Conservation Process for the Caeretan Hydria

Step 1: Laying out Pieces

The first step in understanding how to conserve the Caeretan Hydria was understanding how much of the vessel we had. During this proccess, we laid out the Hydria on a table in a 3D perspective coming out from the top of the vessel. We discovered that we had the majority of Hydria, including the entierty of the base and belly. Sadly, the fracture point of the vessel is in the middle of the figural scene. Thus, the majority of the animal's head was lost.

Step 2: Photogrammetry, RTI, and 3D Modeling

Before the Cleaning and Conservation Processes began, we decided to document the larger fragments in condition photos (found in Browse Items and Interactive Hydria) and in 3D models. Reflectance Transformation Imaging (RTI), which synthesizes a series of photos with a fixed subject under different lighting conditions, was used to observe the surface damage. As seen in the video, the contrast was maximized to visualize the scratches on the surface. These photos and 3D models provide a detailed and dynamic conservation record. This record can be used to show where the vessel started, through the process of cleaning and assembling to the final restored hydria. 

3D Model of Completed Vessel:

Sketchfab Link: https://skfb.ly/oRp8F

Step 3: Research

Our Caeretan Hydria is one of about 40 vessels from Caere around 530 - 500 BCE. Because of this small sample size, we wanted to research the figural design in an attempt to figure out who the painter was. At the beginning of the conservation process, we believed the figural design was a comical scene depicting a hunter trying to kill a donkey. After much debate and close study of other figural designs, this hypothesis was proved wrong. Now we believe the design is a depiction of Herakles' Third Labour: The Capturing of the Ceryneia Hind. (Another example of this scene can be seen in the third photo above, which shows the central scene on a mastos cup in Munich. Our hydria's design is shown in the drawing.)

Step 3: Ultraviolet Fluorescence

UV fluorescence was used to identify the substances used in prior conservation efforts. These substances include adhesives, like shellac, and antiquated consolidants. UV fluorescence forces specific substances to glow according to their chemical makeup, allowing for easier identification. For example, one of the two adhesives that were used on the break-lines in the fragments is Polyvinyl acetate (PVA). The chemical makeup of PVA is soluble in acetone. The identification of substances helps conservationists know what chemicals (and how harsh the chemicals have to be) to clean the surface of the vessel. 

Step 4: Cleaning

At the beginning of the cleaning process, pure water at room temperature was used for a test to understand how pieces might react. This successfully removed dirt from the inside of the piece, but salts began to rise out of the test piece. On the surface of the fragment, water had a limited effect on removing the dirt. Next, heated water was tested; it was ineffective.

On the surface of the vessel, a more aggressive treatment was needed, a mix of heated water and ethanol solution was used for spot treatment. In addition to the new solution of water and ethanol, the method of poulticing was used. Poulticing is using fibrous cellulose cotton material combined with a heated solvent to create a thin layer of solution that remains on the vessel for an extended period of time. This was used to remove some salts and to reactivate the plasticity and solubility of the aged varnishes on the surface for easier removal. 

For the adhesive used on the vessel at break-lines, PVA is soluble in acetone. Thus, a combination of acetone, ethanol, and mechanical removal with a scalpel was used to clean the break line of all the fragments.

Step 5: Reconstruction of Vessel

To prepare the adhesive, 50 grams of Paraloid B-72 was dissolved in 90 mL of acetone (33% concentration of B-72). To dissolve the B-72, it was wrapped in cheesecloth and suspended over the rim of a glass jar so that the fabric barely touched the surface of the acetone. The jar was sealed and the solution dissolved for 12 hours.

In the timelapse above, the intern for this project, Lylah, is using small nozzled tubes to spread the adhesive along the fragment edges when gluing the pieces together. Having numbered the fragments, Lylah reassembled the hydria from the base to the neck. The entire reconstruction process took two days to complete. During the gluing process, any excess adhesive was removed using a cotton swab and acetone.

The adhesive used for the reconstruction is reversible meaning the object can be disassembled if necessary for updated conservation.

Step 6: Completed Vessel

The following images are of the completely restored and reconstructed Caeretan hydria. When working with the damaged figural scene sherds, Lylah decided against reconstructing the doe’s face as the sherds were too fragile and numerous to form an accurate depiction.

Photogrammetry and 3D Modeling of Fully Restored Vessel

What comes next?

Sadly, the conservation process of the Caeretan Hydria was too labor-intensive and delicate to finish in one semester. As the solvent strength necessary to completely poultice the vessel is quite strong, without the assurance that it will be completely successful, the Collaboratory decided to pause further cleaning for the object's safety. Lylah used a reversable adhesive for reconstruction to allow further conservation at a later date. 

In the future, the Collaboratory hopes to examine and analyze specific samples taken from the hydria, including a fiber (hair-like) deposit and dirt samples. Should substantive information result from these examinations, they will be documented here.

Future Conservation Steps:

These are some of the procedures not performed during the conservation process due to the vessel's current condition. They could, however, be completed at a late date should the full cleaning of the hydria be completed.

Desalination:

Desalination is a process where salts are extracted from the terracotta. The vessel is soaked in water for an extended period to pull the water-soluble salts out of the terracotta. The vessel must be left in the water long enough for all the salts to exit the surface completely, lest the object dries with a salt deposit on the surface and possibly cracks. To perform desalination the previous surface varnish and any other substances on the vessel must be removed for the salts to fully be extracted.

Consolidation:

Consolidation is the sealing of the vessel's surface with a varnish. A consolidant protects the ancient terracotta from exposure to dirt or water and forestalls the surface paint of the ornamentation from degrading. This process should only be completed when the vessel is fully cleaned or else it prevents most future repairs. Consolidation can be semi-permanent depending on the substance used and can degrade over time if not applied correctly.

Gaps:

Although the larger fragments of the vessel can be easily glued together, some pieces are too small to be accurately placed, or sherds are missing. These gaps are often filled with plaster, either to create a smooth surface that reflects the original appearance of the vessel or to stabilize it. Should the full cleaning of the hydria be completed, the wax-molding method used in combination with colored plaster to fill the small gaps would be recommended. In this case, warmed wax would be pressed against the inside of the vessel in a fully intact area (at the same height of the area with the gap) to get an accurate mold. Then this wax mold would be moved and taped on the inside of where the gap is located and plaster would then be used to fill it in.

However, if this step is ever carried out, the fragmented area of the animal’s head in the hydria’s figural scene should remain free of any restoration, as the head’s original appearance is unknown. Notwithstanding that the original figural depiction is unknown, I would still recommend not filling this area in. I think that leaving certain gaps unfilled in a conserved vessel enables viewers to better understand the journey of how the object came to its current destination. For the UMD hydria, the fragmentation of the animal’s head provides clues about how the vessel broke and what caused the splintering of the sherds.