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Acidity
The longevity of books is threatened by the enormous problem of acidic paper.
A volume containing browned and brittle paper due to the effects of acidity is a very common sight. This occurs mainly in paper produced from wood pulp due to its high levels of lignin – an acidic and unstable element found in many plants.
- Acidic volume
Paper Contents
Before the 1850s, cotton was the main constituent of paper (rag paper). Cotton contains a very low level of lignin, which means that paper produced before this date remains in a comparatively good and stable condition. Unfortunately, it wasn’t possible to produce enough rag paper to keep up with the massive increase in demand caused by the growth in literacy and the publication of more and more books during the 19th century. To fulfil this demand, paper was successfully produced from wood pulp on a large scale from the 1850s onwards. Because of this, a high percentage of books published from that time onwards contain a high level of lignin, an acidic and unstable element, resulting in the browned and brittle paper that we see today in many books.
- Effect of acidity
Guidelines to lessen the effects of acidity
Acidic paper can be treated, and this does take place on a small scale at the Conservation Treatment Unit, but it’s an expensive process. The best way to deal with fragile books is to handle them with great care and ensure that they are kept under the correct environmental conditions (see Temperature and Humidity). This will not get rid of the acidity, but a stable environment should slow down the chemical degradation.
We should also be aware of the effects of acidic gases (peroxides) that are released from wood and from modern building materials such as plywood and chipboard etc. A document kept on unsealed wood can become stained and brittle over a period of time. Such wood should be sealed with a polyurethane varnish.
