GD22/10 - Newspaper page from HIV/AIDS campaign

A newspaper that has discoloured over time, especially along the edges and folded areas

Deterioration of modern paper

Often paper made in the past 50 years shows greater deterioration than papers made 500 years ago. For example, this newspaper page (right) found in the HIV/AIDS collection has discoloured and become brittle.

Paper deterioration can be caused by both internal and external factors.

Internal causes of paper deterioration

The raw materials and the manufacturing process of paper can cause degradation.

Raw materials

In Europe, early papers were made from cotton, linen and hemp rags which were relatively stable and generally made good quality papers. However, as the demand for paper grew, papermakers began to use different materials and methods which resulted in lower quality sheets. In the 1840s, a method was developed for using ground wood pulp in the paper making process. This type of pulp contains lignin which is acidic and darkens on exposure to light.

The use of new materials, such as recycled fibres, optical brighteners and colourants and new manufacturing processes from the 1980s onwards has increased the types of paper available. However these processes and material all have an effect of the longevity of the paper and a paper conservator must be aware of the methods of production to successfully treat objects made from modern paper.

Manufacturing process

Early papermaking was all carried out by hand, which resulted in a good quality strong sheet. However, it was a long and laborious process and many sought to mechanise the manufacturing procedure to increase production.

The first papermaking machine was invented in 1798 by Nicholas-Louis Robert. This mechanical pulping and formation resulted in shorter fibres and also unintentionally introduced metallic particles into the paper resulting in a weaker sheet.

Chemical pulping was introduced in 1854 by Hugh Burgers and Charles Watt. Chemical pulping removes lignin and does not cut up the fibres as much as mechanical pulping, resulting in a stronger paper.

From the mid-1970s thermomechanical pulping was widely used. This method uses heat and mechanical pulping to soften the wood chips used in paper making. Today, the sulphate process is most commonly used to produce paper. This is a chemical procedure in which wood chips are treated with sulphurous acid under high pressure to produce cellulose and extract lignin.

Alum rosin sizing was introduced in the early 18th century in attempt to strengthen the paper; however, this sizing caused further acid to be formed within the paper. Wood pulp paper from before the 1980s also tends to be acidic from the alum-rosin sizing used. However, the development of a synthetic sizing in the 1980s has enabled the production of a paper with a neutral to slightly alkaline pH. This combined with a calcium carbonate filler which acts as an alkaline reserve to prevent acid contamination from the environment has resulted in a paper with better aging characteristics than modern papers from the earlier 20th century.

This website by the National Archive of Australia gives a good overview of the paper making process and how it has changed over time: http://paper.naa.gov.au/chronology/

External causes of paper deterioration

Environmental conditions

Temperature: high temperatures increase chemical reactions. An increase of 10 degrees C doubles the reaction rate. Therefore, a cooler environment is preferred for paper collections.

Humidity: moisture in the air can also accelerate chemical reactions. High levels of humidity can aid mould growth and encourage pests. Equally, low levels can cause desiccation of the object and result in increased brittleness.

Fluctuation of these conditions causes the material to expand and contract. Over a long period of time this can weaken the physical bonds within the paper and cause loss of strength.

Pollutants

Gaseous pollutants can originate externally from industrial and vehicle fumes, or internally from common materials such as paint, plastics, cleaning supplies, and photocopiers. These pollutants, especially when combined with a humid atmosphere, can initiate chemical reactions that can result in paper degradation.

Light

The absorption of energy from light can trigger chemical reactions that degrade paper. UV light is particularly damaging as it has more energy than other longer wavelengths of light. Light can cause the lignin in paper to darken and cause inks and dyes to fade. Other forms of light such as direct sunlight and infra-red bulbs can also produce heat which again causes paper to degrade.

Handling and storage

In the HIV/AIDS collection, the majority of the damage to the paper documents is due to poor handling and storage during use, prior to accession. They were often used in offices and as such not handled with great care as they were just seen as ephemeral documents.

Paperclips and staples

Frequently metallic paper clips or staples are used to hold loose sheets together; however, these can rust over time and cause planar distortion of the paper. These damaged areas now represent an area of weakness, which will be more susceptible to damage over time.


A rusted paper clip and staple on two sheets of paper	Planar distortion of paper caused by metallic fasteners

Creasing

Due to inappropriate storage and careless handling, papers can easily become creased. These creases weaken the paper fibres and may be more likely to tear in the future. This is often cause by inappropriate storage. For example, documents placed in a ring binder may exhibit tearing around the hole punches.


Sheet of creased paper	Sheet of creased paper

Tears

This is often caused by inappropriate storage. For example, documents placed in a ring binder may exhibit tearing around the punched holes.


An example of a torn piece of paper from GD24	An area of loss in a sheet of paper

Surface Dirt

Although it may seem innocuous, surface dirt can absorb pollutants from the atmosphere. These can then migrate into paper and increase the acidity of the paper. Surface dirt can also provide a food source for pests and encourage mould growth. Without appropriate storage, dirt can accumulate on the paper surface and result in paper degradation.