Week Three

This week the project worked on mosaic consolidation! I was lucky enough to be able to help out and experience on-site conservation firsthand. The mosaics on site are likely from Late Antiquity and are absolutely brilliant. They were uncovered during the first and second seasons of excavation, and the majority have held up surprisingly well given the disruption the site has faced.

A conservator is coming to assess the state of the mosaics later this season, but for now measures had to be taken to ensure that the mosaics would remain in good condition while in situ. This did not come without a series of challenges; for one, there is not a trained conservator on site, which limits the technicality that the consolidation measures can take. Another factor that must be considered is the reversibility of the process. The measures taken will need to be easily reversed by a conservator if another method of conservation is deemed necessary later in the project. Yet another factor is the availability of materials in rural Portugal. This greatly influences the types of conservation that can be attempted. After all these factors were taken into consideration, Dr. Sanchita Balachandran of the Johns Hopkins Archaeological Museum advised the project that a Gum Arabic solution would be most effective in holding the mosaics together in sections where tesserae had come apart or been lost entirely and least invasive overall. Gum Arabic is water soluble and would easily be able to be removed by a conservator. Additionally, cotton gauze could be applied around the edges to ensure that the tesserae would remain intact in the most sensitive areas.

The process for consolidating mosaics using Gum Arabic solution in situ was relatively simple, yet effective. It began with pure Gum Arabic, blocks of tree sap, that were crushed with a hammer into smaller bits. The Gum Arabic was then weighed on a scale. Once its weight in grams was recorded, the number was multiplied by four to determine how many grams of water would be needed to create a 1:4 solution of Gum Arabic to water. The two ingredients were then combined in a water bottle, shaken thoroughly, and dissolved in the sun. After sitting in the sun for about half an hour, the solution was mixed entirely and ready for application.

Pure Gum Arabic

Crushed Gum Arabic being weighed

Weighing the water for the solution

Dissolving the solution in the sun

Once the solution was prepared it was applied liberally to any cracks in the mosaic using a paintbrush. This step took us the better part of the morning before break as we checked repeatedly to make sure that each area where the mosaic was not fully mortared was covered. After the solution was applied directly to any cracks in the mosaic, the edges and holes needed to be addressed. The tesserae at the edge and in areas where large groups of tesserae had fallen away were most in danger of becoming separated from the rest of the mosaic and needed attention beyond Gum Arabic. The solution to this problem was to cut strips of cotton gauze and apply them to the edges using the solution. This gave the mosaic additional support and was equally reversible.

Solution and the paintbrush used for application

Cotton gauze strips

Me in the process of applying gauze to the edge of the mosaic using solution

The mosaics on site are now consolidated and will soon be packed away for the season. It seems that in situ consolidation is a series of difficult decisions to determine whether preservation efforts will ultimately help or hurt the object being consolidated. The site’s mosaics vary from excellent to poor preservation, leading to a variety of conservation techniques being applied. As we decided where to put the Gum Arabic on mosaics that were in better condition, the mentality of “less is more” was ever-present. If a mosaic was able to survive for nearly two millennia, it could potentially be less helpful to try and fix something that was not broken. Another challenge to consolidation was the presence of plaster near cracks in the mosaic. The goal of the consolidation effort was to only cover small parts of the mosaic and avoid other materials, such as plaster, entirely, to ensure their own preservation. While this made some parts of the consolidation effort difficult, it ultimately was preferable to keep all parts of the site in their best possible condition.

Along with mosaic consolidation we finished removing the sector I have been working in for the past two weeks. Excavation is moving quicker and quicker as the season progresses. Our dig has two sessions, and while I am staying for both, Session One is drawing to close on Sunday and many crew members will be leaving. I am excited to meet the new crew but will definitely miss the people who have made this session so great. Stay tuned next week for more news from Santa Susana!