Ways to preserve mosaics

Most archaeological sites we can visit nowadays date from Roman times. In the 2nd century AD, Rome reached its apogee under the reign of the five "good" emperors: Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius. They constructed monumental public buildings, and the houses of the Roman citizens were also lavishly decorated, often with frescoed walls and telling mosaic floors. 

The best-known examples are the houses and villas in and around Pompeii and Herculaneum. Still, many sites in Greece (like Pella and Vergina) and Turkey (like Ephesos and Sagalassos) also treasure such striking walls and floors. 

Some mosaic floors are left in situ where they rightfully belong, in which case they need to be protected from the elements. Shelters for this purpose are then constructed. However, even these shelters need to be maintained, which is not always the case. 

Another way of protection is to cover the mosaics with a tarp held in place with a layer of gravel. This procedure requires less maintenance as only the edges have to be checked. Many curious visitors will be tempted to push the tarp and the gravel aside to look underneath. The mosaic floors are "eaten" away from the fringes without careful and repeated care. 

Anyway, this manner of preservation is a favorite among archaeologists because it requires little or no maintenance. However, plants' roots may damage and displace the tiny tesserae. 

The most appropriate way to save a mosaic is to remove it from its spot and entrust it to the care of a museum where it hopefully will be on display. 

Such removal is very time-consuming and expensive as the top layer of the tesserae has to be detached from the existing floor in one piece. For this purpose, archaeologists use a large wooden cylinder around which the mosaic is rolled face down. A facing of two layers of fabric and an adhesive are applied to prevent losing tesserae or damaging the surface during this tricky operation. The entire mosaic floor can then be moved to its new location using a panel of aluminum honeycomb and resin following the most recent techniques. 

When strolling through a museum, the visitor is seldom aware of the effort and delicate work involved in displaying the mosaics for us to enjoy. We better take a closer look next time we visit a museum!