Conservation of a Ceramic Lekythos

Following my research last summer, I was eager to start work on an artefact NOT containing shellac adhesive. My first assigned artefact as a graduate student at Cardiff University was a Greek lekythos (olive oil vessel) from the Bristol Museum. The ceramic was terracotta, wheel-thrown and decorated in black figure style. It dated approximately to the sixth century BC. I had enjoyed working on ceramics in the past and was looking forward to treating this beauty! However, as soon as I examined the vessel, a noticed an amber-coloured adhesive on one of the vessel's failed joins. It appeared that the shellac curse had struck again!

To confirm my suspicions, a diagnostic campaign was conducted with UV, X-ray and FTIR analysis. The UV analysis showed two presentations of the adhesive: a bright orange colour (characteristic of shellac) and pale green. Research had shown that degraded shellac may present with a pale green colour under UV. A sample of the adhesive was collected, and FTIR analysis confirmed that the adhesive was shellac. X-ray analysis provided further insight into the technology and construction of the material.

UV analysis revealed the presence of adhesive, gap filler and inpainting.

FTIR analysis supported and augmented the UV results. The previous restoration materials were identified as shellac adhesive, calcium sulphate filler, and gum Arabic inpainting.

X-ray imaging revealed information on the original construction of the ceramic, as well as the thickness and locations of the fill material.

After all of the foreign materials were identified, it was time to begin treating the artefact. First, the outer surface of the vessel was cleaned with industrial methylated spirits (IMS) to remove surface dirt and inpainting. After all of the inpainting had been removed, the borders of the white calcium sulphate were more easily identified. Because the fill was so thick, a dremel was used to mechanically remove the fill. The findings of last summer's research project showed promise in swelling shellac with 1:1 IMS and acetone. A small beaker was placed in a closed container to fume the solvent. The adhesive at the neck swelled and was easily removed with a scalpel. Unfortunately, the rest of the adhesive did not respond to the solvent.

After several more tests, trials and lots of wine (outside the lab, of course), the adhesive present on the rest of the vessel was swelled in room temperature tap water. A sample of this adhesive was tested with FTIR showed a collagen-based animal glue, also supported by its solubility in water. Water was applied topically to each join to separate the fragments one at a time. The fragments were then soaked in warm water and cleaned to remove remaining fill and adhesive. They looked so nice and clean!

Finally, it was time to reconstruct the vessel! Paraloid B-72 was used to rejoin the fragments. Several tests were done to match a pigmented gypsum to the ceramic body as the fill material. A large batch of the pigmented mixture was prepared to ensure an even colour on the separate fills. Unfortunately, the large gap on the shoulder of the vessel proved difficult to fill due to the location and narrow neck. A two-step approach was adopted, and the vertical gap was filled first. After it partially dried, the horizontal gap was filled. Even though the same mixture was used, the colours were slightly different. The fill had to be worked down 2 mm below the surface and a final, thin layer of gypsum was applied. The gap fills were worked down and shaped with needle files and different grades of micromesh. IMS was used to give a final clean to the outside of the vessel.

This 3D laser scan, showing the reconstructed vessel and gap fill, were done courtesy of the Newport Ship Project with the assistance of curator Toby Jones.

Now that the vessel is clean and back in one piece, it's on its happy little way back to the Bristol Museum!

Until next time! K

#conservation #FTIR #shellac #archaeology #Greekart