PMG Mold Remediation

Conservation Specialties

Conservation Specialties Analysis and Imaging Preventive Care Education and Professional Development Workplace Practices About Conservation Lexicon

• Photographic Material

Group

• Photographic Materials Group

Section

• Deterioration Issues
• Emergency Preparedness and Recovery
• Tools, Equipment, Materials, and Supplies
• Treatment Techniques and Procedures

Page Information
Date initiated	September 2009
Contributors	Chloé Lucas (Page Compiler), Cecilia Salgado, Susana Hoyos, Vanessa Castillo, Luisa Casella, Amanda Maloney, Stephanie Watkins

What is mold?

Life cycle of a mold from the Aspergillus genus

Several types of microorganisms can grow on photographic materials, the most common ones are bacterias and mold. Mold is a common term referring to filamentous fungal species from the Fungi Kingdom.

Life cycle of mold

Mold is present everywhere in the air in the form of mold fragments and reproductive cells, called spores. Fungi are heterotrophic organisms, which means that they cannot produce their own source of carbon to grow, it has to come from their environment. As a result, mold spores need to settle on an external source of carbon, which is called substrate, to grow. In favourable conditions, the spores then germinate and grow forming cylindrical branching filaments, called hyphaes. Once mature, the fungi can produce new spores that will contaminate other substrates.

For more information about mold biology, please refer to the section 1.2 of the BPG Mold page.

External factors influencing mold growth

Each fungal species has optimal environmental conditions in which they will grow best. However, they can still grow under less favorable conditions, the growth will be slower. Favorable conditions vary from species to species.

Several factors in the environment influence mould growth:

• Water: Relative humidity in the environment around the photograph has an influence on fungal growth because it influences the moisture content of the substrate on which it grows. The ideal relative humidity for fungal growth is between 65% and 70%, but growth can easily happen at lower (55%) or higher relative humidities.
• Nutrients: Photographic materials, such as cellulose (primary support) and proteins (image binder), serve as a source of carbon for mold growth.
• Temperature: Each species has a minimum, maximum and optimal temperature for growth. The most suitable temperature is between 23.8ºC and 28.7ºC; however, some species can grow at lower (2ºC) or higher (40ºC) temperatures.
• Light: The amount of light required for mold growth depends on species.
• Oxygen: Fungi are strict aerobic microorganisms; oxygen is indispensable to their growth.

For more information about external factors influencing mold growth, please refer to section 1.6 of the BPG Mold page.

Intrinsic factors influencing mold growth

Presence of silver

The presence of silver as an image forming material has an impact on fungal growth. It was reported that low-density image areas, with lower amounts of silver, are more prone to fungal growth; and that silver can completely inhibit fungal growth. It was also noted that fungal growth on silver images can modify the localization of the silver within the binder, which accumulates on the surface of the fungal cell wall.

Characteristics of gelatin emulsions

Tanning:

Tanning of emulsion during manufacturing or processing (fixing bath containing tanning agents) modifies its water content. Tanning, usually with chrome alum or formaldehyde, results in reticulation of the gelatin peptide chains, thus preventing water molecules from linking with the chains, and lowering its water sensitivity. Consequently, a tanned gelatin emulsion will have a water content between 3% and 9%, compared to a non-tanned gelatin emulsion whose water content is between 11% and 14%. Fungi prefer their substrate to have a water content between 8% and 10%, so they are more likely to attack a non-tanned gelatin emulsion.

Observations made by various authors sometimes contradict this information. Indeed, Abrusci et al. did not notice a difference in fungal development between tanned and non-tanned samples. On the other hand, Dalev et al. showed that the more an emulsion is tanned, the slower the enzymatic hydrolysis will be, with solutilisation time of gelatin solution by protease enzymes increasing with the degree of reticulation. Similarly, Lourenco and Sampaio noticed that early silver gelatin prints were more easily deteriorated by fungi, which could be explained by a lower degree of tanning.

Amorphous and crystal phases:

The structure of gelatin consists of amorphous phase (coil) and crystal phase (triple helix). A gelatin emulsion with more crystalline areas will be more resistant to fungal attack, as the gelatin chains are organized into triple helix and less accessible to react with external molecules.

Gel and solid phases:

Gelatin is a hygroscopic colloid, whose water content depends on the environmental temperature and relative humidity. The water content of gelatin influences its physical property, and two phases can be distinguished: a solid phase, under the glass-transition temperature, and a gel phase, above the glass-transition temperature. Water in gelatin is not easily accessible to fungi when the gelatin is in a solid phase, it is more vulnerable to fungal growth when it is in a gel phase. The gelatin gel phase can be reached during thermo-hygrometric variations: when the temperature and relative humidity increase, the water content of the emulsion augments as well, and can go over the glass-transition temperature. This gel phase can also be attained when there is condensation on the surface of the emulsion.

Effects of mold on photographic materials

Damage caused by mold

Mold damage may not always be visible to the eye, the fungal colony needs to be of a certain size and extent to start being visible.

Structural damages:

• Change in mechanical strength.
• Change in porosity.
• Increased wettability.
• Pitting of surfaces.
• Friability.
• Partial or total loss of binder and/or primary support.

Aesthetic damages:

• Stains.
• Change in gloss (from surface pitting).
• Change in color.

Degradation mechanisms

During fungal growth, hyphaes adhere to their substrate and can generate micro-fissures into the constituent materials. Fungi secrete metabolic products which can react chemically with the constituent materials and fragilize them through oxidation or enzymatic hydrolysis reactions.

Oxidation of proteins

Various fungal metabolic mechanisms, such as cellular respiration, can produce reactive oxygen species (ROS), which are highly reactive chemicals formed from dioxygen (O₂).

ROS are rejected in the substrate and oxidize proteins until full denaturation of the protein, which is the breakage of the alpha helix into a non-organised coil. The breakage of the amino-acid chains increases the availability of amines and acids for reaction with water, resulting in an increased sensitivity to water of the protein.

Some amino acids present in gelatin - methionine and tyrosine - are particularly sensitive to ROS and the secretion of ROS into the gelatin substrate results in its oxidation.

Enzymatic hydrolysis

Fungal species can readily use simple sugars and amino acids to grow. In the presence of peptides or more complex sugars, such as cellulose, the fungi will need to produce enzymes specific to the materials - such as cellulase (for cellulose), protease (for proteins) or gelatinase (for gelatin) - in order to break it down and use it as a carbon source. Because simple sugars and amino acids are easier to assimilate, mould will be more likely to grow on an already broken down constituent material, from previous water or fungal damage.

Production of pigments

During growth, fungi can produce pigments, which can be located in the hyphaes, in the spores or secreted into the substrate. The production of pigments is species-dependent and is influenced by various factors such as the availability of nutrients, environmental factors or the presence of metal in the substrate. The formation of pigments can also result from the interaction between constituent materials and metabolic products.

Health and safety

Health risks associated with mold

Contact with mold can cause different types of reactions to human health:

• Allergic and hypersensitivity reactions: All mold species can induce allergic and hypersensitivity reactions as they are caused by the spores, mold fragments, biofilms and metabolic products secreted during mold growth. As the allergic and hypersensitivity reactions are caused by the presence of mold spores, fragments and biofilms, whether they are active or not, killing the mold does not eliminate the health hazard. The metabolic products are microbial volatile organic compounds (MVOCs), which are responsible for the moldy smell. Furthermore, MVOCs can be absorbed by porous substrates and be slowly released over time, the moldy smell can then indicate present or past mold growth.
• Irritant and toxic reactions: Irritant and toxic reactions (respiratory, immune or neurologic effects) are less common as they are caused by mycotoxins secreted by some mold species, usually as a response to a stressful growth environment.
• Infections: Mostly for people with severely compromised immune systems.

Sensitivity to mold varies from person to person, people with asthma or chronic conditions are more at risk. Moreover, the sensitivity increases with chronic exposure and permanent sensitization can occur over time. As a result there is no “safe” limit for mold levels, it is thus crucial to use protective equipment when working on contaminated photographs.

Protective equipment

Workspace

It is recommended to work in a space separate from non-contaminated materials and to isolate moldy materials to avoid cross-contamination.

The following workspaces are recommended for mold remediation treatments, depending on resources available, extent of contamination and size of photographs to be treated:

• Biosafety cabinet (with High Efficiency Particulate Absorbing (HEPA) filters).
• Fume hood.
• Indoor. In a space with no air exchange with the rest of the building. Air vents can be sealed with plastic sheets and tape.
• Outside. Under cover from the sun and far from building air intake.

Personal Protective equipment (PPE)

The mold exposure pathways into the human body are by inhalation, by ingestion, and by skin contact. It is necessary to protect your airways (nose and mouth), eyes and skin.

Airways protection:

• Disposable respirator, half-face respirator, full-face respirator or powered air purification respiratory systems (PAPRs).
• Particulate filters (N series), N100 (HEPA) is recommended.
• Organic vapour filters can be added to the particulate filter, when there is a mouldy smell (presence of MVOCs).
• /!\ Caution /!\ Filters have a limited lifetime, between 1 week and 1 month, depending on the model, frequency of use, air contamination and care.

Eyes protection:

• Goggles

Skin protection:

• Disposable gloves (PVC or nitrile)
• Protective clothing if there is a significant amount of mould. Disposable (high contamination) or reusable (medium or low contamination).
• Wash hands with soap and water after working on contaminated materials.

The type and extent of protection recommended varies depending on the size of the contamination. The Canadian Conservation Institute proposes a “Recommended Personal Protective Equipment” table to help determine which PPE to use, based on extent of contamination.

Should I use reusable or disposable PPE?

Reusable:

• Must not be worn outside of a contaminated area to avoid cross-contamination.
• Needs to be cleaned and disinfected after each use.
• Can be shared only when they are properly cleaned and disinfected.

Disposable:

• All disposable equipment is strictly personal and must not be shared.
• Gloves and protective clothing can be reused until they are damaged and do not fulfill their safety purpose anymore. If reused, they must be cleaned before and after every use (before removing them):
  • Gloves: with soap and water, as a regular hand washing process.
  • Protective clothing: carefully vacuumed.
• Discard in a sealed thick plastic bag in a regular garbage container. /!\ Caution /!\ Legislation may differ depending on location, consult local information sources.

Purpose of mold remediation for photographic materials

• Minimize the spread of mold within the collection

To prevent contamination of the photograph’s enclosure, surrounding photographs and storage space during use.

• Minimize detrimental health effects to users

To  lower health risks associated with the presence of mold during use.

• Minimize the effect on the collection

To prevent future growth of the mold currently contaminating the photograph, thus lowering the risk of damage.

Factors to consider

• How many objects need treatment?

Mass treatment vs. Itemized treatment. Some treatments are more appropriate for a mass/itemized treatment.

• What types of photographic materials need treatment? Are they in good, medium, poor condition?

Consider the effect of various mold remediation treatments on constituent materials. The effect of a treatment can vary depending on the condition of the photograph.

• Who uses the collection? How often?

Killing the fungi does not remove the risk of detrimental health effects for users. Photographs that are handled often may need additional preventive measures to protect users.

• How efficient is your climate control system?

Mould growth can be minimized by strict storage environment control. Photographs returning in a storage space with limited environmental control will be more at risk of future mold growth. Furthermore, mold damaged photographs are more susceptible to future mold growth because the constituent materials are already partially or completely broken down, as a result they are easier to assimilate by fungi.

• What are the short and long term effects of the treatment on health and the environment?

Consider the toxicity of the treatment to human health, the impact of the production and disposal of chemicals on the environment, and the potential retention of chemicals within porous constituent materials.

• What resources do you have access to?

Consider monetary, space and human resources needed vs. available.

Should I identify the mold species?

The effects of mold remediation techniques can differ from species to species. In most cases, the limiting factor is the treatment’s effects on photographic materials, rather than its efficiency on various mold species.

In the event of a mass mold contamination and for some types of treatments, it may be useful to identify the contaminating species. However, the identification is limited by the fact that any species identified on the surface of the photograph may have just deposited there, and may not be responsible for the contamination or visible damage. There is a risk of mis-identification of the contaminating mold species.

Mold remediation techniques

Terminology:

• Viable: mold that is able to grow (alive).
• Non-viable: mold that is unable to grow (dead or killed).

• Active mold / active growth: mold that has germinated and is growing (at any rate).
• Inactive mold / not actively growing / deactivated: mold that has stopped growing.

• Fungistatic treatment: treatment resulting in the deactivation of the mold, it is still viable.
• Fungicidal treatment: treatment resulting in the non-viability of the mold.

Thresholds of cleanliness

To approach mold remediation Eng Moore and Maitland proposed a framework dividing remediation in two thresholds of cleanliness. The first threshold goal is to minimize the spread of mold within the collection as well as the detrimental health effects to users; while the second threshold goal is to minimize the effects of mold growth on the collection.

The first threshold should be undertaken in all mold contamination situations and can be achieved with the following steps:

• Drying: to stop mold growth: most fungal filaments will become non-viable, while the spores will be deactivated but still viable and able to grow once conditions are favorable.
• Dry cleaning: to lower the overall amount of mold on the object by removing a maximum of loose spores, mold fragments and filaments from the surface of the photograph.
• Containing: to prevent mold spread and cross-contamination.
• Controlling the storage climate: to prevent future mold growth.

The first threshold is not fungicidal, but minimizes the risk of the same mold growing again and risks to human health by lowering the amount of mold present on the object. Indeed, as photographic materials are often porous (binders, paper supports), it may not be possible to remove all mold structures (viable and non-viable), embedded in the materials, without damaging the object.

In some cases, particularly when there is severe mold damage or when the environmental control is limited, the second threshold can be undertaken, and achieved with the following steps:

• Implementing threshold one.
• Killing the remaining mold: to prevent future growth of the same fungi, with a fungicidal treatment.

Implementation of the second threshold does not remove the risks to human health, because the embedded fungal structures are still present. Furthermore, fungicidal treatments are not a preventive measure. Treated objects are still susceptible to mold growth from newly deposited spores. They are also easier to contaminate than objects in good condition as the materials are already damaged.

Dry cleaning (Threshold 1)

Goal:  Minimize the spread of mold within the collection as well as the detrimental health effects to users.

Advantages:

• Not toxic for humans or the environment.
• Low budget.

Disadvantages:

• Not fungicidal.
• May not be possible to remove all the fungal fragments embedded in the materials.
• Does not remove mold-related risks to human health.

Factors to consider:

• Condition of the photograph:  for structurally weakened materials it is recommended to use a polyester screen as an interface over the object and/or as a filter on the vacuum cleaner’s nozzle.
• Suction of the vacuum: can be adjusted with miniature tips, a vacuum with adjustable suction, or by placing your hand to partially block the nozzle.

Tools:

• Personal protective equipment.
• Vacuum with HEPA filters or water trapping - to avoid releasing the mould spores into the air. Miniature tips can be added to adjust suction.
• Soft brushes - dedicated to mould remediation, do not use for other tasks to avoid cross-contamination.
• Polyester screen.
• Weights - should be easy to clean (non-porous materials), and can be separated from the object with a blotting paper if the surface is fragile.

Procedure:

• Wash your hands.
• Put your PPE on.
• Place the photograph on your working space.
• Maintain the photograph with weight(s).
• Place the vacuum tip above the photograph, approximately 10 cm away depending on the photograph’s condition and suction level.
• Delicately brush the mould toward the vacuum nozzle. Apply light pressure to avoid embedding the mould in the constituent material, particularly if it is porous.
• Methodically brush the whole surface of the photograph, even if there is no visible mould. Brush each side of the photograph twice, once vertically and the second time horizontally. Move the weight(s) to clean underneath it/them.
• Clean your tools and working space.
• Remove your PPE.
• Dispose of contaminated non-collection materials and disposable PPE.
• Wash your hands.

Fungicidal treatments (Threshold 2)

Goal: Minimize the effects of mold growth on the collection. In the context of heritage collections, killing all living spores with a sterilization treatment is not the goal as collections are not stored in a sterile environment. Fungicidal treatments aim at lowering the amount of viable fungal spores on a photograph to a level similar to the ones present in clean collection space.

Alcohols

Advantages:

• Low toxicity.
• Low budget.
• Several application methods, which can be adapted to the object.

Disadvantages:

• Detrimental effect on some photographic materials.
• Toxicity.
• Does not remove mold-related risks to human health.

Factors to consider:

• Type of alcohol: The effectiveness of different types of alcohol varies with their carbon chain length: the shorter the chain, the more effective the alcohol is. As a result, methanol (CH₄O) is the most efficient alcohol for mould remediation; however, due to methanol high toxicity, ethanol (C₂H₆O) is usually preferred.
• Alcohol-water ratio: Research has shown that alcohols used undiluted have no antifungal action and that it is necessary to use it mixed with water to allow its penetration into the fungal cell. Depending on the type of alcohol and the alcohol-water ratio, the treatment can result in a fungistatic or a fungicidal effect. It was determined that 70:30 (v/v) ethanol-water mixture is most effective for a fungicidal effect, and is recommended by studies on written heritage collections.
• Application method: The efficiency of the treatment also depends on the fungal species, the contact time and the temperature, the higher the temperature is, the more efficient the treatment will be.   Several methods of implementation of the 70:30 (v/v) ethanol-water mixture have been studied for use on photographic materials:
  • By spraying: which results in a fungistatic effect with a 3 day delay of growth on paper.
  • By immersion: which results in a fungicidal effect on paper after 2.5 min, which was confirmed for chromogenic transparencies on cellulose acetate.
  • By vapours: which results in a fungicidal effect on paper and silver gelatin prints after two hours exposure.
• Effect on photographic materials: The effect of the treatment depends on the type of photographic material and the application method:
  • By immersion: The immersion of paper in ethanol-water 70:30 (v/v) solution does not modify its colour or mechanical properties. The immersion of chromogenic prints on resin coated paper in a ethanol-water 50:50 (v/v) solution causes partial dissolution of the dyes, the extent of the damage depended on the contact time. Similar effect was observed with the immersion of Ektachrome® films in an ethanol-water 70:30 (v/v) solution; as well as strong and irreversible planar distortions to the cellulose acetate support. However, the treatment plan developed by Pietsch and Fernandes with immersion of Kodachrome and Ektachrome films in successive ethanol-water baths (30:70 and 70:30 v/v) does not result in changes to colour or mechanical properties of the photographs.
  • By vapours: Various types of alcohols and water-alcohol ratios have been tested for vapour treatment.
    • Exposure to 50:50 and 95:5 (v/v) ethanol-water vapours for 21 days at 45°C results in modification of the silver image density, reddish coloration and yellowing of silver gelatin prints on baryta paper.
    • Exposure to 96:4 (v/v) butanol-water vapours for 48 hours at 26 °C does not induce colour changes to silver gelatin prints on baryta paper; however, treated samples were more faded and yellowed after aging than untreated samples. This treatment also caused some decrease of the gelatin degree of polymerization, resulting in a lower viscosity.
    • Exposure to 70:30 (v/v) ethanol-water vapours for 2 hours at 22°C did not modify colour or mechanical properties of paper. However, the treatment induced strong and irreversible planar distortions to cellulose acetate support and colour changes to chromogenic prints, the change being more important and recurrent in recent prints.
• Condition of the photograph: Treatment by vapour may be more suitable for photographs with fragile surface or poor physical integrity. A damaged photograph may be more vulnerable to treatment as the alcohol may react differently with damaged materials than with non-damages ones.
• Inscriptions: Some inks can be sensitive to ethanol and/or water. Treatment should be modified accordingly.

Gamma radiations

Advantages:

• Treatment of a large quantity of objects at once.
• No residues after treatment.

Disadvantages:

• Specialized installation required.
• High budget.
• Detrimental effect on some photographic materials (cumulative).
• Does not remove mold-related risks to human health.

Factors to consider:

• Radiation dose: Gamma radiation is obtained by nuclear fission of Cobalt 60, the exposure dose is expressed in Gray (Gy). The lethal dose for mold varies based on species, development stage (spores versus filaments) and the treatment conditions (temperature and oxygen levels). It has been found to be between 3 and 25 kGy, depending on the implementation conditions.
• Effects on photographic materials:
  • Physical effects: The treatment causes depolymerisation and oxidation of cellulose, proportional to the irradiation dose, similar to ones observed during aging, with lower folding endurance and tear resistance, increased yellowing, and embrittlement.  However, it does not modify the mechanical properties of cellulose nitrate and acetate, after exposure to 25 kGy. It also lowers gelatin emulsion viscosity after exposure to 2.2 kGy, but it does not modify the surface aspect of the emulsion after exposure to a dose up to 200 kGy.
  • Visual changes: Results obtained vary depending on the treatment implementation conditions, and where authors place the threshold for acceptable or visible color change. The treatment has been found to induce some color changes on albumen prints, x-ray films, monochrome cellulose acetate films, and chromogenic prints; as well as an increase in optical absorption of silver gelatin cellulose acetate films. Some authors observed more fading and yellowing of irradiated silver gelatin prints on baryta paper after light aging compared to control samples; whereas others did not find a difference. No change in color has been found after temperature aging of irradiated silver gelatin and chromogenic films on cellulose nitrate and acetate; nor after dark aging of chromogenic prints.
  • Susceptibility to fungal growth after treatment: Exposure to gamma radiation up to 100 kGy does not increase silver gelatin prints’ susceptibility to mold growth.

Commercial biocides

Buendia and Hoyos Velasco studied two commercially available biocides, Citricidal®️ and Éviter®️. The first one is composed of a citrus extract diluted in water or ethanol and the second one is composed of titanium dioxide nanoparticles diluted in ethanol.

Advantages:

• Commercially available
• No known toxicity for humans.

Disadvantages:

• Adverse short-term effect on photographic materials.
• Constant changes to products' composition.
• Does not remove mold-related risks to human health.

Factors to consider:

• Application method: The efficiency of both products depends on the fungal species and application method.
  • Citricidal®️: Application by spraying the biocides on both recto and verso of silver gelatin prints on baryta paper, three times, resulted in a fungistatic effect on four fungal species. Uneven application of the product, by spray, could explain the fungistatic results obtained. The product needs to be rinsed after application to avoid residues.
  • Eviter®️:  Application by spraying the biocides on both recto and verso of silver gelatin prints on baryta paper, three times, resulted in a fungistatic effect on one fungal species and a fungicidal effect on three fungal species. Uneven application of the product, by spray, could explain the fungistatic results obtained.
• Effects on photographic materials:
  • Citricidal®️: Leaves aluminum residues on the surface of silver gelatin prints on baryta papers, visible as amber coloured stains ; and a greasy texture on paper .  
  • Eviter®️: Leaves aluminum and chloride residues on the surface of silver gelatin prints on baryta papers and results in optical changes in brightness and gloss of the prints.
• Condition of the photograph: Citricidal®️ needs to be rinsed after application, which is not applicable to photographs with important mold growth and poor cohesion of constituent materials.

It is currently not recommended to use Citricidal®️ and Éviter®️ to treat photographic materials.

Ethylene oxide

Fungicidal properties of ethylene oxide are known since 1929, it was widely used in conservation in the 1960s; however, because of its toxicity, its use was restricted in the USA, Canada and some European countries. It is still in use in some countries (e.g. France).

Advantages:

• Treatment of a large quantity of objects at once.
• Fungicidal, insecticidal and bactericidal.
• Low cost

Disadvantages:

• Detrimental effect on some photographic materials.
• Long retention time in some photographic materials.
• High toxicity.
• Does not remove mold-related risks to human health.

Factors to consider:

• Gas mixture: At room temperature, ethylene oxide is a colorless gas, flammable and explosive in contact with air (at concentrations superior to 3%). To mitigate the risks of ignition or explosion, ethylene oxide is mixed with another gas: carbon dioxide, nitrogen, or hydrofluorocarbon derivatives, among others. The carbon dioxide and ethylene oxide mixture is the most economical, and several volume ratios (v/v) are used: 30:70, 15:85 and 10:90.
• Temperature and relative humidity during treatment: The efficiency of the treatment increases with temperature and with the humidify content of mold spores.
• Effect on photographic materials: Treatment with ethylene oxide breaks gelatin chains and  lowers the degree of polymerization, thus influencing the viscosity of the emulsion. Treatment of cellulose nitrate films results in slight shrinking of the film; and cellulosic materials are more hydrophilic after treatment, thus more susceptible to future fungal attack.
• Retention time: Ethylene oxide is easily absorbed by constituent materials, and can form chemical bonds particularly with plastic materials. Given its toxicity,  ethylene oxide retention time in materials must be taken into account for users safety. Seven days of off-gassing are enough for silver gelatin prints to reach a level of 2 ppm (legal threshold for human safety in France), plastic films (cellulose nitrate, cellulose acetate and polyester) require 42 days to reach the same threshold.

Historical treatments

Chemical treatments

Formaldehyde

Formaldehyde (CH₂O) is a colorless, odorless gas, which is carcinogenic to humans. Its fungicidal properties were studied in conservation in the 1960s. Various treatment times were recommended and it was widely used in libraries and archives. Further research in the 1990s evidenced the limit of this treatment because of the required off-gassing time, the risk of polymerization of formaldehyde on the surface of documents - creating a superficial film, and the adverse effects on cellulose - such as depolymerization, pH change, loss of flexibility and protein reticulation.

Phenol derivatives

Thymol (2-isopropyl-5-methylphenol) presents a genotoxic risk to humans. It can be used either as a gas or diluted in ethanol and results in fungistatic effects, as it does not kill fungal spores. It was widely used in conservation in the 1980s and the implementation varied from institution to institution, from 1 to 90 g/m³ concentration during 24 hours to 3 weeks. The implementation conditions are crucial for the efficiency of the treatment as thymol can promote mold growth if used at inefficient concentrations. Treatment with thymol can result in various detrimental effects on photographic materials: lower folding endurance, lower mechanical resistance, yellowing of paper, and oxidation of silver images.

O-Phenylphenol (C₁₂H₁₀O), is available under different trade names, such as Preventol, O Topane and Dowicide. In the 1980s it was recommended as a substitute for thymol for its lower toxicity to humans; however, it is toxic for aquatic environments. Early studies showed a fungicidal effect at low concentrations (10-50 ppm) in solution applied directly to the photograph or as a fumigant; however, as a gas it has low volatility and requires long off-gassing periods. Later studies at the end of 1980s and in the 1990s showed that O-Phenylphenol only has a fungistatic effect, and evidenced damages to photographic materials via paper discoloration, depolymerization of proteins, and effects equivalent to accelerated aging.

Quaternary ammonium salts

Quaternary ammonium salts (Quats) were discovered in 1851 and have been used for disinfection of photographic materials, using zinc fluorosilicate or Hyamine 1622 (Röhm & Haas) in an aqueous solution. Some Quats are highly toxic to humans with detrimental effects on the immune system. The disinfection treatment can be dangerous for water-damaged photographs as quats are applied by immersion in an aqueous solution. Furthermore, Hyamine 1622 adversely reacts with cyan dyes present in color photographs.

Kodak Film Cleaner

Kodak Film Cleaner (1,1,2-trichloro- 1,1,2-trifluoroethane) has some detrimental effects on humans. It was widely used to disinfect photographs and showed no adverse effect on the gelatin binders and plastic supports. This product was phased out after the 1994 Protocol of Montreal as an ozone-depleting substance.

Oxyden reduced atmospheres

Oxygen reduced atmospheres are widely used for the disinsectization of heritage collections. The method consists in reaching an oxygen level lower than 0.1% in a sealed environment, either by replacing oxygen with nitrogen or carbon dioxide (dynamic anoxia), or by introducing oxygen absorbers in the chamber (static anoxia). Since fungi are strict aerobic organisms, the removal of oxygen prevents their development, they enter into dormancy. The Centre de Recherche pour la Conservation des Collections (CRCC) tested anoxia treatments on 37 fungal strains: ten were completely destroyed but the others remained viable. Buendia tested static anoxia treatment, which was not successful to slow down or inhibit mold growth. 

Radiations

Radiations are electromagnetic waves characterized by a frequency and a wavelength. Their interaction with constituent materials and fungi depends on their energy levels.

Ultraviolet radiations

Ultraviolet (UV) radiation does not penetrate in materials, their wavelengths are between 10 and 450 nm. The fungicidal effect of UV radiation on paper documents is described in literature at various wavelengths. Flieder and Capderou mention UV-A (350-450 nm) whereas Nittérus talks about UV-C (230-275). Their use on photographic materials is not adapted as UV radiation has cumulative damaging effects, such as cellulose depolymerisation.

Micro-waves

Microwaves correspond to a wavelength of one meter to a few millimeters in the air, they are more commonly characterized by their frequency, in gigahertz. The production of microwaves generates heat through two mechanisms:

1. Electrical conduction: microwaves generate an electrical current in the conductive media, which creates heat by Joule effect;
2. Dielectric effect: polar molecules orient themselves according to the direction of the electric field, creating a mechanical oscillation. At the mechanical resonance frequency of the molecule (geometry and mass dependent) the amplitude is maximum, increasing the temperature. This effect is predominant in paper.

The first studies on the use of microwaves for the disinfection of heritage date back to 1947; however, this technique became applicable only in 1986 with the study by A. Brandt. The exposure to microwaves has a fungicidal effect provided that the temperature is above 55°C, the treated objects are thin (less than 2 cm) and humid. This fungicidal treatment does not damage paper; however, Gillet and Garnier report damages after treatment of gelatin emulsions weakened by mold.  

Further reading

General information

• Bailey H., Fungal contamination: a manual for investigation, remediation, and control, Jupiter: Building Environment Consultants, Inc., 2005.

This is a fairly comprehensive book consisting of 389 pages including an index, chapter summaries at the end of each chapter and summaries of guidelines from various government or national groups about the remediation of fungal infestations. The book covers issues related to the classification, structure and life cycle of fungi; identifying problem areas in buildings and how to sample of fungal growth and air quality, health effects, how to organize a team and the steps to take during mold remediation in a building. It provides good clear descriptions of what mold is and how it should be handled, including a couple of short sections on how to handle library materials (pp. 172-173), paper objects, and photographs (pp. 214-215) that have been affected by mold or water-damage. The section on antimicrobials (pp. 196-200) defines and differentiates between fungicides, disinfectants, fungistatics, and sporicides, giving examples of each and discussions of proper use. This book is a good resource for disaster planning in an emergency mold remediation project in a cultural institution.

• Mandrioli P., Caneva G., and Sabbioni C., Cultural heritage and aerobiology: methods and measurement techniques for biodeterioration monitoring, The Netherlands: Kluwer Academic Publishers, 2003.

This book presents a scientific examination of how airborne biological particles affect cultural material in a variety of indoor and outdoor environments, as well as how to monitor these particles to assess risk. It discusses specific types of materials and environmental factors that are prone to biodeterioration. There is also an in depth review of sampling techniques to identify the amount and kind of microbes present. This book offers helpful and detailed discussions of the affect of bioaersols on the specific environments of libraries and archives, museums, churches and hypogea.

• McCrady E., "Mold: the whole picture", Abbey Newsletter, 23, 4, 1999, Available online (accessed January 2023).

This article provides a general discussion of properties of mold focusing on their versatility and resiliency.

• Nyberg S., "Invasion of the giant mold spore", Solinet preservation leaflet, 2002, Available online (accessed January 2023).

This article provides a simplified summary of what mold is and details about how to detect and prevent it. The author discusses several treatment options for dealing with moldy objects. She does not recommend using chemical treatments, but does provide a list of chemicals that have been used as fumigants in the past along with their risks to human health and certain materials.

• Valentin N., "Microbial contamination in museum collections: organic materials", In Molecular Biology and Cultural Heritage, ed. C. Saiz-Jimenez, The Netherlands: Swets & Zeitlinger, 2003, pp. 85-91.

This article provides a brief literature review of non-chemical means of arresting or eliminating microbial growth in collection of organic materials. It has a chart of the most commonly found species of fungi and bacteria in museum collections. The author stresses the importance of controlling the water activity of an object as well as the relative humidity of the air. Most microbes will grow on organic objects with a water activity of 0.6 to 0.98. The author also advocates for using low temperatures (-20 ºC), nitrogen gas, and good ventilation as practical means to arrest microbial growth.

Biology of Fungi

• Caneva G., Nugari M. P., Salvadori O., Plant biology for cultural heritage: biodeterioration and conservation, Los Angeles: Getty Publications, 2008.

This book addresses the biological processes of fungi, bacteria, algae, and lichens; focusing on how they effect of a variety of cultural heritage material. The book has detailed descriptions of biodeterioratin as related to specific substrates, such as paper, photographs, leather, glass, and metal among many others found in cultural heritage collections. There are also useful sections on prevention and remediation for a variety of specific materials.

• Christensen C., The molds and man: an introduction to the fungi, 3rd ed., New York: McGraw Hill, 1965.

This book provides easy to understand and very comprehensive introduction to the biological functions of a variety of fungi. Much of the book has an agricultural focus, discussing the benefits and harms caused by fungi to plants and animals. There is one section that deals with fungi in buildings, but none that specifically addresses heritage material. There is an extensive index that could be helpful for looking up traits of a known fungus.

• Florian M-L., Fungal facts: solving fungal problems in heritage collections, London: Archetype Publications Ltd., 2002.

The majority of this book concentrates on explaining what fungi are and how they effect different types of material. Chapter 7 provides useful guidelines for treatment of objects affected by mold. The author concludes the book with discussions about sampling, disaster recovery, and implementing appropriate environmental controls.

Health and safety

• 2001. Mold and fungus. Hazardous Materials Assessment Inc., San Loreando. http://www.asbestos.org/mold/mold_frames.html (accessed Jan 2010).

This fact sheet is directed toward the general public facing problems with mold infestations in their homes. It provides bulleted lists of information including the types of mold that can cause health problems; common causes of increased moisture in a home that will cause mold outbreaks; and symptoms of mold exposure. The protective measures they suggest are wearing a N95 or TC-21C particulate respirator, gloves, clothing that can be discarded after clean up, work over short time spans to limit exposure, and to keep the area well ventilated. They also recommend cleaning procedures suitable for a private home, but not for remediation of mold on cultural artifacts. They consist primarily of disposing of porous objects that have been contaminated with mold, cleaning the affected area and any non-porous objects with soap and water, followed by a wet vacuum, and finally wiping down all surfaces with a 10% solution of household chlorine bleach.

• 2003. A brief guide to mold, moisture, and your home. Office of Air and Radiation Indoor Environments Division, Environmental Protection Acency. http://www.epa.gov/mold/moldguide.html (accessed Jan 2010).

This guide briefly talks about mold problems in private homes and stresses the importance of controlling moisture ingress to prevent mold outbreaks. If the area of mold is greater than ten feet square, is in a heating/ventilation/air conditioning (HVAC) system, or is caused by sewage they recommend hiring a contractor to deal with remediation. If the area is less than ten feet square they give guidelines to follow for clean up. They recommend wearing a N-95 respirator for particulate matter, wearing long gloves, and goggles that do not have ventilation holes. The EPA recommends using a mild detergent to clean mold and suggest using chlorine bleach only if someone who is at risk (infant, elderly, or immune-compromised) will be occupying that area. This is followed by a mold prevention section that gives tips for reducing moisture in a private home.

• 2009. Comments and suggestions from the American Industrial Hygiene Association on H.R. 1269. American Industrial Hygiene Association. http://www.aiha.org/news-pubs/govtaffairs/Documents/news05_HR1269-Conyers-Comments-05-04-05.pdf - (accessed Jan 2010).

This document is a reaction from the American Industrial Hygiene Association (AIHA) to the House Resolution 1269, an amendment to the United States Toxic Substances Safety Act proposed in 2005 (http://www.govtrack.us/congress/bill.xpd?bill=h109-1269). This amendment would classify mold and fungi as toxic substances subject to regulation and federal support programs. This document is particularly interesting in that the AIHA disagrees with the principle tenant of the bill, that certain molds should be classified as “toxic”. The AIHA states that while there are molds capable of producing mycotoxins, there has not been a clear link between these and adverse health affects. The AIHA says the definition of “toxic mold” is too broad and in reality adverse health affects are more akin to allergic reactions than exposure to toxic substances. Through out the document the AIHA also suggests that the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) be listed along with the federal agencies given authority in defining potential threats and courses of action due to fungal infestations. The AIHA disputes the bill’s tendency to generalize because actual health threats depend both on the specific species of mold as well as the individual exposed to the mold.

• Hardin, B. PhD, B. Kelman PhD, DABT, A. Saxon, MD. 2002. Adverse human health effects associated with molds in the indoor environment. American College of Occupational and Environmental Medicine. http://www.acoem.org/guidelines.aspx?id=850# (accessed Jan 2010)

Mold can affect people through three processes: allergy, infection, and toxicity. The most common allergenic indoor molds are Penicillium and Aspergillus; these are also the types most usually found on organic objects. About 10% of the population will have allergic reactions to these fungi. The authors also discuss some uncommon allergic symptoms caused by fungi, and say that often allergic reactions to dust mites or bacterial growth are misdiagnosed as fungal allergies. The molds which can cause serious infections in otherwise healthy individuals are: Blastomyces, Coccidiodies, Cryptococcus, and Histoplasma. The population who is most at risk for infection are people receiving chemotherapy or immunosuppressive drugs, AIDS pateients, and patients with uncontrolled diabetes. The authors stress that there is not evidence that inhaled mycotoxins have adversely affected the health of individuals in the indoor environment. Mycotoxins are large molecules and are non-volitile, but can be stirred up and inhaled as an aerosol. This aerosol exposure only becomes serious when it happens on a frequent basis in high doses, such as with agricultural workers moving affected grain. The authors put the point at which fungal growth can occur at 40% relative humidity.

• Rosol, M. 1994. Book mold data sheet. Acts Facts 8 (10): 3.

This review of the mold remediation guidelines published by The Center for Conservation of Art and Historic Artifacts in 1994 is mostly favorable. However, the author is careful to point out that using a water filtered vacuum, as recommended in the guidelines, will not actually filter out mold particles and only HEPA vacuums should be used.

• Salkinoja-Salonen, M. S., J. Peltola, M. A. Andersson, and C. Saiz-Jimenez. 2003. Microbial toxins in moisture damaged indoor environment and cultural assets. In Molecular Biology and Cultural Heritage, ed. C. Saiz-Jimenez. The Netherlands: Swets & Zeitlinger. 93-105.

This article provides information on the classes of toxins produced by microorganisms and the specific species of fungi or bacteria likely to produce them. Toxicity is difficult to predict because different strains of the same species may produce different toxins, several toxins, or none at all. Many toxins can be absorbed through the skin by direct contact and the authors recommend covering exposed skin. They also recommend wearing cotton gloves under nitrile or latex gloves as this will help prevent sorption of hydrophobic toxins, and that clothes should be washed at 60 ºC or higher with detergents that have enzymes. Of course, they also advocate for use of respirators, good ventilation, and caution not to stir up too much aerosol during the treatment of materials affected by microorganisms.

Mold remediation treatments

• Ali, Y, D. J. Dolan, E. J. Fendler, and E. L. Larson. 2001. Alcohols. In Disinfection, sterilization, and preservation. 5th ed. Edited by S.S. Block. Philadelphia: Lea and Febiger: 229-253.
  • This article is primarily written by and for those in medical professions. It begins with a history of the use of alcohol as an antiseptic. Alcohols are not sporicidal (they can inhibit germination, but this can be reversed), but are effective antimicrobial agents against a wide variety of microbes including fungi in its vegetative form. Alcohols attack microorganisms by causing protein coagulation/denaturation as well as interfering with cellular metabolism. For this to be effective some water must be present, pure alcohol can have a dehydrating effect, but will not be as antimicrobial as that with some water content. Chain length also affects the antibacterial effects. Tests have shown that propan-1-ol is the most effective water soluble alcohol, though ethanol is more commonly used.

• Baer, N. S. and M. H. Ellis. 1988. Conservation notes on thymol fumigation. The International Journal of Museum Management and Curatorship 7: 185-188.
  • Thymol is a fungicide that has been commonly used in paper conservation. It could be incorporated into wheat starch paste to prolong its usability. Paper objects were also exposed to tymol fumes or were housed with thymol impregnated papers to deter mold growth. By the time of the writing of this article, in 1988, the safety of the use of thymol was coming into question, and Baer reviews some of the recent literature about the use of thymol. Tymol posses a threat to the health of the conservators using it, as an irritant and possible carcinogen. It also has been seen to soften resin based media and coatings on objects, as well as to soften and yellow acrylic glazing. There have been instances of it recrystallizing on the surface of a treated object. The author brings up the need for more research to be done on o-phenyl phenol (OPP) as a possible substitute for thymol, but concludes with saying proper environment is really the best prevention.

• Block, S. S. 2001. Peroxygen Compounds. In Disinfection, sterilization, and preservation. 5th ed. Edited by S. S. Block. Philadelphia: Lea and Febiger: 185-204.
  • This article discusses the history of use and properties of peroxygen compounds as disinfectants. It has been found that hydrogen peroxide at 10-25% concentration has sporacidal properties, and is a good disinfectant at concentrations as low as 3%. Hydrogen peroxide is a safe disinfectant and occurs naturally in honey, milk, and the mucus membranes of our mouths. Hydrogen peroxide can form hydroxyl radicals, the strongest known oxidant. Tests have shown it is not significantly affected by change in pH, but will increase in efficacy with increased temperature and concentration. It can be applied as a liquid, gas, or plasma. The properties and applications of peracetic acid are also discussed.

• Calnan, C. 1985. Fungicides used on leather. Northhampton, UK: The Leather Conservation Centre.
  • This short publication summarizes the properties of fungicides commonly used by the leather industry and those used in conservation. There are several tables and appendixes that provide information on specific fungicides. The application of fungicides to leather is briefly discussed and it is concluded that more research needs to be done before industry fungicides can be used in conservation applications. No specific fungicides are recommended above others, but a comprehensive list is presented.

• Dychdala, G. R. 2001. Chlorine and Chlorine Compounds. In Disinfection, sterilization, and preservation. 5th ed. Edited by S.S. Block. Philadelphia: Lea and Febiger: 135-157.
  • This article is primarily written by and for those in medical professions. It begins with a history of the use of chlorine containing compounds as disinfectants. Chlorine is a very strong oxidizer. The exact mechanism of its biocidal action is not fully understood, but is thought to relate to the production of hypochlorous acid in aqueous solution. Thus chlorine solutions at a high pH is less effective than at a low pH. Raising the concentration of chlorine in solution or the temperature of the solution will also increase its biocidal activity. Different strains of microbial organisms will have different susceptibilities to the action of chlorine. The author includes specific discussion of the properties of a variety of chlorine containing compounds.

• Gillatt, J. 1991. Methods for the efficacy testing of industrial biocides – 1. Evaluation of wet-state preservatives. International Biodeterioration 27: 383-394.
  • This article examines the effectiveness of industrial biocides in five different substances: an emulsion paint, a metal working fluid, a starch-based adhesive, a bituminous emulsion, and a ready-mixed ceramic tile adhesive. The idea of wet-state resistance pertains to the material in solution before it has formed a film. It was found that a proprietary combination of heterocyclic compounds in a concentration of 0.10% completely stopped growth in the starch based adhesive and significantly stopped growth in the emulsion paint. This study does not directly correlate to uses in conservation, but does provide an avenue for further research.

• Goddard, P. A. and K. A. McCue. 2001. Phenolic Compounds. In Disinfection, sterilization, and preservation. 5th ed. Edited by S. S. Block. Philadelphia: Lea and Febiger: 255-281.
  • This article begins with a history of the production and use of phenolic compounds as antimicrobial agents. The effectiveness of the phenolic compound is dependent on the type and quantity of substitutions on the phenol ring. Thymol and o-phenylphenol are the phenolic compounds that have historically been used in conservation, this article written primarily for a medical audience offers insight into other compounds that may be safer and more effective, though much research needs to be done on the application of these in conservation.

• Gustafson, R. A., I. R. Modaresi, G. V. Hampton, R. J. Chepesiuk, G. A. Kelley. 1990. Fungicidal efficacy of selected chemicals in thymol cabinets. Journal of the American institute for Conservation 29 (2) 153-168.
  • This study tested the efficacy of eight different fungicides and found that only thymol and paraformaldehyde helped to prevent regrowth of mold cultures with paraformaldehyde performing slightly better in the prevention of conidia germination. However, the authors concluded that the health risks associated with paraformadehyde made it too hazardous to recommend. They also found ortho-phenylphenol, which had been recommended as a substitute for thymol, to be completely ineffective. They concluded that manual removal of the mold and environmental controls to be the most effective and safe procedures for remediation and prevention of mold growth.

• Haines, B. 1985. Fungicides and environmental controls for leather. In Recent Advances in Leather Conservation. Washington D.C.: Foundation for the American Institute for Conservation.
  • The paper presents the results of a study comparing thymol and o-phenyl phenol (OPP). Neither fumigant was able to stop growth of the test species. The author concludes the only way to stop fungal growth is to maintain an adequate environment and good housekeeping.

• Haines, J. H. and S. A. Kohler. 1986. An evaluation of ortho-phenyl phenol as a fungicidal fumigant for archives and libraries. Journal of the American Institute for Conservation. 25: 49-55.
  • The paper presents the results of a study comparing thymol and o-phenyl phenol (OPP). Neither fumigant was able to stop growth of the test species. The author concludes the only way to stop fungal growth is to maintain an adequate environment and good housekeeping.

• Isabell, L. H. 1997. The effects of thymol on paper, pigments, and media. Abbey Newsletter 21 (3). http://cool.conservation-us.org/byorg/abbey/an/an21/an21-3/an21-308.html (accessed February 2010)
  • This paper discusses the properties of thymol and its affect on paper, pigments, and media. The author concludes that thymol provides no lasting protection against fungal growth, and can discolor paper, parchment, inks, and organic pigments. The exact mechanism of this discoloration is unclear, though some ideas are proposed. The author recommends mechanical removal or immersion in ethanol as two possible alternatives for mold removal.

• Motylewski, K. 1994. Non-toxic fumigation and alternative control techniques for preserving cultural/historic properties and collections: notes on a conference. From the conference Pest, Insect and Fungus Management: Non-toxic Fumigation and Alternative Control Techniques for Preserving Cultural/Historic Properties and Collections. Technology and Conservation at the Harvard University Environmental Health and Safety Department. Cambridge, MA.
  • This paper provides brief summaries of a series of lectures given by professionals in the fields of conservation, entomology, and engineering. There is an interesting diversity of opinion on several topics such as the efficacy of anoxic environments on fungi and the safety of the use of fumigants. Some new ideas had to do with using borates, which are naturally occurring chemicals that prevent insect and mold infestations in some types of wood, and have been used for several decades in Australia and Europe.

• Nugari, M. P. and O. Salvadori. 2003. Biodeterioration control of cultural heritage: methods and products. In Molecular Biology and Cultural Heritage, ed. C. Saiz-Jimenez. The Netherlands: Swets & Zeitlinger. 233-242.
  • This article provides a summary of mechanical, physical, and chemical means of treating microorganisms on objects in cultural heritage collections. Mechanical techniques include manual removal and vacuuming. These techniques do not result in full removal of the fungal bodies and can sometimes result in damage to the object, but are recommended as a first step when appropriate, then folloed with physical or chemical removal as well. Physical methods consist of microwave, gamma, beta, Röntgen, X-ray, far ultraviolet radiation, as well as heating and freezing. Of the irradiation methosds, the authors feel that microwave radiation shows the most promise for use, but needs more research. The other forms of irradiation have been shown to cause harm especially to cellulosic or proteinacious materials. The most common biocide used currently are the quaternary ammonium salts (QUATs) followed by o-Phenylphenol (OPP). The author also review fumigants commonly used in the past cautioning against there use today. Unfortunately, viable fungal growth will still be present even after weeks and months of exposure in anoxic environments, so this is not a recommended treatment. In the application of any of these techniques careful consideration needs to be given to the specific substrate and the method and duration of application. There is no totally safe totally successful method.

• Ponce-Jimenez, M. D. P, F. A. Lopez-Dellamary Toral, H. Gutierrez-Polido. 2002. Antifungal protection and sizing of paper with chitosan salts and cellulose ethers: part 2, antifungal effects. Journal of the American Institute for Conservation 41 (3). 255-268.
  • This article describes a study comparing resilience to fungal attacks of papers sized with cellulose ethers and paper sized with chitosan salts. After the sample papers were sized they were inoculated with several common fungal cultures, which were allowed to germinate, then they were sterilized in alcohol and the zero-span tensile strength was used to evaluate deterioration. The chitosan salts did provide slightly more protection to the paper samples. The authors conclude that this is probably due to a mechanical barrier formed around the fibers by the chitosan, and that further testing is needed.

• Residori, L. and P. Ronci. 1986. Preliminary study on the use of ethylene oxide for the sterilization and disinfestations of books and documents. Paper Conservator, 10: 49-54.
  • This paper examines the safety and effectiveness of ethylene oxide fumigation. At the time the study was conducted there was no regulatory legislation in Italy for the use of ethylene oxide. The authors found that ethylene oxide could be detected outside of the fumigation chambers; that there was residual ethylene oxide present in treated objects, and that the treatment was not always effective.

• Smith, R. D. 1986. Fumigation quandary: more overkill or common sense? Paper Conservator, 10: 46-47.
  • This article review non-chemical means of controlling microbes and pests in library collections. The author recommends freezing, CO2 gas, and vacuum pressure.

• Weaver-Meyers, P. L., W. A. Stolt and B. Kowaleski. 2000. Controlling mold on library materials with chlorine dioxide: an eight-year case study. Abbey Newsletter 24 (4). http://cool.conservation-us.org/byorg/abbey/an/an24/an24-4/an24-402.html (accessed Jan 2010).
  • This article discusses the success that the Oklahoma Libraries have had using chlorine dioxide as a fungicide. The authors state that it is safer to use than most commonly used fungicides and has been approved for use in drinking water by the EPA. There were three ways in which chlorine dioxide has been employed: in solution wiped on affected objects and furniture; as a fog for overall infestation; and in time release packets, Aseptrol, for overall infestation.

• Wellheiser, J. G. 1992. Nonchemical treatment processes for disinfestations of insects and fungi in library collections. Munich: K. G. Saur.
  • This report discusses the processes currently under development for nonchemical disinfection. It looks largely at research from the fields of agriculture, health car, and the food industry. The author reviews the chemical treatments that have been used historically and then discusses possible non-chemical treatments in detail. The non-chemical treatments discussed are: deep freezing, high-energy (gamma) irradiation, low-energy (microwave) irradiation, modified atmospheres, and she also briefly touches on mechanical removal, heat, housing, biological controls (phermones, predators, sterility), environment, and maintenance. Unfortunately, the gamma irradiation is the only truly effective treatment for fungi, and it usually causes unacceptable levels of damage to the object being treated.

Case studies

• Caldararo, N and C. Griggs. 2001. Preliminary report on the conservation of slides with special reference to the removal of mold. Topics in Photographic Preservation 9: 97-102.
  • This study focused on finding a method to effectively remove mold hyphae without causing damage to the gelatin emulsion of 35 mm slides. Traditional solvent and mechanical methods of cleaning did not provide desirable results. A methodology was developed focusing on the properties of the cell walls of fungi, which are composed of chitin. Chitin is a polymer made up of repeating glucosamine units. Experiments with enzymes and NaCl to breakdown the chitin had only minimal success. The method the authors found that had the best results was to freeze the slides uncovered. When they were removed from the freezer a thin film of condensation formed on the slide, when this was wiped off with a swab. Most of the mold was removed and the emulsion was unaffected. The results were not totally predicable and often needed to be followed up with cleaning with 1:1 mineral spirits and water with 1% NaOH or Chitinase. The exact properties that allow for the success of the freeze cleaning are not fully understood.

• Lavédrine, B. 2003. A guide to the preventive conservation of photograph collections. Los Angeles: Getty Publications. 132-142.
  • This article provides a good overview of what mold is and how to detect and sample it. The author also writes briefly about fumigation for effected storage areas. He recommends quarternary ammonium products, such as zinc Hyamine 1622 for disinfecting silver gelatin photographs and fluorosilicate for silver gelatin or color photographs. However, to be effective, the objects must be immersed and often the binder is too compromised to do so. Treatment with ethylene oxide fumigation is discussed as it is still used in France.

• Lourenço, Miguel J. L.; Sampaio, José Paulo.2007. Microbial deterioration of gelatine emulsion photographs: a case study. Topics in photographic preservation Volume 12. 19-34.
  • Microbial deterioration is a common problem in photographic collections, and has been considered a major cause of deterioration. However, few studies have been carried out on this topic. Indeed, most of the literature is concerned with biodeterioration of archival documents in general, and this includes both micro and microorganisms. The environmental factors that promote this type of deterioration are well known and most of the published information is about prevention and control. There have been no detailed studies on the interactions between microorganisms, environment and the composition of photographic material. This study is focused on microbial deterioration of gelatine emulsion photographs, especially related to fungi. It was part of a global study of three collections in Lisbon, Portugal. The first part is a quantitative study on the microbial contamination of the Horácio Novais collection. The second is about induced contamination experiments of gelatine emulsion photographs. At the end these data will be analyzed taking into account the hypothesis that color materials are more susceptible to microbial deterioration than black and white ones. This hypothesis is based on the observations of several professionals working with photograph collections who report that, at least in plastic base supports (negatives and slides), color materials are frequently more contaminated than the black and white ones.
• Zyska, B.J.; Cieplik, Z.T.; Wojcik, A.R.; and Kozlowska, R. 1988. Microbial deterioration of historic glass plate negatives.” In book. Biodeterioration 7: Selected papers presented at the Seventh International Biodeterioration Symposium, Cambridge, UK, 6-11 September 1987, ed D. R. Houghton, D. R. et. al. New York: Elsevier Applied Science Publishers Ltd. 428-435.
  • This study identified 13 species of mold growing on a selection of 5,414 glass plate negatives from The Krieger collection in the Historical Museum of the City of Cracow. The collection includes plates with collodion and gelatin emulsions. In general, varnish layers were the most susceptible.

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