M . O . S . A . I . C . S20 April 2010 Maria Bonet

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

Bath floors, Ostia Antica, 2nd c BCImage taken from karalus.free.fr

‘Dionysus on a Leopard,’ Delos, 2nd c BCImage taken from

www.ancientsculpturegallery.com

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)

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

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

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

Construction of the ‘Cinderella Mosaics,’ Cinderella Castle, Magic Kingdom, Orlando, FL. Photo © Disney. Image taken from Allears.net

Detail, ‘Cinderella Mosaics,’ Cinderella Castle, Magic Kingdom, Orlando, FL. Photo © 2009 J

Spence. Image taken from Allears.net

Detail, Virgin Mary, Hagia Sophia, Istanbul, Turkey, 944 AD.

Image taken from www.mosaicartsource.com

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

Mask support is a human skull with a hinged jaw

Interior lined with leather

Tezcatlipoca, Miztec-Aztec ceremonial mask, Mexico, 14th-15th c

AD. Image © The British Museum

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

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)

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

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

On Lifting

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

Harvard University team members at Sardis,

Turkey in 1991. JAIC Online, vol. 39, no. 1.

Image taken from cool.conservation-us.org

Go ye forth and conserve!

THANK YOUMosaic Art House in

Boerum Hill, Brooklyn (c.2009).

Image from mosaicartsourc

e.com