Jacques Neguer discusses the conservation of the Lod Mosaic

Conservators Jacques Neguer and Ghaleb Abu Diab of the Israel Antiquities Authority are visiting from Israel to oversee the conservation and installation of the Lod Mosaic at the Legion of Honor. The mosaic was discovered below the streets of the city of Lod in Israel and arrived to the U.S. in seven panels. This mosaic floor is the centerpiece of the exhibition Marvelous Menagerie: A Roman Mosaic from Lod, Israel, which opens this Saturday, April 23 at the Legion of Honor.

FAM acting head objects conservator Lesley Bone sat down with her two colleagues to discuss the discovery of the mosaic and the conservation treatments they conducted. It is a fascinating conversation that reveals the behind-the-scenes science that goes into an object before it is placed on view and provides a rare glimpse into the way conservators think and talk about works of art.

Jacques Negeur and Lesley Bone

Lesley Bone: When you first went to work on the site, did you know that there would be mosaic panels buried below?

Jacques Neguer: Seven years before in a nearby area where housing was being constructed two beautiful mosaics were observed, and in the profile of a road cutting adjacent to this site there was also evidence of a mosaic profile so we thought that there would be mosaics. In Lod you cannot excavate where you want but in this case the authorities wanted to change the main entrance to the city of Lod so the supervisors called in the archaeologists.

LB: I observed in your videos that the mosaics were cleaned three times. First when they were discovered before they were covered up again for 13 years, then when they were lifted, and finally after the structural support was added. Were these cleaning processes different?

JN: The first time we cleaned the mosaic of dirt using brushes, then we used poultices [made of Sepiolite/EDTA and ammonium bicarbonate] to remove surface of salts (which can cover the surface with a white film obscuring the color and/or image) so as to be able to take good documentary pictures of the mosaics. This phase of the project was mainly about getting as much information as possible from the mosaics so that we could use this for funding of the lifting and the constriction of the Museum.

Thirteen years later when the mosaics were uncovered again for lifting, the surface was very easy to clean because the surface had been protected by the geo textile and sand. Specific areas were then cleaned more thoroughly which included mechanical removal of encrustations using such tools as scalpels. It was necessary to do this because the whole top surface of the mosaic was going to be covered with glued fabric layers before removing it from the ground. It was important that the fabric was well adhered to the tesserae [the individual tiles, usually square, cut from limestone or glass that make up the Lod mosaic] otherwise when the mosaic was rolled on a big drum the tesserae would become detached and the project would have been a disaster.

The final cleaning of the surface took place once we had mounted the mosaics on aluminum support. It was only then that the mosaic was once again face up right and we had to remove the fabric and glue with hot water to reveal the top surface of the mosaics.

Lod Mosaic - fish detail

LB: When you uncovered the mosaic after thirteen years of burial under layers of stone, sand and geo textile you found it in very good condition save for some biological growth on the northern corner. Did this cause staining of the stone?

JB: We are not sure what caused this growth. We think it might even have come from the textile. Even though it was green in color, it did not stain the stone, so there was no problem. The sand after the geotextile barrier repressed the microbiology overall.

LB: What adhesive did you use to glue the back of the tesserae to the aluminum support system?

JN and Ghaleb Abu Diab: First we put a very thin layer of lime plaster, very similar material that was originally used in the mosaics. Then we used an epoxy called Araldite, which we mixed with a filler material called perlite. This mixture allowed us to place a thick, even, smooth layer onto the back surface without it seeping out of control and getting onto the surface of the tesserae.

LB: I noticed when you lifted it you used two techniques, one was rolling and one was like a whole sandwich section.

JN: This depends on the mortar. If a lot of mortar detaches with the mosaic, the rolling is sometimes very difficult because you can have very strong sections and it interrupts the roll. To roll very long pieces is also dangerous because the mortar is very heavy and sometimes you cannot stop the movement (of the roll) and it can detach only the fabric, without the mosaic.

Lod Mosaic - design detail

LB: What are the tesserae made of?

JN: The mosaics that have come to San Francisco are mainly made of different colored limestone. Although, if you look carefully at the peacock feathers, you will notice that the tesserae in those are made from glass. In a square meter of mosaic there are 12,000 tesserae.

LB: How many craftsmen do you think it took to make the mosaic we have here?

GAD and JN: We calculate that it took three to five people–maybe three craftsmen and two helpers–three years to make this mosaic. Each tessera was individually placed into the surface of the plaster and we think it would have taken a day to make one bird.

LB: Will you be using Google earth to get it back in exactly the same place it was found once the museum was constructed?

JN: Yes the GPS points.

LB: What impressed you most about the mosaics?

JN: This mosaic was like a textbook example. I had studied the materials and theory of mosaic floor construction and everything that is written about mosaics, about how to build mosaics in the classical way is here. They have followed every step, like guiding lines with a sharp instrument and red pigment under the whole composition, drawings with the sharp instrument, and sinopia under-painting under the fishes section. You have everything here. It is amazing.

The Israel Antiquities Authority has created a website detailing the conservation process.

The mosaic's (at times perilous) journey from the Metropolitan Museum of Art in New York to the Legion of Honor in San Francisco is detailed in last Friday's New York Times.

Marvelous Menagerie: A Roman Mosaic from Lod, Israel opens this Saturday, April 23 and will will be on view at the Legion of Honor  through July 24, 2011.