Large Fragment of a 2nd Century Floor Mosaic from Antioch
This fragment of an ancient floor mosaic was excavated in 1938 as part of a large archaeological excavation in Antioch, on the Orontes River in southern Turkey. Found in the dining room of a luxurious ancient home known as the House of Iphigenia, the mosaic was gifted to Cornell University in the late 1930s by Princeton University, which was a leading American institution on the site's international excavation committee. The mosaic was probably gifted as the result of a Cornell professor's involvement with the excavation and its catalog.
After its arrival at Cornell University over 80 years ago, the mosaic was never uncrated, and the heavy crate and its contents were eventually moved to a university warehouse, where it remained for several years. A recent effort to install the mosaic in the newly-built Klarman Hall required a methodical unpacking, assessment, repair and stabilization, consolidation, and cleaning of both the tesserae (tiles) and the backing cement.
The crated mosaic in warehouse storage
When it was discovered that the mosaic was broken, the crate was opened from the back, to prepare the cement backing to be repaired. The straw that was used as packing material in the 1930s is visible in this photo.
During excavation, the tiles had been moved to a new cement ground, and probably during one of the crate's moves, that cement ground had broken. The broken sections were repaired from the back of the cement slab, by injecting adhesive into the break lines while the mosaic slab was still supported by its crate. Then the back of the crate was closed, the front was opened, and the repair was repeated from the front of the mosaic.
The stabilized mosaic from the front, still in its crate
Because the repaired slab is twelve feet long and weighs over 800 lbs, but is only two inches thick, the danger of it snapping during travel to the installation site was controlled by mounting it onto a level armature made of steel and wood, so it could ride flat. Once safely at the installation site, the mosaic was cleaned and the losses were filled and colored.
The mosaic on its new armature is loaded onto a truck
Frequently, the tiles of floor mosaics that have been underground for centuries need to be moved to new slabs at their excavation sites. Over many years, ground water can leach the lime out of the original mortar that makes up a mosaic's backing, and leave behind an unstable bed of sand on which the tiles loosely lie.
To move the tiles to a new slab during excavation, a piece of cloth is coated on one side with adhesive, then pressed onto the surface of the loose tiles. Once the adhesive dries, the tiles can be lifted out of their mortar in place on the backing cloth, so they retain their design relative to each other. When a new slab of wet cement has been prepared, the cloth-backed tiles are pressed into it (fabric side up), and the cement is left to cure. Finally, the cloth is wet from the top to reactivate the glue, and then peeled off the surface of the mosaic, leaving the tiles behind in the new slab.
Over a period of two weeks, the treatments were executed in a bustling area in the atrium of a student cafe in the heart of the campus.
At the same time, a site was prepared for its installation. To prevent damage to the mosaic, it was mounted vertically and inset into a wall, rather than installed as a floor. Cornell architects and carpenters created a recess in a large wall (under a multi-panel digital screen that broadcasts campus news and events), and tied a strong steel ledge into the building's framework.
The prepared installation site
A dramatic cleaning in progress
This process was used to move the 2nd century tiles of this mosaic to a new cement slab in 1938. But the glue remnants were never removed from the surface of the tiles, so there was still a thick layer of collagen glue intact on the mosaic. Over 80 years, the glue had discolored, hardened, and attracted dust and other debris, so the colors and design of the original mosaic were obscured.
Detail of limestone tesserae before cleaning
Detail of mosaic surface before cleaning
Detail of limestone tesserae after cleaning
Detail of mosaic surface after cleaning
A small fragment of the cloth used to move the mosaic during excavation, found stuck to the surface of the tiles during cleaning
When cleaning an object, creating a cleaning solution that is effective and safe depends upon identifying both the layer that needs to be cleaned away, and also the material that was used to make the underlying artwork. Selecting chemicals that solubilize the foreign material without damaging the underlying object is critical to a surface cleaning.
These mosaic tiles are are all natural limestone. Primarily composed of calcium carbonate, limestone exists in a wide variety of colors, which come from other minerals and elements having mixed with the calcium. The overlaid glue was an animal collagen protein, and traces of wax were also found on the surface. Acidic solutions can etch and erode limestone, so they need to be avoided. But alcohol both crystallizes and solubilizes collagen, and does not chemically react with calcium carbonate. So a solution of water, a mild paste surfactant, isopropyl alcohol, and mineral spirits were used to clean the mosaic, with the help of nylon brushes, and cotton swabs and pads. In some places, the solution was applied in a gel form to poultice and loosen particularly thick areas of surface build-up.
The cleaning was quite successful, uncovering bright natural stone colors and revealing a pattern that was part of a larger design's border.
Before treatment
After treatment
After the mosaic was clean and dry, filling began on the lost sections. Gypsum plaster was used to build up and fill the lost sections of tile and mortar. The goal of restoring ancient mosaics usually stops short of filling lost designs with new tiles or tricking the eye with painted versions of rebuilt patterns. Rather, archaeological material requires a sensitivity and restraint that aims to neatly stabilize original material, and make fills visually recede but not disappear. With that in mind, the new fills were colored to match the cement ground, but the missing tiles were neither replaced nor drawn in.
Section of gypsum plaster fills
Fills colored to visually recede and match the cement ground
A large area of tiles was missing from the center of the mosaic at the time of excavation, so a sizable patch of the 1930s cement background still shows, where there are no tiles on the surface. The pattern was lightly sketched over the exposed cement on that section with reversible color pencils, but the design restoration was kept quite subtle, so the addition is only apparent when a viewer is very close to the mosaic.
Once the entire surface was cleaned and filled, it was rolled on lifts directly under the prepared section of wall, then tipped into place on the ledge that had been built and inset into the wall to support it. Padded steel brackets hold it in place.
A 1/2" thick layer of glass was installed flush with the wall by a glass shop, to protect the surface of the mosaic from food, hands, and accidental impact in a busy environment where people are frequently in close proximity to the installation.
A subtle design recreation was sketched on a large area of tile loss
For more reading about this project:
http://news.cornell.edu/stories/2018/01/second-century-mosaic-installed-klarman-hall-atrium
http://cornellsun.com/2018/02/04/second-century-mosaic-is-newest-addition-to-klarman-hall/
Movers helped tip the slab in place on a ledge that had been inset into the wall.
After thick glass covered the mosaic, Cornell Carpenters framed the edges of the installation site.
The completed restoration and installation