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Contaminants
Type Chemical Direct or Indirect damage Both Affects Mixed Key risks Airborne pollutants SO2, NOx, O 3 , particulate matter, off- gassing from storage materials, chemical reactions, corrosion, discoloration, acidification, surface deposits, degradation of materials Prevention strategies Air filtration systems, use archival quality materials, regular cleaning, sealed display cases, activated charcoal filters, environmental monitoring, proper ventilation, avoid PVC and acidic materials in storage Related weeks
Examples 1. Airborne Contaminants
- Gases: ◦ Sulfur dioxide SO₂) – damages leather (“red rot”). ◦ Hydrogen sulfide H₂S – tarnishes silver and copper. ◦ Nitrogen oxides NOₓ) – acidify paper. ◦ Ozone O₃) – causes oxidation and embrittlement of organic materials.
- Particulates: ◦ Soot and smoke – settle into porous surfaces. ◦ Dust – abrasive and attracts pests. ◦ Sea salts – cause corrosion and salt crystallization.
- Contact Contaminants Transferred through direct contact with harmful materials.
- Acidic storage materials (e.g., certain woods or boards)
that cause corrosion.
- Migrating substances (plasticizers from PVC, oils from fingerprints).
- Non-archival adhesives that stain and become acidic over time.
- Staining solids that transfer dyes or chemicals to nearby surfaces.
- Intrinsic Secondary) Contaminants Produced from within the object as it degrades.
- “Vinegar syndrome” – acetic acid released from degrading cellulose acetate.
- Nitric acid from cellulose nitrate breakdown.
- Internal acidic components (e.g., iron gall ink) that damage materials from within.
- Efflorescence – internal salts that migrate and crystallize on the surface. Mastery level Not started
📌 Definition (CCI)
According to the Canadian Conservation Institute CCI , contaminants (often referred to as pollutants) are a range of compounds—including gases, aerosols, liquids, or solids—of either natural or human-made origin that are known to have adverse effects on heritage objects. The agent of deterioration "Contaminants" describes substances that come into contact with an object and either react chemically with its components or leave behind physical traces that undesirably change the object's appearance or properties.
Key Aspects of the Definition
Physical States: They manifest as gases (air pollution), liquids (spilled drinks, cleaning solvents), or solids (dust, soot, adhesive tape). Origin: They can be anthropogenic (industrial emissions, traffic, cigarette smoke) or natural (salts from the sea, volcanic gases, or hydrogen sulfide from marshes).
Mechanical Damage: Dust acts as an abrasive; the act of cleaning it off can cause scratches or material loss, especially on fragile surfaces. Catalytic Action: Deposited particles can be hygroscopic (attracting moisture) or oily, which can initiate or accelerate chemical decay or fungal growth on the surface.
2. Chemical Mechanisms
Contaminants react with an object's components to cause irreversible structural changes through several specific processes: Oxidation: Oxygen O 2 Involved in the oxidation of organic materials like polymers and skins, often after being "photo-excited" by radiation. Ozone O 3 A powerful oxidant that attacks double bonds between carbon atoms. This leads to the embrittlement of rubber and the fading of many artists' colorants. Photo-oxidation: Occurs when light and UV radiation accelerate chemical processes involving pollutants. Hydrolysis: This reaction involves water vapor or acids and is a primary cause of degradation in cellulose-based materials like paper, film, and textiles. Autocatalysis: In materials like cellulose acetate (vinegar syndrome) or cellulose nitrate, the hydrolysis process releases acids that stay within the material and further accelerate its own decay. Acidification and Corrosion: Gaseous Acids: Nitrogen oxides NOx and sulfur dioxide SO2) react with air moisture to form nitric and sulfuric acids. These acids weaken leather ("red rot"), acidify paper, and corrode metals. Organic Acids: Acetic and formic acids (emitted by wood like oak or certain glues) are particularly aggressive toward lead and calcareous materials (shells, fossils), forming white powdery corrosion or salt efflorescence. Tarnishing: Reduced-sulfur gases H 2 S) react rapidly with silver and copper to form a dark sulfide layer. This reaction is so fast that its rate
is determined solely by how quickly the gas reaches the metal surface.
3. Environmental Influences on Mechanism Rates
The speed of these chemical mechanisms is highly dependent on the surrounding indoor climate: Temperature: A general rule of thumb is that the reaction rate doubles for every 5°C increase in temperature. Relative Humidity RH High RH levels increase the reaction rate for most chemical processes, such as the rusting of iron or the hydrolysis of paper. High humidity is also required for certain contaminants to migrate between materials (e.g., iron gall ink transferring to adjacent pages).
🧪 Chemical / Physical Process
The agent of deterioration known as contaminants (or pollutants) involves substances—whether gases, aerosols, liquids, or solids—that interact with heritage objects to cause either chemical degradation or physical change.
Chemical Processes
Chemical processes occur when pollutants react with the material components of an object, often leading to irreversible damage. These reactions are frequently accelerated by high temperatures and relative humidity. Oxidation: Strong oxidants like ozone O 3 attack organic materials, particularly by breaking double bonds between carbon atoms, which leads to the embrittlement and cracking of rubber and the fading of colorants. Oxygen O 2 itself participates in many oxidative processes, such as the rusting of iron or the chemical decay of polymers and skins. Acidification: Gaseous pollutants such as sulfur dioxide SO 2 and nitrogen dioxide NO 2 react with moisture in the air or within an object to form acids. This leads to the acidification of paper and the breakdown of textiles and leather. A specific example is "red rot" in vegetable-tanned leather caused by sulfur dioxide. Corrosion and Tarnishing: Reduced sulfur gases like hydrogen sulfide H 2 S are highly reactive and cause the rapid tarnishing of silver and copper. Volatile organic acids, such as acetic acid emitted from wood products like oak, cause severe white powdery corrosion on lead objects.
🎨 Most Vulnerable Materials
The vulnerability of heritage objects to contaminants (pollutants) depends on their material composition and the specific type of pollutant involved. While many materials react to contaminants, the sources highlight several groups as being particularly susceptible.
Highly Vulnerable Metals
Metals are primarily affected by oxidative processes, leading to tarnishing and corrosion. Lead: Identified as the most sensitive material to acetic acid (emitted by woods like oak and certain paints), which causes it to develop a white, powdery surface crust. Silver: Highly vulnerable to reduced-sulfur gases (like hydrogen sulfide), which cause rapid yellowing and eventually black tarnishing. Copper and Brass: Sensitive to sulfur dioxide and hydrogen sulfide (tarnishing) as well as organic acids, which can cause green corrosion. Iron: Prone to rusting, especially when moisture (water vapor) acts as a pollutant to facilitate the reaction.
Sensitive Organic Materials
Organic materials often suffer from chemical degradation such as oxidation or hydrolysis, resulting in discoloration, yellowing, and eventual embrittlement. Paper and Books: Vulnerable to acidification from nitrogen oxides and sulfur dioxide. Paper containing alum (intrinsic pollutant) or in contact with acidic wood/cardboard is at even higher risk. Vegetable-Tanned Leather: Highly susceptible to sulfur dioxide, which causes a weakening of the fibers known as "red rot". Natural Rubbers: Ozone is a powerful oxidant that specifically attacks the double bonds in vulcanized natural rubber, causing rapid embrittlement and cracking. Artists' Colorants: Many pigments and dyes (especially plant-based ones) fade or discolor when exposed to ozone, nitrogen dioxide, and sulfur dioxide.
Calcareous Materials and Glass
Shells, Fossils, and Limestone: These calcareous materials are highly susceptible to organic acids (acetic and formic acid), which react with the calcium carbonate to cause efflorescence (salty, snowy flakes). Glass: Sodium-rich glass can react with organic acids, leading to salt crystallization or surface phenomena like "weeping" and crizzling.
Objects Difficult to Clean
Solid contaminants like dust and soot are considered high-risk for materials that are physically fragile or porous, as cleaning them can cause irreversible mechanical damage. Fragile Surfaces: Powdery pigments, feathers, and butterfly wings. Porous/Textured Materials: Ivory and painted objects with micro-cracks where fine particles can become lodged. Magnetic Media: Audio/video tapes and digital media are highly sensitive to dust, which causes read errors, signal loss (dropouts), and surface scratching.
Inherently Unstable Materials (Intrinsic Sources)
Some materials are their own worst enemies, producing pollutants as they degrade: Cellulose Acetate and Nitrate: These release acetic and nitric acids respectively, which accelerate their own destruction (autocatalysis) and corrode nearby materials. Flexible PVC Releases plasticizers that migrate to the surface, making the object sticky and potentially staining adjacent materials.
🛡 Preventive Measures
Preventive measures for contaminants (also referred to as pollutants) follow a systematic approach designed to reduce the dose—the concentration of the pollutant multiplied by the duration of exposure—that reaches an object. The primary strategies are organized into the following levels of control:
1. Avoid: Eliminating Sources
Oddy Testing: Test new display materials in a sealed jar with metal coupons at 60°C for four weeks to check for harmful emissions. Dosimetry: Use advanced electronic dosimeters to measure the cumulative dose of pollutants over time. Dust Monitoring: Place clean glass plates in different areas and use a microscope or gloss meter to assess the rate of dust accumulation.
4. Respond and Recover: Active Mitigation
If pollutants are detected at high levels, active measures must be taken to lower their concentration. Sorbents Scavengers): Place active or passive sorbents like activated carbon, silica gel, or charcoal cloth inside enclosures to soak up harmful gases. Dilution: Increase ventilation with clean air if the pollutant source is internal to the room. Environment Control: Lower the temperature and relative humidity RH . As a rule of thumb, the chemical reaction rate of pollutants doubles for every 5°C increase in temperature. Maintaining RH below 30%significantly reduces the reaction rate of organic acids. Inert Environments: For highly valuable items, use enclosures filled with non-reactive gases like nitrogen or argon to eliminate oxygen and moisture.
🔗 Interaction with other agents
The effects of contaminants (pollutants) on heritage objects are rarely isolated; they frequently interact with and are exacerbated by other agents of deterioration. These interactions can accelerate chemical decay, cause physical damage, or attract further threats to the collection.
1. Interaction with Incorrect Indoor Climate
The surrounding climate is the most significant factor in how contaminants affect materials. Temperature: Chemical reaction rates involving pollutants are primarily determined by temperature; as a rule of thumb, the reaction rate doubles for every 5°C increase. High temperatures also accelerate the off-
gassing of volatile organic compounds VOCs from construction materials like wood and adhesives. Relative Humidity RH High humidity acts as a catalyst for many chemical processes, such as the rusting of iron or the acidification of paper through hydrolysis. Furthermore, high RH can cause deposited dust to "cement" to an object's surface, making it nearly impossible to remove without causing mechanical damage. Conversely, very low RH (below 30%) can significantly slow down the reaction rates of organic acids.
2. Interaction with Light, UV, and IR
Photo-oxidation: UV and visible radiation can "photo-excite" molecules, initiating photo-oxidation processes that make organic materials like rubber and polymers more vulnerable to gaseous pollutants like ozone. Visibility: High light levels or specific lighting angles (like raking light) can make dust and soiling much more visible and distracting to the viewer. Dust accumulation on lamps can also pose a fire risk due to overheating.
3. Interaction with Pests
Food and Shelter: Dust and particulate accumulation provide both shelter and a food source for insects and fungi. Excrement from pests (like fly specks) contains chemically active contaminants that can permanently stain or react with susceptible surfaces. Pesticide Residues: Chemical treatments used to eliminate pests often leave behind toxic residues or solvents that act as long-term contaminants on the objects they were meant to protect.
4. Interaction with Physical Forces
Abrasion: Solid contaminants like sea salts or industrial dust are often hard and sharp; the physical act of handling or cleaning/dusting an object can cause surface scratches and material loss through friction. Packaging and Support: Physical barriers like crates or display cases can inadvertently become sources of contaminants if they are made from emissive materials like MDF or acidic cardboard.
5. Interaction with Fire and Water
Ozone $O_ 3 $ Found in photochemical smog or produced by photocopiers; it causes oxidation and embrittlement of organic materials like rubber. Particulates/Solids: Soot and smoke: From urban transportation or candles; can become encrusted in the cracks of porous objects like ivory. Dust: Acts as an abrasive, a pest attractant, and a source of read errors for magnetic media. Sea salts: Natural airborne particles that cause corrosion and efflorescence.
Contact Contaminants
These are transferred through direct physical contact between a harmful material and an object: Acidic Materials: Poorly chosen storage materials like oak shelving or certain chipboards that emit acetic acid, leading to the severe corrosion of lead objects. Migrating Substances: Plasticizers from flexible PVC, or oils and fatty acids from fingerprints and greasy leather. Adhesives: Non-archival "original" adhesive tapes that stain paper or become acidic over time. Staining Solids: Rubber tubes or dyed fabrics that transfer colorants or chemicals to adjacent surfaces.
Intrinsic (Secondary) Contaminants
These contaminants are generated from within the object itself as it degrades: Vinegar Syndrome: Degrading cellulose acetate (found in old films and negatives) releases acetic acid, which further accelerates its own decay and corrodes nearby metals. Nitric Acid: Released during the hydrolysis of cellulose nitrate, making the material extremely brittle and hazardous. Internal Chemicals: Acidic components like iron gall ink or alum in paper that "eat" the substrate from the inside out.
Efflorescence: Salts already present in ceramics, shells, or minerals that migrate to the surface and crystallize when relative humidity fluctuates.
🧪 Acidificació i corrosió Gasos com SO₂ i NOₓ formen àcids. Debilitament del paper. “Red rot” en cuir vegetal. Corrosió de metalls (plata, coure, plom). 🌡 Factors que acceleren el dany 🌡 Temperatura: la velocitat de reacció es duplica cada 5 °C. 💦 Humitat relativa alta: accelera corrosió i hidròlisi. 💡 Llum UV i visible: activa processos de foto-oxidació. 🧱 Materials més vulnerables
🪙 Metalls
Plom: molt sensible a lʼàcid acètic. Plata: sʼennegreix amb gasos sulfurosos. Ferro: rovell amb humitat. 📚 Materials orgànics Paper i llibres: acidificació. Cuir vegetal: red rot. Cautxú natural: es torna fràgil amb ozó. Colorants: es descoloreixen. 🐚 Materials calcaris Petxines, fòssils, pedra calcària → eflorescències salines. 🎞 Materials inestables Acetat de cel·lulosa → “síndrome del vinagre”. PVC flexible → migració de plastificants (superfícies enganxoses). 🛡 Estratègies de conservació preventiva Evitar Allunyar col·leccions de fonts contaminants.
No usar materials emissius (fustes àcides, MDF . Prohibir menjar i fumar. Bloquejar Vitrines hermètiques. Filtres (carbó actiu). Embalatges adequats. Ús de guants. Detectar Tests Oddy. Cupons metàl·lics indicadors. Monitoratge de pols. Respondre Sorbents (carbó actiu, sílice). Reduir temperatura i HR 30% frena àcids orgànics). Atmosferes inertes (nitrogen). 🔗 Interacció amb altres agents Els contaminants rarament actuen sols: 🌡 Clima incorrecte → accelera reaccions. 💡 Llum → activa foto-oxidació. 🐛 Pols → atrau insectes. 🔥 Incendis → fum i gasos corrosius. 💧 Inundacions → taques i sals. 🎨 Vandalisme → grafits, vessaments. 🏷 Pèrdua dʼetiquetes → dissociació dʼinformació. 🎯 Idea clau Els contaminants poden ser invisibles però acumulatius. El control no és eliminar-los del tot, sinó reduir la dosi que arriba a lʼobjecte.
Dissociation
Type Human Direct or Indirect damage Indirect Affects Mixed Key risks Loss of documentation, separation of objects from their context, missing labels, poor cataloging, loss of provenance, inability to locate objects, degraded research value, administrative chaos Prevention strategies Robust documentation systems, database management, proper labeling, regular inventories, standardized cataloging procedures, backup systems, trained staff, clear acquisition protocols, digital documentation, location tracking Exam probability Medium Mastery level Not started
📌 Definition (CCI)
According to the Canadian Conservation Institute CCI , dissociation is the agent of deterioration that results from the natural tendency for ordered systems to fall apart over time. It is defined as the loss of objects, object- related data, or the ability to retrieve or associate objects and data.
Key Characteristics
The "Metaphysical" Agent: Unlike the other nine agents of deterioration that primarily affect an object's physical state, dissociation affects its legal, Dissociation 1
intellectual, and cultural aspects. Definition of "Loss": In this context, loss is defined as becoming unable to retrieve on demand that which is wanted. Magnification Effect: A unique characteristic of this agent is that the loss of value to even a few objects—such as the cross-contamination of research samples—can compromise and reduce the value of the collection as a whole.
Manifestations of Dissociation
Dissociation occurs when the link between a physical object and its context or non-material attributes is broken. It generally manifests in three ways: Loss of objects: Physical items are misplaced, misfiled, or accidentally discarded because they are not adequately identified. Loss of data: Information such as provenance, research notes, or legal titles is lost, often due to transcription errors, illegible recording, or the failure to migrate digital files to modern formats. Loss of association: The link between the object and its data is severed, such as when labels or tags detach, crumble, or become unreadable.
Origins and Risks
The concept was added to the agents of deterioration framework in the 1990 s by Robert Waller (originally under the names "Loss" or "Custodial neglect"). Risks are categorized into three types: rare and catastrophic single events (e.g., accidental disposal of an entire collection), sporadic severe events (e.g., undocumented loans), and continual processes(e.g., the gradual fading of labels or the departure of staff with unrecorded knowledge).
🔎 Mechanism of Deterioration
The mechanism of deterioration for dissociation differs fundamentally from the other ten agents of deterioration because it primarily affects the legal, intellectual, and cultural aspects of an object rather than its physical state. It is often described as the "metaphysical agent" because the damage occurs to the association between the physical object and the information that gives it context and meaning. Dissociation 2
