In this week’s blog, our project conservator Emily looks at the processes and materials used to create modern papers.
I have recently started working with one part of the HIV/AIDS collection that is mainly made up of loose paper documents from the late 80s and early 90s. There is a huge diversity of papers found in the collection, from glossy papers used for flyers to regular office notepad paper, folders made from thick card to faxes made from shiny lightweight paper. As a conservator, I wanted to find out more about how papers formed in the past 50 years are made and how they might deteriorate in the future.
|A selection of papers found in GD22, before treatment.|
|A newspaper from GD22/10. The paper has become brittle and the edges have discoloured.|
Papers made from the late 1970s onwards are mostly formed from wood chips that have been softened using steam and pulped mechanically in a process called thermomechanical pulping. Since the chips are firstly softened, less energy is required than the previous solely mechanical method and less damage to the fibres is caused, resulting in a stronger sheet. This method also allows for chemicals to be added to the pulp to improve the sheet. For example, calcium carbonate can be added as a filler. This acts as an alkaline buffer against the formation of damaging acids within the sheet.
This method improved the quality of the sheet, but still does not remove the lignin. Today, most paper is created using the sulphate process. This was first used in the 1930s and involves treating the wood pulp with a mixture of sodium hydroxide and sodium sulphide to extract the lignin. This method produces a strong, less acidic sheet. Paper made with this process will age better than previous modern papers.
The characteristics of paper can also be changed using additives. For example, bleaches and optical brighteners can be used to lighten the paper and colourants or dyes are used to change the paper colour. Different finishing processes and coatings can also be used to change the surface texture of the sheet. For example, paper sheets can be glazed to make them super glossy for use in magazines or left uncoated to be used as stationary.
|A collection of differently coloured office papers found in GD24.|
For more information on the deterioration of modern paper found in the HIV/AIDS collections and treatment of it, please see the project home page on the LHSA website: http://www.lhsa.lib.ed.ac.uk/projects/UNESCOcollections.htm
A useful chronology of paper making technology and materials can be found at the National Archives of Australia website http://paper.naa.gov.au/chronology/
Emily HickProject Conservator