By Kate Berlewen
This beautiful Roman glass bottle was excavated from an unknown site in Egypt by Flinders Petrie, or by one of the highly skilled and knowledgeable local men who worked on the dig sites he controlled, and is held in the Petrie Museum of Egyptian Archaeology collection. The bottle was treated in the Institute of Archaeology conservation lab at least once before in 1975, before returning to us for retreatment in 2019.
Due to the lack of information about the excavation site and any contextual dating information, the bottle can only be roughly dated to somewhere between 100CE and 650CE (Davison, 2003, p19; Rossi, 2010, p406). The colouring of the glass was likely to be caused by small and deliberately added amounts of metal oxides such as copper oxide, or a combination of iron and magnesium oxides, both of which can cause a green colour when added during the melting process (Davison, 2003, p7).
When I received the bottle for treatment it was in 35 fragments. All the pieces had adhesive left on their edges from the previous conservation treatment, and some were still adhered to each other by the rapidly failing remnants of the old adhesive and strips of pressure sensitive adhesive tape. The adhesive was identified as HMG (cellulose nitrate) in the 1975 report, and I was able to confirm this through observation in a UV light source and solubility testing.
The first step in my treatment after initial examinations was to carefully remove all traces of this old adhesive without any unnecessary cleaning of the excavation dirt on the surface of the glass. Luckily the glass surface was relatively stable and, although fragile, did not require consolidation prior to handling. After the fragments were free of cellulose nitrate, the fragments were reconstructed into as complete a form as possible using Paraloid B-72 (ethyl methacrylate co-polymer) in acetone, applied with an extremely small sable brush.
In total all but ten fragments were reassembled, and these un-locatable fragments are most likely from the large area of the bottle that is lost. These have been repackaged and included with the reassembled bottle in clearly labelled packaging. The jigsaw puzzle of reconstruction took many, many days, and at least four of my fellow students in the lab came to see if they could re-locate any I had missed. In fact, my eternal gratitude is owed to Reed Hudson who located a key fragment which allowed me to place a further three more!
Due to the vulnerability of the jagged edges of the reconstructed bottle and the thickness of the glass being less than a millimetre in some areas, I decided to attempt at least one supporting Japanese tissue paper fill. After this first support was placed, it was clear that the technique was highly suitable for supporting the fragments and the most vulnerable joins, and in total I created four support fills in this way.
The Japanese tissue was impregnated with Paraloid B-72 in acetone after being tinted with watercolour pigments to match the colour and markings on the glass. The tissue was tinted in this way because it was likely there would be some disparity between the textures and reflectiveness of the glass and the tissue, and so blending the colour would help this be less distracting to the viewer and make the overall form of the bottle more legible. I found that layering the tissue paper to four pieces thick gave suitable stability, and tearing the edges rather than cutting achieved better blending of the edges where they met the glass. Drying on a curved piece of silicon release paper also gave both shine and curve to the tissue, which could be exploited when adhering the fills to the curve of the glass.
It was important that the supportive fills had a translucency similar to the glass but with maximum support. Four layers of tissue achieved this, as demonstrated by the handle of this paintbrush held behind the fill and original glass.
I was inspired to try this technique by a previous blog from the UCL lab in 2015, describing a treatment for another archaeological glass bottle also from the Petrie Museum of Egyptian Archaeology which is linked below (Williams, 2015). The bottle from the 2015 treatment was a greater state of deterioration than the bottle I treated, but the use of Japanese tissue as a supportive, strong, but translucent fill material still worked well. I hope you agree!
Many thanks to UCL Culture, Petrie Museum of Archaeology who own this object and have given their kind permission for its treatment to be shared.
Sources:
Davison, S. (Ed.) (2003). Conservation and Restoration of Glass. Oxford: Butterworth-Heinemann.
Rossi, C. (2010). ‘Science and Technology: Pharaonic’ in Alan B. Lloyd (Ed). (2010). A Companion to Ancient Egypt. Chichester: Wiley-Blackwell. p390 – 408.
Williams, E. (2015). Japanese Tissue Paper – A Glass Puzzle from Tell Fara. Available at: https://uclconservation.wordpress.com/tag/japanese-tissue-paper/
Carla Russo is a first-year MSc student from Argentina. Her background is in Economics and Finance before eventually following her call and getting a degree in Classical Archaeology. She is very interested in cultural heritage and archaeological material, which led to her pursue of the MSc degree in Conservation for Archaeology and Museums at UCL. (Text by Carla Russo)
Figure 1. Copper-alloy armour fragments found in Suffolk via metal detector (before conservation treatment).
Figure 2. Copper-alloy armour fragments found in Suffolk via metal detector (before conservation treatment).
Figure 3. Large copper-alloy armour fragment in original soil.
Figure 4. Initial digital documentation of large copper-alloy armour fragment in original soil.
Figure 5. Large copper-alloy armour fragment in original soil.
Figure 6. Large copper-alloy armour fragment depicting a male torso with a club after initial cleaning.
Figure 7. Copper-alloy armour fragment depicting a male head during cleaning process.
Figure 8. Copper-alloy armour fragments after conservation treatment.
Conservation Lab Chat 