Filling losses with Paraloid B-72

Last week chief conservator, Stephen Koob, and I were in Ottawa at the Canadian Conservation Institute’s “Adhesives and Consolidants for Conservation: Research and Applications” Symposium.

We went to present a new technique for filling losses in glass which was developed at the Corning Museum of Glass. For this blog I thought I’d tell you about one of the objects I recently used this technique on. This Islamic beaker is interesting for other reasons as well. During the initial examination I noticed glue on break edges for which I didn’t have any joining fragments. This lead to the discovery of a box of loose fragments in our storage area labeled with the same accession number as the beaker. Some of the fragments in the box definitely belonged to the beaker, but others clearly did not. Although no previous treatment records were found, the object had certainly been treated in the museum in the past. These extra fragments were probably used as fill material for the losses in an even earlier treatment that occurred before the beaker came into the museum’s collection.

The object in question is an Islamic beaker dating to 900-1199 A.D. It came into the lab because the old repair partially failed during handling. The beaker was broken into five sections of multiple fragments and two individual fragments and had about 15 to 20% of the body missing. Much of the severely weathered surface of this beaker has already been lost, leaving the remaining glass very pitted and much thinner than it originally was. Surface loss and pitting also occurred along the break edges causing the fragments to not join well. Missing pieces caused some fragments to be almost “floating” because they barely touched any adjoining fragments. Too much pressure was put on these fragile joins during routine handling, causing them to fail.

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The fragments and break edges were cleaned and re-assembled using Paraloid B-72 adhesive, including many of the fragments found later. Next the larger losses were filled. This was done by casting films of B-72 in silicone molds. The film was then “textured” by allowing lots of tiny bubbles to form by placing the film in the oven on a smooth surface. The result was very complementary to the weathered surface of the beaker. The B-72 film was placed over the loss in the object, and the shape of the loss was traced onto the film and cut out with scissors. Finally the fills were put in place and glued onto the glass with a small amount of acetone on a soft brush.

The paper we presented at the conference has more details about the technique of casting B-72 for fills in glass. It will be published online at the CCI website later this year.