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CM 230 Deterioration of Cultural Heritage Prof. Dr. Ziad Al-Saad


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Title: CM 230 Deterioration of Cultural Heritage Prof. Dr. Ziad Al-Saad

CM 230 Deterioration of Cultural HeritageProf.
Dr. Ziad Al-Saad
  • Yarmouk University
  • Department of Conservation and Management of
    Cultural Resources

  • Our cultural heritage is made with almost all
    type of materials produced by the nature and used
    by men to realize several types of artefacts from
    very simple mono-components to complex structures
    integrating inorganic and organic matters.
  • These cultural heritage objects, even if made
    with the more resistant stones and metals, are
    influenced by the environmental parameters, which
    can modify their structure and composition

What Governs Deterioration of Cultural materials
  • The deterioration and preservation of materials
    depends on two things
  • The nature of the material
  • Environment surrounding the material.

  • Nature of the Material

What kinds of materials will I find in a museum
  • Museum objects are often divided into three
    material-type categories organic, inorganic, and
    composite. You must understand the properties of
    each of the materials in each of these

Organic Objects
  • Organic objects are derived from things that were
    once living plants or animals.
  • Based on C. Contains O, N, H
  • Materials are processed in a multitude of ways to
    produce the objects that come into your

Organic Objects
  • Various material types include wood, paper,
    textiles, leather and skins, horn, bone and
    ivory, grasses and bark, lacquers and waxes,
    plastics, some pigments, shell, and biological
    natural history specimens.

All organic materials share some common
  • They
  • Contain the element carbon
  • Are combustible
  • Are made of complicated molecular structures that
    are susceptible to deterioration from extremes
    and changes in relative humidity and temperature
  • Absorb water from and emit water to the
    surrounding air in an ongoing attempt to reach an
    equilibrium (hygroscopic)
  • Are sensitive to light
  • Are a source of food for mold, insects, and

Inorganic Objects
  • Inorganic objects have a geological origin. Just
    like organic objects, the materials are processed
    in a variety of ways to produce objects found in
    your collections.

Inorganic Materials
  • Material types include metals, ceramics, glass,
    stone, minerals, and some pigments.

All inorganic objects share some common
  • They
  • have undergone extreme pressure or heat
  • are usually not combustible at normal
  • can react with the environment to change their
    chemical structure (for example, corrosion or
    dissolution of constituents)
  • may be porous (ceramics and stone) and will
    absorb contaminants (for example, water, salts,
    pollution, and acids)
  • are not sensitive to light, except for certain
    types of glass and pigments

Composite Objects
  • Composite or mixed media objects are made up of
    two or more materials.
  • For example, a painting may be made of a wood
    frame and stretcher, a canvas support, a variety
    of pigments of organic and inorganic origin, and
    a coating over the paint.
  • A book is composed of several materials such as
    paper, ink, leather, thread, and glue.

Composite Objects
  • Depending on their materials, composite objects
    may have characteristics of both organic and
    inorganic objects.
  • The individual materials in the object will react
    with the environment in different ways.
  • Also, different materials may react in opposition
    to each other, setting up physical stress and
    causing chemical interactions that cause

What is inherent vice?
  • In addition to deterioration caused by the agents
    of deterioration, certain types of objects will
    deteriorate because of their internal
    characteristics. This mechanism of deterioration
    is often called inherent vice or inherent fault.
  • It occurs either because of the incompatibility
    of different materials or because of poor quality
    or unstable materials.

  • In nature, materials often possess
    characteristics that protect them from natural
    degradation. Their structure and composition may
    include features such as protective layers,
    insect and mold resistant chemicals, and
    photochemical protection.
  • Processing during object manufacture can remove
    these natural safeguards

Short-lived materials
  • Short-lived materials are often the result of
    manufacturing processes that do not consider the
    long-term stability of the items that were
  • Examples of impermanent materials with inherent
    vice include
  • cellulose nitrate and cellulose ester film
  • wood pulp paper
  • many 20th century plastics
  • magnetic media, including electronic records

Structural nature
  • Inherent vice can also be related to the
    structure of an object. Poor design, poor
    construction, or poor application of materials
    may cause structural failure. Examples of such
    damage include
  • drying cracks in paint improperly applied
  • broken or lost attachments
  • loose joints

  • The way an object was used or where it was stored
    or deposited before it comes into your collection
    may lead to inherent vice.
  • Here, damage and deterioration is caused by the
    original function of the object, its maintenance,
    or its environment.
  • Examples of inherent vice caused by history
  • accumulation of dissimilar paint layers, such
    as oil and latex
  • saturation in a wooden bowl that had been used
    as a container for oil
  • deposits of soluble salts in an archeological
    ceramic during burial

  • You may have trouble identifying deterioration
    caused by inherent vice because often there is
    little or no information on the selection and
    processing of materials, manufacturing details,
    and previous use of an object.
  • Train your critical eye by reviewing similar
    objects and by developing knowledge of object
    technology. Over time, you will become more
    proficient at identifying inherent vice.

What makes archeological objects different from
other materials commonly found in museum
  • The condition of these objects depends entirely
    on their reaction with the environmental
    conditions to which they have been exposed
    through time.
  • Underground the object reaches a kind of
    equilibrium with the surrounding soil. Then, when
    the object is excavated, it must adjust to a new
    and radically different environment.
  • Reactions can involve both physical and chemical

Regardless of the condition of the object before
excavation, the moment it becomes exposed it is
vulnerable to rapid deterioration. Figure I.1
illustrates the deterioration rate of
archeological objects
  • Deterioration of Museum Objects

What is deterioration?
  • Deterioration is any physical or chemical change
    in the condition of an object.
  • Deterioration is inevitable. It is a natural
    process by which an object reaches a state of
    physical and chemical equilibrium with its
    immediate environment.

Types of Deterioration
  • The types of deterioration can be divided into
    two broad categories physical deterioration and
    chemical deterioration. Both types often occur

What is chemical deterioration?
  • Chemical deterioration is any change in an object
    that involves an alteration of its chemical
  • It is a change at the atomic and molecular
  • Chemical change usually occurs because of
    reaction with another chemical substance
    (pollution, water, pest waste) or radiation
    (light and heat).

Examples of chemical change include
  • oxidation of metals (rusting)
  • corrosion of metals and stone caused by air
  • damage to pigments by air pollution or
    reaction with other pigments
  • staining of paper documents by adjacent acidic
  • fading of dyes and pigments

Examples of chemical change include
  • darkening of resins
  • darkening and embrittlement of pulp papers
  • burning or scorching of material in a fire
  • embrittlement of textile fibers
  • bleaching of many organic materials
  • cross-linking (development of additional
    chemical bonds) of plastics
  • rotting of wood by growing fungus

What is physical deterioration?
  • Physical deterioration is a change in the
    physical structure of an object.
  • It is any change in an object that does not
    involve a change in the chemical composition.
  • Physical deterioration is often caused by
    variation in improper levels of temperature and
    relative humidity or interaction with some
    mechanical force.

Examples of physical deterioration include
  • melting or softening of plastics, waxes, and
    resins caused by high temperature
  • cracking or buckling of wood caused by
    fluctuations in relative humidity
  • warping of organic materials caused by high
    relative humidity
  • warping or checking of organic materials caused
    by low relative humidity

  • shattering, cracking, or chipping caused by
  • stone cracking and scaling
  • structural failure (for example, metal fatigue,
    tears in paper, rips in textiles)
  • loss of organic material due to feeding by
    insects and/or their larvae
  • staining of textiles and paper by mold

  • Physical deterioration and chemical deterioration
    are interrelated. For example, chemical changes
    in textiles caused by interaction with light also
    weaken the fabric so that physical damage such as
    rips and tears may occur.

Why is it important to understand the
environmental agents of deterioration and how to
monitor them?
  • If you understand basic information about the
    chemistry and physics of temperature, relative
    humidity, light, and pollution, you will be
    better able to interpret how they are affecting
    your museum collections.
  • This chapter gives you a basic overview of these
    agents and describes how to monitor them. You
    will be able to tell how good or bad the
    conditions in your museum are and whether or not
    the decisions you make to improve the environment
    are working the way you expect.

  • In the past, simplified standards such as 50 RH
    and 65F were promoted. With research and
    experience, it is now understood that different
    materials require different environments. You
    must understand the needs of your collection for
    the long-term in order to make thoughtful
    decisions about proper care.

  • You will want to develop microenvironments for
    storage of particularly fragile objects. A
    microenvironment (microclimate) is a smaller area
    (box, cabinet, or separate room) where
    temperature and/or humidity are controlled to a
    different level than the general storage area.
  • Common microenvironments include
  • freezer storage for cellulose nitrate film
  • dry environments for archeological metals
  • humidity-buffered exhibit cases for fragile
    organic materials
  • temperature-controlled vaults for manuscript

  • Agents of Deterioration

  • What is temperature?
  • Temperature is a measure of the motion of
    molecules in a material. Molecules are the basic
    building blocks of everything. When the
    temperature increases, molecules in an object
    move faster and spread out the material then
    expands. When the temperature decreases,
    molecules slow down and come closer together
    materials then contract.
  • Temperature and temperature variations can
    directly affect the preservation of collections
    in several ways.

How does temperature affect museum collections?
  • Temperature affects museum collections in a
    variety of ways.
  • At higher temperatures, chemical reactions
    increase. For example, high temperature leads to
    the increased deterioration of cellulose nitrate
    film. If this deterioration is not detected, it
    can lead to a fire. As a rule of thumb, most
    chemical reactions double in rate with each
    increase of 10C (18F).
  • Biological activity also increases at warmer
    temperatures. Insects will eat more and breed
    faster, and mold will grow faster within certain
    temperature ranges.

How does temperature affect museum collections?
  • At high temperatures materials can soften. Wax
    may sag or collect dust more easily on soft
    surfaces, adhesives can fail, lacquers and
    magnetic tape may become sticky.
  • In exhibit, storage and research spaces, where
    comfort of people is a factor, the recommended
    temperature level is 18-20 C (64-68 F).
    Temperature should not exceed 24 C (75 F). Try
    to keep temperatures as level as possible.

Avoid Fluctuating Temperatures
  • Avoid abrupt changes in temperature. It is often
    quick variations that cause more problems than
    the specific level. Fluctuating temperatures can
    cause materials to expand and contract rapidly,
    setting up destructive stresses in the object. If
    objects are stored outside, repeated freezing and
    thawing can cause damage.
  • Temperature is also a primary factor in
    determining relative humidity levels. When
    temperature varies, RH will vary.

Relative Humidity
  • What is relative humidity (RH)?
  • Relative humidity is a relationship between the
    volume of air and the amount of water vapor it
    holds at a given temperature. Relative humidity
    is important because water plays a role in
    various chemical and physical forms of
  • There are many sources for excess water in a
    museum exterior humidity levels, rain, nearby
    bodies of water, wet ground, broken gutters,
    leaking pipes, moisture in walls, human
    respiration and perspiration, wet mopping,
    flooding, and cycles of condensation and

Relative Humidity
  • All organic materials and some inorganic
    materials absorb and give off water depending on
    the relative humidity of the surrounding air.
    Metal objects will corrode faster at higher
    relative humidity.
  • Pests are more active at higher relative
    humidities. We use relative humidity to describe
    how saturated the air is with water vapor. 50
    RH means that the air being measured has 50 of
    the total amount of water vapor it could hold at
    a specific temperature.

Relative Humidity
  • It is important to understand that the
    temperature of the air determines how much
    moisture the air can hold. Warmer air can hold
    more water vapor. This is because an increase in
    the temperature causes the air molecules to move
    faster and spread out, creating space for more
    water molecules.
  • For example, warm air at 25C (77F) can hold a
    maximum of about 24 grams/cubic meter (g/m3),
    whereas cooler air at 10C (50F) can hold only
    about 9 g/m3.

Relative Humidity
  • Relative humidity is directly related to
    temperature. In a closed volume of air (such as a
    storage cabinet or exhibit case) where the amount
    of moisture is constant, a rise in temperature
    results in a decrease in relative humidity and a
    drop in temperature results in an increase in
    relative humidity.
  • For example, turning up the heat when you come
    into work in the morning will decrease the RH
    turning it down at night will increase the RH.
  • Relative humidity is inversely related to
    temperature. In a closed system, when the
    temperature goes up, the RH goes down when
    temperature goes down, the RH goes up.

What is the psychrometric chart?
  • The relationships between relative humidity,
    temperature, and other factors such as absolute
    humidity and dew point can be graphically
    displayed on a psychrometric chart

  • The following definitions will help you
    understand the factors
  • displayed on the chart and how they affect the
    environment in your museum.
  • Absolute humidity (AH) is the quantity of
    moisture present in a given volume of air. It is
    not temperature dependent. It can be expressed as
    grams of water per cubic meter of air (g/m3). A
    cubic meter of air in a storage case might hold
    10 g of water. The AH would be 10 g/m3.
  • Dew point (or saturation temperature) is the
    temperature at which the water vapor present
    saturates the air. If the temperature is lowered
    the water will begin to condense forming dew. In
    a building, the water vapor may condense on
    colder surfaces in a room, for example, walls or
    window panes. If a shipping crate is allowed to
    stand outside on a hot day, the air inside the
    box will heat up, and water will and condense on
    the cooler objects.

  • Relative humidity relates the moisture content
    of the air you are measuring (AH) to the amount
    of water vapor the air could hold at saturation
    at a certain temperature. Relative humidity is
    expressed as a percentage at a certain
    temperature. This can be expressed as the
  • RH Absolute Humidity of Sampled Air/ Absolute
    Humidity of Saturated Air at Same Temperature x

  • In many buildings it is common to turn the
    temperature down in the evenings when people are
    not present.
  • If you do this in your storage space, you will be
    causing daily swings in the RH. Suppose you keep
    the air at 20C (68F) while people are working
    in the building. A cubic meter of air in a closed
    space at 20C (68F) can hold a maximum of 17
    grams of water vapor. If there are only 8.5 grams
    of water in this air, you can calculate the
    relative humidity.
  • The AH of the air 8.5 grams
  • The AH of saturated air at 20C 17.0 grams
  • Using the equation above
  • RH 8.5 x 100/17 50

  • 50 RH may be a reasonable RH for your storage
    areas. But, if you turn down the heat when you
    leave the building at night, the RH of the air in
    the building will rise rapidly. You can figure
    out how much by using the same equation. If the
    temperature is decreased to 15C (59F), the same
    cubic meter of air can hold only about 13 grams
    of water vapor. Using the same equation The AH of
    the air 8.5 grams
  • The AH of saturated air at 15C (59F) 13.0
  • RH 8.5 x 100/13 65
  • By turning down the heat each night and turning
    it up in the morning you will cause a 15 daily
    rise and fall in RH.

How do organic objects react with relative
  • Organic materials are hygroscopic. Hygroscopic
    materials absorb and release moisture to the air.
    The RH of the surrounding air determines the
    amount of water in organic materials. When RH
    increases they absorb more water when it
    decreases they release moisture to reach an
    equilibrium with the surrounding environment. The
    amount of moisture in a material at a certain RH
    is called the Equilibrium Moisture Content (EMC).

What deterioration is caused by relative humidity?
  • Deterioration can occur when RH is too high,
    variable, or too low.
  • Too high When relative humidity is high,
    chemical reactions may increase, just as when
    temperature is elevated. Many chemical reactions
    require water if there is lots of it available,
    then chemical deterioration can proceed more
  • Examples include metal corrosion or fading of
    dyes. High RH levels cause swelling and warping
    of wood and ivory. High RH can make adhesives or
    sizing softer or sticky. Paper may cockle, or
    buckle stretched canvas paintings may become too
    slack. High humidity also supports biological
    activity. Mold growth is more likely as RH rises
    above 65. Insect activity may increase.

What deterioration is caused by relative humidity?
  • Too low Very low RH levels cause shrinkage,
    warping, and cracking of wood and ivory
    shrinkage, stiffening, cracking, and flaking of
    photographic emulsions and leather desiccation
    of paper and adhesives and dessication of
    basketry fibers.

What deterioration is caused by relative humidity?
  • Variable Changes in the surrounding RH can
    affect the water content of objects, which can
    result in dimensional changes in hygroscopic
    materials. They swell or contract, constantly
    adjusting to the environment until the rate or
    magnitude of change is too great and
    deterioration occurs. Deterioration may occur in
    imperceptible increments, and therefore go
    unnoticed for a long time (for example, cracking
    paint layers). The damage may also occur suddenly
    (for example, cracking of wood). Materials
    particularly at high risk due to fluctuations are
    laminate and composite materials such as
    photographs, magnetic media, veneered furniture,
    paintings, and other similar objects.

  • Light causes fading, darkening, yellowing,
    embrittlement, stiffening, and a host of other
    chemical and physical changes.
  • Be aware of the types of objects that are
    particularly sensitive to light damage including
    book covers, inks, feathers, furs, leather and
    skins, paper, photographs, textiles, watercolors,
    and wooden furniture.

What is light?
  • Light is a form of energy that stimulates our
    sense of vision. This energy has both electrical
    and magnetic properties, so it known as
    electromagnetic radiation.
  • To help visualize this energy, imagine a stone
    dropped in a pond. The energy from that stone
    causes the water to flow out in waves. Light acts
    the same way. We can measure the wavelength
    (the length from the top of each wave to the
    next) to measure the energy of the light.

  • The energy in light reacts with the molecules in
    objects causing physical and chemical changes.
  • Because humans only need the visible portion of
    the spectrum to see, you can limit the amount of
    energy that contacts objects by excluding UV and
    IR radiation that reaches objects from light
  • All types of lighting in museums (daylight,
    fluorescent lamps, incandescent (tungsten), and
    tungsten-halogen lamps) emit varying degrees of
    UV radiation.

  • The unit of measurement is the nanometer (1
    nanometer (nm) equals 1 thousand millionth of a
    meter). We can divide the spectrum of
    electromagnetic radiation into parts based on the
  • The ultraviolet (UV) has very short wavelengths
    (300-400 nm) and high energy. We cannot perceive
    UV light. The visible portion of the spectrum has
    longer wavelengths (400-760 nm) and our eyes can
    see this light. Infrared (IR) wavelengths start
    at about 760 nm. We perceive IR as heat.

  • The energy in light reacts with the molecules in
    objects causing physical and chemical changes.
  • Because humans only need the visible portion of
    the spectrum to see, you can limit the amount of
    energy that contacts objects by excluding UV and
    IR radiation that reaches objects from light
  • All types of lighting in museums (daylight,
    fluorescent lamps, incandescent (tungsten), and
    tungsten-halogen lamps) emit varying degrees of
    UV radiation.

  • This radiation (which has the most energy) is the
    most damaging to museum objects. Equipment,
    materials, and techniques now exist to block all
    UV. No UV should be allowed in museum exhibit and
    storage spaces.
  • The strength of visible light is referred to as
    the illumination level or illuminance. You
    measure illuminance in lux, the amount of light
    flowing out from a source that reaches and falls
    on one square meter.

Reciprocity law
  • When considering light levels in your museum you
    should keep in mind the
  • reciprocity law. The reciprocity law states,
    Low light levels for extended periods cause as
    much damage as high light levels for brief

  • The rate of damage is directly proportional to
    the illumination level multiplied by the time of
  • A 200-watt light bulb causes twice as much
    damage as a 100-watt bulb in the same amount of
    time. A dyed textile on exhibit for six months
    will fade about half as much as it would if left
    on exhibit for one year.

  • So if you want to limit damage from light you
    have two options
  • reduce the amount of light
  • reduce the exposure time

What are the standards for visible light levels?
  • You can protect your exhibits from damage caused
    by lighting by keeping the artificial light
    levels low.
  • The human eye can adapt to a wide variety of
    lighting levels, so a low light level should pose
    no visibility problems. However, the eye requires
    time to adjust when moving from a bright area to
    a more dimly lighted space. This is particularly
    apparent when moving from daylight into a darker
    exhibit area. When developing exhibit spaces,
    gradually decrease lighting from the entrance so
    visitors eyes have time to adjust.
  • Do not display objects that are sensitive to
    light near windows or outside doors.

Basic standards5 for exhibit light levels are
  • 50 lux maximum for especially light-sensitive
    materials including
  • - dyed organic materials
  • - textiles
  • - watercolors
  • - photographs and blueprints
  • - tapestries
  • - prints and drawings
  • - manuscripts
  • - leather
  • - wallpapers
  • - biological specimens
  • - fur
  • - feathers

  • 200 lux maximum for less light-sensitive
    objects including
  • - undyed organic materials
  • - oil and tempera paintings
  • - finished wooden surfaces
  • 300 lux for other materials that are not
    light-sensitive including
  • - metals
  • - stone
  • - ceramics
  • - some glass

  • In general don't use levels above 300 lux in your
    exhibit space so that light level variation
    between exhibit spaces is not too great.

  • In order for collections to be seen and used in
    various ways (for example, long-term exhibit,
    short-term exhibit, research, teaching) you
    should take into account a variety of factors
  • light sensitivity of the object
  • time of exposure
  • light level
  • type of use
  • color and contrast of object

Dust and Gaseous Air Pollution
  • Air pollution comes from contaminants produced
    outside and inside museums.
  • Common pollutants include dirt, which includes
    sharp silica crystals grease, ash, and soot from
    industrial smoke sulfur dioxide, hydrogen
    sulfide, and nitrogen dioxide from industrial
    pollution formaldehyde, and formic and acetic
    acid from a wide variety of construction
    materials ozone from photocopy machines and
    printers and a wide variety of other materials
    that can damage museum collections.

pollutants are divided into two types
  • particulate pollutants (for example, dirt,
    dust, soot, ash, molds, and fibers)
  • gaseous pollutants (for example, sulphur
    dioxide, hydrogen sulphide, nitrogen dioxide,
    formaldehyde, ozone, formic and acetic acids)

What are particulate air pollutants?
  • Particulate pollutants are solid particles
    suspended in the air.
  • Particulate matter comes both from outdoor and
    indoor sources. These particles are mainly dirt,
    dust, mold, pollen, and skin cells, though a
    variety of other materials are mixed in smaller
  • The diameter of these pollutants is measured in
    microns (1/1,000,000 of a meter). Knowing the
    particulate size is important when you are
    determining the size of air filters to use in a
  • Some particles, such as silica, are abrasive.
    Pollen, mold and skin cells can be attractive to
    pests. Particulates are particularly dangerous
    because they can attract moisture and gaseous

Three forms of Damage Mechansims
  • A source for sulfates and nitrates (These
    particles readily become acidic on contact with
  • A catalyst for chemical formation of acids
    from gases
  • An attractant for moisture and gaseous

What are gaseous air pollutants?
  • Gaseous pollutants are reactive chemicals that
    can attack museum objects.
  • These pollutants come from both indoor and
    outdoor sources.

Outdoor pollutants
  • Outdoor pollutants are brought indoors through a
    structures HVAC system or open windows.
  • There are three main types of outdoor pollution
  • sulfur dioxide (SO2), and hydrogen sulphide
    (H2SO) produced by burning fossil fuels, sulfur
    bearing coal, and other organic materials
  • nitrogen oxide (NO) and nitrogen dioxide
    (NO2), produced by any kind of combustion, such
    as car exhaust as well as deteriorating
    nitrocellulose film, negatives, and objects
  • ozone (O3), produced by sunlight reacting with
    pollutants in the upper atmosphere and indoors by
    electric or light equipment, such as photocopy
    machines, printers, some air filtering equipment

  • When sulfur and nitrogen compounds combine with
    moisture and other contaminants in the air,
    sulfuric acid or nitric acid is produced.
  • This acid then causes deterioration in a wide
    variety of objects. Ozone reacts directly with
    the objects causing deterioration.

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The main sources of indoor air pollution
  • wood, which can release acids
  • plywood and particle board, which give off
    acids from wood and formaldehyde and acids from
  • unsealed concrete, which releases minute
    alkaline particles
  • some paints and varnishes, which release
    organic acids, peroxides, and organic solvents
  • fabrics and carpeting with finishes, such as
    urea-formaldehyde, and wool fabrics that release
    sulfur compounds.
  • glues, used to attach carpets, that can
    release formaldehyde
  • plastics that release plasticizers and harmful
    degradation products such as phthalates and acids

  • Museum objects themselves may also contribute to
    indoor air pollution.
  • Examples of sources of pollutants from museum
    objects include
  • celluloid and other unstable plastics used to
    produce many 20th-century objects
  • cellulose nitrate and diacetate plastic, used
    for film
  • pyroxylin impregnated cloth used for book
  • residual fumigants, such as ethylene oxide

  • Object Materials Deterioration Primary by Air

  • Metal corrosion/tarnishing sulfur oxides

  • stone surface erosion and discoloration

Soluble Salts and Deterioration of Archeological
  •  Porous archeological artifacts such as ceramics,
    stone, bone, and ivory often contain soluble
    salts. Ground water and seawater can carry these
    salts into the pores of the artifact during
    burial leaving them behind when the water
  • After excavation, these salts can crystallize at
    or just below the surface of the artifact causing

  • A variety of descriptive terms are used for this
    damage including spalling , flaking, powdering,
    and sugaring.
  • The force of growing crystals can break apart the
    surface of bone, stone, ceramics and other porous
    materials so that detail is lost.
  • In bad cases it can remove the entire surface of
    an artifact.
  • In the worst cases, it can destroy an artifact.

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Soluble Salts and Insoluble Salts
  • Conservators divide the salts that are deposited
    in and on an artifact during burial into two
  • insoluble salts and soluble salts.

  • Soluble salts will dissolve in moisture in the
    air. This property is known as deliquescence.
  • The salts can move through the porous structure
    of an artifact as moisture is drawn out through
  • As the salts reach the surface of the artifact
    they may crystallize as white, often furry
    growths on the surface.
  • If the surface is less porous than the
    underlying structure they can crystallize just
    below the surface. These crystals exert immense
    pressure and may cause the surface layer to spall

Salt Damage to Porous Materials
  • Salt damage is largely attributable to two
    mechanisms crystallization of salts from
  • hydration of salts, that can exist in more than
    one hydration state.
  • The growth of salt crystals within pores can
    cause stresses, which are sufficient to overcome
    the stone's tensile strength
  • When the migration of the salt to the surface of
    the stone is faster than the rate of drying, the
    crystals deposit on the top of the external
    surface and form visible efflorescences, which do
    not damage the stone. When the migration is
    slower than the drying rate, the solute
    crystallizes within the pores, at varying depth,
    causing crumbling and powdering of the stone.

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Why does salt speed up corrosion?
  • Water is required for corrosion and salt speeds
    up the process.
  • Corrosion is the transfer of electrons from one
    substance to the other so salt present in water
    improves the capability of water to carry
    electron through redox reactions.
  • Rusting in metals is the oxidizing of metal to
    metal oxide. Water acts as the medium to transfer
    the electrons and salt helps the corrosion
    process to speed up the process.

Insoluble salts
  • Insoluble salts are not truly insoluble but
    will take days or weeks to dissolve in water.
    They are not deliquescent and so will not cause
    further damage after excavation.
  • Insoluble salts can, however, be quite
    disfiguring, and may require removal for
    identification or reconstruction of an artifact.

  • Chlorides
  • Carbonates
  • Nitrates
  • Sulphides
  • Sulfates
  • Phosphates

Identifying Salts
  • In order to identify the salts conservators use
    analytical methods such as spot tests or x-ray
  • Soluble salts are visible as a white growth on
    the surface of an artifact. In newly excavated
    material, they often form first along cracks or
    abraded areas of a surface. Often they can look
    like a white bloom or haze on the surface. As the
    crystals continue to grow and form they will
    extend further from the surface and appear as a
    white powder or even look somewhat like table
    salt. They may have a soft, fuzzy feel if

  • Deterioration of Archaeological Materials

  • Deterioration of Ceramics, Glass, and Stone

Physical Forces
  • The agents of deterioration that can have the
    most profound effect on ceramics, glass, and
    stone in museum collections are direct physical
  • If ceramic or glass objects are dropped, they
    usually break. Most stone will chip, crack, or
    break if dropped. Cumulative damage can occur
    with improper handlingpieces can be chipped off
    and residues left from handling. Some ceramic,
    glass, and stone objects also have flaws, either
    inherent or from their previous use, that make
    them vulnerable to heat or moisture.

  • Deterioration of Pottery and Ceramics

How ceramics were made?
  • Ceramic objects are made up of a mixture of
    natural materials that are combined, formed into
    shape by a variety of processes, and transformed
    by heat to create a solid, brittle substance not
    found in nature.
  • Different firing temperatures produce objects
    with a vast range of hardness and porosity.

Most clay objects are a mixture of materials
  • Clay is a fine-grained mineral--the smallest
    particles produced by the weathering of certain
  • When heated to a high temperature it chemically
    and physically changes to a hard, brittle
  • Adding fluxes such as soda, mica, potash,
    magnesia, or lime lowers the firing temperature
    of clay.
  • These fluxes may also be found in natural clay
    deposits. Non-plastic additives (temper) are
    added to clay to reduce shrinkage and cracking
    during firing and drying. Temper also increases
    porosity in the finished object.
  • These basic materials are mixed together by the
    potter to produce a heterogeneous plastic mass
    that is then formed into the ceramic object.

Ceramics are loosely divided into four groups.
These groups are based ontheir firing
temperature, clay type, and physical
  • Adobe or mudbrick is an unfired clay mixture.
    This material is often used for building, but
    mudbrick objects, such as cuneiform tablets and
    sculpture, are often found in museum collections.

  • Earthenware is a low-fired clay mixture. These
    objects are fired between about 950-1100ºC. At
    this low temperature sintering occurs but not
  • Earthenware is generally soft and scratches
    easily. It is often red in color from naturally
    occurring iron in the clay brown, black, and
    yellow are also common colors.
  • Earthenware has the following characteristics
  • - It is porous and will readily absorb water
    unless glazed.
  • - The structure is often granular in appearance
    with numerous coarse
  • particles.
  • - There is a clear distinction between the
    ceramic body and any glaze
  • layer.

  • Stoneware is fired between 1100-1350ºC.
    Stoneware objects are partially vitrified. Common
    colors for stoneware are buff, brown, and gray.
  • Stoneware has the following characteristics
  • - It is partially vitrified and less porous than
  • - It is harder and denser than earthenware and
    does not scratch easily.
  • - If tapped lightly, the body will give a
    distinctive ring.
  • - The glaze and body are tightly adhered.

  • Porcelain is fired at very high temperatures,
    usually above 1300ºC.
  • Porcelain is made of a special clay called
    kaolin. This clay is difficult to work and must
    be fired under precise conditions.
  • Porcelain can be formed into objects with thin,
    complex structures.
  • Porcelain has the following characteristics
  • - The body is completely vitrified and impervious
    to water (nonporous).
  • - The clay body is white and translucent and
    extremely hard and
  • brittle.
  • - When tapped lightly, the object rings with a
    higher tone than
  • stoneware.
  • - In cross-section, glaze and body are nearly

  • A general rule of thumb is that lower-fired
    ceramics will easily absorb water, while
    higher-fired ceramics will absorb little or no
  • To test this, you can use a small paintbrush to
    apply a little water to an unglazed area of
    ceramic, and watch to see if it is drawn in.
    Because high-fired ceramics are less likely to
    absorb water, they have fewer salt problems

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  • Ceramics may have different surface finishes,
    coloration, or impressed designs.
  • A glaze is a thin layer of clear or colored glass
    on the ceramic surface. A slip is usually more
    like a thin layer of clay and has a matte
    appearance and is a different color than the clay
    body. Ceramics may be coated with other materials
    as well, including paints and inks.

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  • Ceramics are decorated most commonly with a slip
    or glaze that is fired on, or melted onto the
    surface when it is fired. Ceramics with a
    fired-on overall glaze or other decorations are
    impervious to normal variations in temperature
    below several hundred degrees.
  • These fired-on decorations also help protect
    ceramics from humidity.
  • In recent decades, some ceramics have been
    initially fired but later decorated with paint or
    some other decoration that is never fired. These
    unfired decorations are very fragile and are
    easily damaged by exposure to water, heat, or

  • Repaired ceramics may suffer damage from
    temperature and humidity extremes.
  • Broken ceramics reassembled with adhesive have
    weaknesses. Most adhesives soften and give way at
    elevated temperatures. Ceramic pots with repairs
    may sag, collapse, or fall apart if they are
    stored in a hot area, such as an attic or a
    building that does not have air conditioning.

  • Salts can damage or destroy ceramics. The clay
    may have originally contained a significant
    amount of salt, and other types of earth added to
    adjust the properties of the clay may include
  • Water or foods stored in ceramic vessels often
    leave salts behind. Contact with seawater or
    burial below ground can also introduce salts.

  • Fluctuating humidity levels aggravate the harmful
    effects of salts in ceramics.
  • Above 60 percent relative humidity, the salts
    dissolve and move around inside the ceramics.
    When the ceramics dry, the salts migrate to the
    surface and are left behind when the water
  • This is called salt efflorescence. Efflorescence
    generates tremendous forces, pushing off areas of
    glaze or decoration and even breaking up entire

  • Generally, mold will not grow on ceramics, and
    insects will not attack them.
  • In very wet conditions, however, mold or lichens
    may grow on ceramic surfaces, although the mold
    will not digest the ceramic itself. Insects will
    eat food residues left on ceramics and will eat
    materials applied after firing. However, proper
    environmental conditions prevent mold, lichens,
    and insects.

  • Light is not harmful to ceramics as such, but
    pigments used in surface decoration could be
    damaged by over exposure.

  • Some old repair methods have caused damage in the
    long term. Very strong adhesives were used in the
    past, but in ageing they have been found to
    discolour and shrink, and in shrinking a layer of
    the ceramic can be pulled away from the body of
    the pot.
  • Today's conservators have a wide range of
    adhesives from which to choose. Those used with
    ceramics will usually be weaker than the ceramic
    body to prevent too strong a join from causing
    further damage.

What flaws might I find in ceramic objects?
  • It is important to recognize the flaws that may
    occur during the manufacturing process so you can
    separate flaws from damage or active

  • Deterioration of glass

The Nature of Glass Objects
  • Glass has been used for personal adornment,
    containers, construction materials, and a host of
    other purposes throughout the last four
  • In order to understand how to preserve glass
    objects, you must understand how they are

What materials make up thestructure of glass
  • The basic materials of glass are silica and
    alkaline oxide (also known as flux).
  • Silica generally comes from sand or crushed
    flint. The flux interacts with the silica and
    lowers the melting temperature.
  • Typical fluxes include lead, calcium, potassium,
    and sodium oxides.
  • Other oxides (iron, copper, cobalt, manganese,
    chromium and nickel) are added as colorants. When
    melted, this mix of materials flows readily to
    form various shapes.

Glass component Relative amount () Silica
(glass former) 6075 Soda (modifier) 3015 Lime
(stabilizer) 15 8 Iron oxides (generally added
unintentionally) 10less than 1
  • The basic process for making glass, although not
    the actual technology, has changed little since
    antiquity. Over the centuries the technology has
    advanced, being continuously improved and refined
    beyond recognition
  • Six main manufacturing stages are involved in the
    glassmaking process
  • 1. Selecting the raw materials
  • 2. Comminuting and mixing the raw materials
  • 3. Heating and melting the mixture
  • 4. Fabricating, that is, forming and shaping
  • 5. Annealing the objects
  • 6. Finishing

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  • Glass is a unique materiala rigid liquid.
  • A liquid is an amorphous material that does not
    have an organized, crystalline structure. Most
    materials, such as metals, form a crystalline
    lattice as they cool from a liquid to a solid
  • Molten glass, however, cools too quickly for this
    structure to form. The structure is "frozen" into
    a random network of molecules.
  • Glass is rigid and brittle at room temperature.
    Depending on the materials included in the mix,
    it can be transparent, translucent, or opaque.

Lattice VS Amorphous
Glazes and Enamels
  • Glazes and enamels are also glasses with small
    differences in composition from bulk glass.
  • Glazes are applied to ceramics enamels are
    usually applied to a metal support.
  • Glazes and enamels are generally opaque and fired
    at lower temperatures than glass.

What flaws might I find in glass objects?
  • Flaws can be introduced during the manufacturing
    process. Learn to distinguish these flaws from
    active deterioration problems. Look for

  • They may also be added intentionally for
    decorative effect. A few isolated bubbles will
    not weaken a glass object, however, a cluster of
    bubbles might. The shape of the bubbles gives
    clues to the direction that the object was worked
    in the molten state.

  • Inclusions or foreign bodies These are more
    noticeable in translucent glass. Often these
    flecks come from contamination in the crucible or
    impurities in the raw materials. Small inclusions
    may disrupt the surface and look of an object,
    but they will not affect its strength.
  • .

Compositional flaws
  • Compositional flaws Sometimes these are not
    apparent for many years.

How does glass deteriorate?
  • Most damage to glass is mechanical. It is easily
    broken and chipped.
  • Water is the major chemical agent of
    deterioration for glass and the susceptibility of
    glass to deterioration depends greatly on its
    original chemical structure.

  • Glass, a supercooled liquid, is in a metastable
    state, that is, an apparently stable condition
    that may be perturbed by external conditions and
    undergo unpredictable changes, so that the
    supercooled liquid may be converted to a solid.
  • When glass is made from a well-balanced mixture
    of former, modifier, and stabilizer, it is
    remarkably stable.

  • Environmental changes may, however, cause the
    glass to crystallize, or, as the condition is
    known, to devitrify, that is, to lose its
    vitreous (glassy) properties.

  • Glass exposed to the environment or buried in the
    soil under dry conditions, even for long periods
    of time, is usually stable and undergoes very
    little devitrification or decay.
  • The more humid the environment or burial site,
    the more easily glass decays and the more
    extensively it devitrifies.
  • Extended periods of alternating dry and wet
    conditions may result in periodic decay effects
    and the formation of devitrified layers, first on
    the outer faces and then throughout the bulk of
    the glass

  • The chemical decay of glass often starts when its
    alkaline components, soda, potash, or lime, are
    leached by water from the surrounding of the
    glass (leaching is the process of extraction of
    the soluble components of a solid by their
    dissolution, usually in water but also in mild

Decay of Glass
  • The tendency to, and the extent of decay of glass
    are determined mainly by its composition, the
    environmental temperature and humidity, and/or
    the surrounding water conditions at the location
    sit of the glass. Salts in, and the pH of
    groundwater, and even microorganisms with which
    glass is in contact, alter its rate of decay.

Stages of Glass Decay
  • Various stages in the decay of glass have been
  • dulling, which entails the loss of clarity and
    transparency, is the simplest frosting, the
    formation of a network of small cracks on the
    surface follows

Stages of Glass Decay
  • Strain cracking, the occurrence of small cracks
    running in all directions, is a more advanced
    form of decay that may result in the partial or
    total disintegration of glass

Stages of Glass Decay
  • Frosting and strain cracking
  • Take place particularly when water is abundant
    the water leaches from the glass most of the soda
    and potash and part of the lime, leaving behind
    only thin layers of hydrated silica.

Stages of Glass Decay
  • The final stages of such a decay process may
    result in the glass becoming just a residue of
    generally separate, flaky, highly porous, layers
    of hydrated silica displaying a sugarlike
    appearance that eventually totally disintegrates .

Crusts of weathered glass. The deterioration of
glass and the formation of weathered layers under
humid or wet conditions is a rather complex
process. Seasonal variations of temperature and
of the amount of environmental moisture may
provide the trigger that initiates the glass
weathering process. Still, the final product of
the process are opaque layers composed mainly of
hydrated silica (silica is the main component of
Partial leaching and devitrification
  • , Although basically damaging, often enhance the
    appearance of old glass they give origin to
    iridescence, the display of rainbow-like
    variegated colors when illuminated old glass is
    moved or turned. Iridescence generally occurs on
    ancient glass that has been recurrently exposed
    to seasonal variations, in some climates in
    yearly cycles, of temperature and humidity.
  • Such cyclic processes result in the formation, on
    the outer, exposed faces of the glass, of very
    thin layers of decay products (composed mainly of
    hydrated silica) the thickness of single layers
    has been measured and found to vary in the range
    0.315 microns. Light incident on these layers
    causes interference between beams reflected from
    their front and back surfaces and gives rise to
    the variety of colors often seen on ancient glass

Crizzling Glass
  • Crizzling is a fine network of surface cracks
    that turn glass translucent.
  • Moisture in the air reacts with unstable glass
    containing too little lime
  • (calcium oxide). The moisture causes potassium
    and sodium in the glass structure to leach out.
    As the structure weakens, small cracks appear.

Weeping Glass
  • Weeping is caused by leaching sodium or
    potassium absorbing water on the surface of
    deteriorating glass to form sodium or potassium
  • These compounds accumulate on the surface of the
    glass and may give it a greasy feeling. The
    hydroxides may also react with carbon dioxide in
    the atmosphere to form carbonates, which can
    absorb even more water.

  • Crusty or waxy deposits on the surface, which
    may have a white crystalline appearance, are
    typically seen on ethnographic beadwork and may
    be a reaction of the glass deterioration products
    to oils in adjacent leather.

  • Iridescence is a rainbow-like effect on the
    glass surface and is an indication of
    deterioration. The colors are visible when light
    is diffracted between the air-filled layers of
    deteriorated glass.

  • Devitrification is the production of small
    areas of crystal growth in the otherwise
    amorphous glass structure. These crystals may be
    intentionally produced during production as they
    give glass good thermal shock resistance.
    Unintentional devitrification is caused by
    unstable glass with too much alumina or too much


  • The factors considered to be among the leading
    causes of building stone deterioration include
  • salt crystallization
  • aqueous dissolution
  • frost damage,
  • microbiological growth
  • human contact
  • original construction

Salt Crystallization
  • Crystallization of salts within the pores of
    stones can generate sufficient stresses to cause
    the cracking of stone, often into powder
    fragments. This process is considered to be the
    major cause of stone deterioration

  • Closely related to the crystallization of salt is
    damage caused by salt hydration and by
    differential thermal expansion of salts

  • The resistance of stone to salt damage is
    dependent on the pore size distribution and
    decreases as the proportion of fine pores
  • Crystallization damage caused by highly soluble
    salts, such as sodium chloride and sodium
    sulfate, is usually manifested by powdering and
    crumbling of the stone's surface

  • Less soluble salts such as calcium sulfate form
    glassy, adherent films which cause spalling of a
    stone's surface

  • A major source of salts in urban environments is
    the reaction between air pollutants and stone.
    For example, limestone can react with sulfur
    dioxide to ultimately produce calcium sulfate.
    Other sources of salts include ground water
    airborne salts sea spray and chemical cleaners

Aqueous Dissolution (Pollution)
  • Carbonate sedimentary stones e.g., limestone),
    carbonate-cemented sandstone, and marbles are
    types of stone that are susceptible to
    dissolution by water acidified with dissolved
    carbon dioxide, sulfur dioxide, and nitrogen
    oxides problem

  • It has been reported that the rainwaters in many
    urban areas in the United States and Europe are
    sufficiently acidic to accelerate the weathering
    of exposed building stone.
  • In areas where the rainwater is relatively free
    from pollutants, the dissolution of most common
    building stones is usually not a serious problem

Frost Damage
  • Certain stones which are exposed to freezing
    temperatures and wet conditions may undergo frost
    damage. The frost susceptibility of a stone is
    largely controlled by its porosity and pore size

  • Of stones with a given porosity, those with the
    smallest mean pore size will generally be the
    most susceptible to frost damage. Frost
    resistance also generally decreases with
    increased available porosity pore volume which is
    accessible to water.

  • Some European stone conservators believe that in
    their countries frost damage is not an important
    process in the deterioration of stone. They
    regard frost damage as a secondary process, e.g.,
    frost damage may be responsible for the final
    fragmentation of stone damaged by other
    processes, such as salt crystallization. However,
    because of the use of possibly more
    frost-susceptible stone and more severe climates,
    frost damage may be an important factor in the
    southern and eastern part of Jordan.

Microbiological Growth
  • The attack of stone by a variety of plants and
    animals has been reported including roots of
    plants, ivy vines, microorganisms, boring
    animals, and birds. Of these, microorganisms
    appear to be the most destructive.

  • Some types of bacteria, fungi, algae, and lichens
    produce acids and other chemicals which can
    attack carbonate and silicate minerals
  • . It appears that under certain environmental
    conditions attack by microorganisms can be a
    serious problem . However, it seems that many
    conservators feel that such instances are
    uncommon and that microorganism growth usually
    takes place in stone which had been partially
    deteriorated by other processes.

Human Contact
  • Because of an increasing interest by the public
    in historic structures, the effects of human
    contact upon the condition of stone, as well as
    all other building materials, is of growing
  • For example, stone floors are gradually worn by
    foot traffic, stones are damaged by people either
    collecting souvenirs or poking into soft stone ,
    and graffiti removal has become an important
    maintenance problem . It is conceivable that
    human contact may become a major problem
    challenging the ingenuity of both stone
    conservators and maintenance specialists.

Tourism and Urban development
Original Construction
  • The durability of stone structures also depends
    on factors encountered during their original
    construction including proper design, good
    construction practices, and proper selection of
    materials. Unfortunately, these are factors over
    which the preservation scientist has no control.
  • However, the same mistakes should not be
    repeated in repairing or restoring historic
    structures. For example, normal steel and cast
    iron anchors, dowels, reinforcing rods, etc.,
    were often used in the construction or repair of
    stone structures. Certa
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