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Consultancy Agency and Workshop for Preservation, Conservation and Restoration of Books,
Archival Materials and Graphic Arts. Preservation Management for Libraries and Archives.
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Deterioration

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Physico-chemical agents of deterioration.

We consider physical and chemical treats of deterioration together because in a lot of cases their mutual influence on each other and on the process of deterioration is inseparable.

Physico-chemical agents can be divided in two categories, i.e. these that are inherent to the object and those of external origin. As inherent we consider all agents that were originally present in the raw materials used to produce it or were added to it while manufacturing it. We consider as external agents all those that are not original to the object but have influenced it through the ages and eventually still do.

Agents Inherent to the object

  • Lignin

Basic components of library and archival materials can be responsible for their own deterioration. The best-known example is lignin in ground wood paper. Lignin is an impurity of ground wood paper, which is responsible for the browning, and acidification of the paper. The lignin is destructed under influence of oxygen in the air. The process is being catalyzed by light. In the dark the reaction occurs slower but does not stop.
  • Metal particles

Metal particles are sometimes inherent to the concerned object. In paper it is mostly an involuntary addition during the production process. Metal particles from the machines involved for grinding the wood or preparing the pulp can accidentally be introduced.
Or the particles can be part of the water used for the papermaking. These particles are oxidized by the oxygen in the air. This is the so-called metal corrosion.

Metal particles are also inherent to magnetic tapes, compact discs and photographic material.

    • The chroomdioxide particles in magnetic tapes can react with poly-urethane en accelerate deterioration by hydrolysis
    • The alumininiumcoating in compact discs can oxidize and cause CD rot
    • Photographic material can deteriorate when the silver halide components react to unstabilized residual developing chemicals
  • Chemicals

A lot of chemicals are added to the different archive and library materials.


© De Zilveren Passer.    Larger image (61Kb).
    • They vary from fillers, coatings and finishers to pigments in paper.
    • Cellulose-acetate films contain acetic acid and a catalyst as sulfuric acid.
    • Developing chemicals and pigments can influence the rate of deterioration of photographic materials
    • Magnetic tape often contains solvents, plasticizers, wetting agents, stabilizing agents and lubricating agents.

External agents.

  • Temperature and Relative Humidity

These two agents are best considered together since they affect deterioration in close relation to each other. In fact relative humidity is more important than temperature, but the difference in temperature determines the influence of relative humidity on the different materials.

There are no ideal temperature and relative humidity for storage of library and archive materials. Nevertheless there are matched values which are being considered as safe as possible for the different materials involved. It is generally accepted that regular fluctuations in temperature and relative humidity are more damaging than a constant somewhat higher or lower level of both.
    • Temperature and Fire
    • Temperature influences the process of deterioration by catalyzing chemical reactions. One generally accepts that every increase of 10°C speeds up chemical reactions by a factor 2 to 4.
    • It also influences the relative humidity because the maximum amount of water that can be dissolved in air is related to temperature. With the same amount of water in the air, relative humidity increases when temperatures
      drop and decreases when temperatures rise.

    Fire damage.
    © De Zilveren Passer.    Detailed view (74Kb).

    • Fire is of course an important agent of deterioration since it simply destroys the materials involved.
    • Relative Humidity and Water
    • Relative humidity affects deterioration because it can increase the process of hydrolysis.
    • Increase in relative humidity also increases possible development of microorganisms on the objects. These mechanisms become more important when temperatures are also rising.
    • Water is damaging to several materials because it causes delamination, migration and dissolving of glues, inks, pigments and additives, and when inadequately dried causes deformation and distortion, staining, loss of information and great risk of developing microbiological attacks.
  • Light, Ultraviolet and other radiation

Light is a very important cause of deterioration. The process involved is often called photochemical degradation or photolysis.

Investigation has determined that the area of the light spectrum beneath 500 nanometer is the most damaging. This involves the area of the UV radiation up to 400 nanometer and the lowest part of the visible spectrum between 400 and 500 nanometer.
    • Light
    • Although UV wavelengths seem to be the more damaging light in general can cause quite some deterioration when objects are subjected to high light intensities even for short periods of time or to long periods of exposure even at lower intensities.
    • The impact of light exposure will also be dependent of the basic components of the materials involved. Ground wood paper, photographic materials, iron gall inks, colour pigments and several other materials will be more susceptible to exposure than others.
    • Ultraviolet radiation
    • UV radiation is produced by the Sun and by different kinds of artificial light sources. Since natural UV radiation beneath 300 nanometer is absorbed by the atmosphere of the earth, occurring deterioration occurs by the remaining radiation
    • The impact of UV radiation is also dependent on the basic materials involved.
    • Other radiation
    • Alpha, beta, gamma and röntgen radiation seem to have a negative influence on organic polymers.
  • Atmospheric Pollution

Atmospheric pollution is a major cause of deterioration of library and archive materials. Certain chemical compound are being formed in the air in a natural way, but man adds also an enormous quantity of these and other compounds to the air.

When concentration becomes inconvenient one talks about atmospheric pollution. It is being caused as well by waste products of industrial origin as by exhaust fumes form cars and combustion of house heating products. The concentrations of these products are variable with the season of the year, the implantation of industry, density of traffic and weather conditions.

Very noxious products are sulphur dioxide, carbon dioxide, nitrogen monoxide and dioxide. They react with water to form acids that accelerate hydrolysis in different materials. They also react with other chemicals, which are basic components of library and archive materials.

Ordinary dust contains all kinds of materials that can be abrasive, soiling and damaging information carriers. Moreover it is mostly a good breeding ground for all kinds of biological agents.
  • Metal particles

Metal particles can be introduced in writing materials by using inks as iron gall ink or colour pigments as copper in copper green. These metal particles oxidize over time and corrode the material on which they have been used. In combination with water they accelerate hydrolysis. They cause acidification, staining and corrosion and in the end they may fall out of their support, leaving a hole.
  • Electro-magnetic fields

All magnetic media are susceptible to magnetic fields. External magnetic fields can lead to demagnetisation and subsequent loss of information. This is especially a problem with computer materials as floppy-discs and hard discs.

 		 
What's related:

Agents of deterioration:

General info
Biological
Human intervention

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