loss from the inside. As much excess plaster as possible was scraped away with a spatula before disassembling the bottle.

Small plaster fill seen from the inside.

Once the plaster had set completely, the bottle was disassembled to remove the fill. The limited access while the bottle was still assembled meant that the plaster fill had to be shaped and sanded a little more once it was removed from the bottle. After applying a shiny acrylic coating, the plaster fill was molded with silicone. The silicone mold was then used to make a colored epoxy fill. To make the fill green the epoxy was colored with special dyes. Sometimes it takes a few tries to get the color just right. Luckily the silicone mold can be used many times making it is easy to cast another fill.

Silicone mold, plaster fill, and two epoxy castings.

The larger fill was made in a similar way, but this time plasticine was used as a backing for the plaster fill because it can be manipulated into the strong curvatures of the bottle better.  The bottle had to be re-assembled with the smaller fill in order to have enough intact surface area to create a backing for the larger fill.

Plasticine backing for larger fill

Because the fill was so large only two small fragments could be left out on the opposite side which made pouring and shaping the plaster even more of a challenge.

Two fragments were left out to allow access to the inside.

The bottle is very irregular in shape, which meant that the plaster fills, especially the large one, had to be shaped more than usual after they were removed from the bottle. An epoxy putty was added to the large fill in areas to help it match the contours of the bottle.

Large plaster fill with areas of white epoxy putty.

It took nearly 22 hours over two and a half months to complete the treatment. Now the bottle is back on display in the Early Northern European Glass window case in Glass Collection Galleries of the Museum. Check out the results for yourself!

The bottle after treatment looking directly at the large fill.

– Astrid van Giffen, assistant conservator

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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, the Netherlands, 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, NY. Since completing the ICN program, she’s 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.