Graduate students are here from the Eskenazi Museum of Art at Indiana University to create photogrammetric 3D models of Egyptian objects in our collection. Their project aims to eventually create a common portal so that other museums can also contribute to the collection of high-resolution 3D models. While they are mostly modeling the objects on display in the galleries, their project also provided a good opportunity for us to bring out some of our less-seen works so far kept in storage. Conservation was tasked with examining, documenting, and treating the 11 objects in storage, with the goal of cleaning to improve legibility and stabilizing as necessary for handling.
Most of these objects had never been thoroughly examined since they entered the Museum’s collection in the 1930s. After almost a century of sitting on storage shelves, they had accumulated so much grime that even the white stones looked black. Most of the pieces were made of limestone, a carbonate sedimentary rock that can often be powdery and very porous. The porosity results in dirt being drawn into the stone, rather than resting on the surface, which can make it trickier to clean. These pieces had also been coated or consolidated at some point in their history, likely to prevent powdering. The coatings seemed to have picked up and held onto significantly more black grime, rendering the surfaces patchy, illegible, and difficult to clean by traditional methods. Luckily, the Brooklyn Museum has a new Compact Phoenix laser system, which was able to very effectively remove the black grime.
The term “laser” is actually an acronym for Light Amplification by Stimulated Emission of Radiation. Essentially, a laser is a device that emits a very intense, directional form of light that can deliver energy to a surface. Materials at the surface of an object will either absorb or reflect the energy. In conservation, the most commonly used laser systems emit short pulses of infrared light, typically at a wavelength of 1064 nm. At this wavelength, most types of dirt will absorb the energy while the surface of the artwork will often reflect it harmlessly, allowing conservators to remove unwanted dirt layers without affecting the original material. The light energy absorbed by the dirt is immediately converted to heat energy, generating forces strong enough to break apart and expel the dirt particles away from the surface. This process is called ablation. When used correctly, laser cleaning can be gentle and controllable as it does not require touching the surface of the object. It can also be remarkably efficient and effective, drastically cutting down on treatment time compared to conventional methods.
For the rest of the limestone pieces in this project, laser cleaning resulted in a literal difference of black and white!