3.2 Biological factors causing deterioration

Biological factors pose a significant threat to art preservation. Microorganisms, insects, and plants can cause extensive damage through chemical and physical processes. These agents break down organic materials, corrode metals, and weaken structures, leading to deterioration of various artworks.

Environmental conditions play a crucial role in biological deterioration. High humidity, poor air circulation, and temperature fluctuations create ideal conditions for harmful organisms to thrive. Understanding these factors is essential for developing effective conservation strategies to protect art from biological damage.

Biological Agents of Art Deterioration

Microorganisms and Microscopic Agents

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• Bacteria and fungi act as primary biological agents causing deterioration in artworks
  • Bacteria break down organic materials through enzymatic processes
  • Fungi produce acids that corrode metals and degrade calcareous substances
• Algae and lichens commonly affect outdoor artworks and stone surfaces
  • Algae form green or black biofilms on stone, trapping moisture
  • Lichens secrete acids that etch stone surfaces (limestone, marble)

Insects and Larger Pests

• ###wood-boring_beetles_0###, moths, and silverfish cause significant damage to various art materials
  • Beetles tunnel through wood, weakening structural integrity
  • Moths consume natural fibers in textiles (wool, silk)
  • Silverfish feed on paper, damaging books and documents
• Rodents and birds physically damage artworks through nesting, feeding, and excretion
  • Rodents gnaw on wooden frames and sculptures
  • Birds' acidic droppings corrode metal and stone surfaces

Plant-Based Deterioration Agents

• Higher plants, including mosses and vascular plants, cause deterioration through root systems and moisture retention
  • Moss growth on stone retains moisture, promoting further biological activity
  • Tree roots can crack foundations and displace stone elements in outdoor sculptures
• Spores and pollen contribute to biofilm formation on art surfaces
  • Airborne spores settle on artworks, potentially germinating in favorable conditions
  • Pollen accumulation can lead to staining and provide nutrients for other organisms

Mechanisms of Biological Degradation

Enzymatic and Chemical Processes

• Enzymatic degradation occurs when microorganisms secrete enzymes that break down organic materials in artworks
  • Cellulase enzymes degrade cellulose in paper and textiles
  • Protease enzymes break down proteins in leather and parchment
• Acid production by certain microorganisms leads to corrosion of metals and deterioration of calcareous materials
  • Sulfuric acid produced by some bacteria corrodes bronze sculptures
  • Oxalic acid secreted by lichens etches limestone surfaces
• Chemical alterations of pigments and dyes occur due to microbial activity, leading to color changes in paintings and textiles
  • Microbial reduction of iron-based pigments causes fading in ochre colors
  • Fungal melanin production can darken pigments in paintings

Physical and Structural Damage

• Insect boring, tunneling, and feeding compromises the structural integrity of artworks
  • Woodworm larvae create tunnels in wooden sculptures, weakening them
  • Carpet beetles consume natural fibers, leaving holes in textiles
• Mechanical stress from plant root growth causes cracking and fragmentation in sculptures and architectural elements
  • Ivy roots penetrate mortar joints, displacing stone blocks
  • Tree roots uplift and crack concrete pedestals of outdoor sculptures
• Biofilm formation on surfaces traps moisture and pollutants, accelerating deterioration processes
  • Algal biofilms on stone retain water, promoting freeze-thaw damage
  • Bacterial biofilms on metal create localized corrosion cells

Metabolic and Growth-Related Effects

• Metabolic processes of microorganisms result in staining and discoloration of art materials
  • Iron-oxidizing bacteria create rust-colored stains on stone
  • Fungal growth produces dark spots on paper and canvas
• Physical expansion of microbial colonies exerts pressure on porous materials
  • Fungal hyphae growth in wood cells causes structural weakening
  • Bacterial growth in stone pores leads to surface spalling

Art Material Susceptibility to Deterioration

Organic Materials

• Wood, paper, textiles, and leather are highly susceptible to biological attack due to their cellulose and protein content
  • Wood (furniture, sculptures) vulnerable to fungal decay and insect infestation
  • Paper (drawings, books) prone to mold growth and insect feeding
  • Textiles (tapestries, costumes) susceptible to moths and carpet beetles
  • Leather (book bindings, ethnographic objects) attacked by fungi and bacteria
• Natural adhesives and sizing materials increase susceptibility of composite objects
  • Animal glue in wooden joints attracts insects and promotes fungal growth
  • Starch paste in paper objects provides nutrients for microorganisms

Inorganic and Synthetic Materials

• Stone and ceramic materials are generally less susceptible to direct biological attack but affected by biofilm formation and acid production
  • Marble sculptures vulnerable to lichen growth and acid etching
  • Terracotta objects susceptible to algal staining in outdoor environments
• Metals primarily susceptible to microbially influenced corrosion, particularly in humid environments
  • Bronze statues develop patinas influenced by microbial activity
  • Iron artifacts corrode faster in presence of iron-oxidizing bacteria
• Synthetic polymers used in modern and contemporary art degraded by certain microorganisms, albeit slower than natural organic materials
  • Plasticizers in PVC sculptures can be metabolized by fungi
  • Polyurethane foams in contemporary artworks vulnerable to fungal degradation

Pigments and Composite Materials

• Pigments and dyes vary in susceptibility, with organic colorants more prone to microbial degradation than inorganic ones
  • Natural dyes (indigo, madder) in textiles fade due to microbial action
  • Some synthetic organic pigments in modern paintings biodegrade over time
• Composite materials in artworks have differential susceptibility, leading to complex deterioration patterns
  • Oil paintings on canvas show varying degradation between paint layers and support
  • Mixed media sculptures exhibit localized deterioration based on material composition
• Presence of additives, such as plasticizers or biocides, influences material susceptibility to biological deterioration
  • Biocides in modern paints may lose effectiveness over time, allowing microbial growth
  • Plasticizers leaching from polymers can support microbial growth on adjacent materials

Environmental Conditions and Biological Growth

Humidity and Moisture Factors

• High relative humidity (typically above 65%) provides moisture necessary for biological agents to thrive on artworks
  • Mold growth accelerates on paper and textiles above 65% RH
  • Wood-boring insects become more active in humid conditions (above 70% RH)
• Poor air circulation in storage or display areas leads to stagnant conditions favoring microbial and fungal growth
  • Corners and enclosed spaces in storage units prone to mold growth
  • Lack of ventilation in display cases can create microclimates supporting biodeterioration

Temperature and Light Effects

• Temperature fluctuations create microclimates conducive to biological growth, particularly combined with high humidity
  • Condensation on cold surfaces in warm rooms promotes mold growth
  • Seasonal temperature changes outdoors affect biological activity on sculptures
• Light exposure, especially in the ultraviolet range, promotes growth of photosynthetic organisms on outdoor artworks
  • Algae thrive on sunlit areas of stone fountains and sculptures
  • UV light can degrade protective coatings, making surfaces more vulnerable to biological colonization

Environmental Contaminants and Maintenance

• Presence of organic pollutants or dust serves as nutrient sources for microorganisms, encouraging growth on art surfaces
  • Airborne particles settling on paintings provide food for mold spores
  • Soil splashed onto outdoor sculptures introduces microorganisms and nutrients
• Improper handling and maintenance practices introduce biological contaminants and create favorable conditions for proliferation
  • Dirty cleaning tools spread spores between artworks
  • Overwatering indoor plants near artworks increases local humidity
• Seasonal changes in outdoor environments influence biological growth cycles, affecting conservation needs throughout the year
  • Spring pollen increases biofilm formation on outdoor sculptures
  • Autumn leaf litter accumulation promotes fungal growth on stone bases