1. M . O . S . A . I . C . S 20 April 2010 Maria Bonet

2. Early History Earliest known mosaics were created in Asia Minor and Greece Intended as sturdy floor coverings Originally constructed principally with black and white pebbles Height of Greek mosaics reached during the Hellenistic age (2nd century BC) Polychrome style popular and widely used Mosaic art introduced to Rome via Greece Monochrome or ‘Black Figure’ style popular Roman style spread throughout Roman Empire to Britain, Africa and the Middle East Wall and vault mosaics were already in use in Greece and Rome, but were principally created by Christian artists

3. Bath floors, Ostia Antica, 2nd c BC Image taken from karalus.free.fr ‘Dionysus on a Leopard,’ Delos, 2nd c BC Image taken from www.ancientsculpturegallery.com

4. Materials Support Layers of soil bedding Brick walls Wood or bone Plaster Lime Sand, pozzolana, clay, brick dust, chopped straw Tesserae Stones (marble, limestone) Glass (Smalto) Ceramic tiles Layer is known as tessellatum Tesserae from Qibbuz Kabri, south of et-Tuweiri. Image taken from Hadashot Arkheologiyot (www.hadashot-esi.org.il)

5. Technique: Floor Mosaics Common bedding layers: First: Rammed earth and un-mortared rubble Second: Opus signinum (crushed tile and lime mortar) or mortared rubble Lime-mortar bedding on which tesserae were imbedded Pictor designs the mosaic Floor area is measured and divided into grids Pavimentare lay the tesserae down. Floor grouted with mortar, then polished with abrasive stones Preparatory layers, ‘Orpheus Mosaic,’ Paphos, Cyprus. Image taken from The Conservation of the Orpheus Mosaic at Paphos, Cyprus

6. ‘Orpheus Mosaic,’ House of Orpheus, Paphos, Cyprus, 2nd c BC. Image taken from The Conservation of the Orpheus Mosaic at Paphos, Cyprus (1991)

7. Technique: Wall Mosaics Bedding layers: Brick wall Rendering / foundation bed (sand, pounded brick) Intermediary bed (lime, brick dust and chopped straw) Setting bed (lime and marble dust) Designs were sketched either directly on the brick wall or on the rendering bed Tesserae Smalto , marble, mother of pearl, jewels, gold and silver Interstices between tesserae begin to widen to increase the luminosity of the design Basilica di San Vitale, Ravenna, Italy, 6th c AD. Photograph © 2007 James Martin. Image taken from About.com: Italy Travel

8. Construction of the ‘Cinderella Mosaics,’ Cinderella Castle, Magic Kingdom, Orlando, FL. Photo © Disney. Image taken from Allears.net Detail, Virgin Mary, Hagia Sophia, Istanbul, Turkey, 944 AD. Image taken from www.mosaicartsource.com Detail, ‘Cinderella Mosaics,’ Cinderella Castle, Magic Kingdom, Orlando, FL. Photo © 2009 J Spence. Image taken from Allears.net

9. Techniques: Other Supports Support: Carved wood or bone Pine or Bursera tree (‘copal’) resins applied to support Tesserae Minerals: Turquoise, jade, malachite, pyrite, lignite Shells Polished by hand with fine sand or fine cane strands Quetzalcoatl, Miztec-Aztec ceremonial mask, Mexico, 14th-15th c AD. Image © The British Museum

11. Interior lined with leatherTezcatlipoca, Miztec-Aztec ceremonial mask, Mexico, 14th-15th c AD. Image © The British Museum

12. Deterioration Soluble salts Cause efflorescence and subflorescence, which weaken mortar and adhesives Capillary action brings moisture to the surface Incrustations form from salt migrations, pollution, site specific dirt and previous repairs Process initiated and maintained by fluctuations in temperature and moisture Stress Can be internal (crystal lattices broken as mineral ions react with a given substance) or external Cracks in bedding / mortar causes tesserae to lift, become loose or detach High volume of visitors places external stress on the surface

13. Deterioration Continues Biodeterioration Root action Bioreceptivity: Porous materials that retain moisture are more prone to biodeterioration Phototrophic bioagents (algae, lichens) encourage growth of bacteria and fungi Moisture is trapped within the material Bacteria Excrete organic and inorganic acids Can produce a protective patina Halophilic bacteria: Thrive on salt-rich environments Fungi Biofilm on weathered stone, microscopic view. Image taken from Conservation Science (2006)

14. Conservation Cleaning Water can be used to wet clean tesserae Accretions picked off with chisels, dental tools Consolidation Adhesives (Paraloid B72) Cramps inserted into bedding in order to pull together layers that have lost cohesion Grouting: Injection of mortar under the tessellatum Loose tesserae can be removed—one by one—and reattached Infilling and replacement Edging and infilling of lacunae Infill of interstices

15. More on Conservation Biocides Biostatic or biocidal Quaternary ammonium compounds are both biostatic and biocidal Organism to be fought must be properly identified before biocide is chosen Ethical issues of human toxicity and adverse effects on the stone Prevention Shelters to keep out rainwater and excessive sunlight Coatings Knowledge of the mosaics environment (weather, visitors, seismic activity, etc) Tesserae consolidation. Photograph © 2010 Enzo Aiello. Image taken from aiellomosaics.com

16. On Lifting Harvard University team members at Sardis, Turkey in 1991. JAIC Online, vol. 39, no. 1. Image taken from cool.conservation-us.org Lifting Facing: Cloth is adhered to the surface of the mosaic Rolling: The cloth is stapled to a wooden drum or roller Spillatura: Removal of backing mortar with metal awls, fraises, dental tools, etc Mosaic can then be either displayed in a museum or placed into new bedding in situ Controversy: New bedding layers can settle differently, leading to cracks Metal honeycomb backings can corrode Removal of mosaics to museums is being re-evaluated Current emphasis is on prevention and on in situ repairs

17. Go ye forth and conserve! THANK YOU Mosaic Art House in Boerum Hill, Brooklyn (c.2009). Image from mosaicartsource. com