Tuesday, November 27, 2012

What is Archival Paper?

A woodcut of a papermaker
Many artists talk about working to archival standards.  But what is archival paper for artists?

This post is a review of
  • what causes paper to deteriorate
  • what is classed as archival paper - and what archival paper means for artists; 
  • how to acquire and maintain good quality fine art paper over time
What happens to paper over time?

Paper can deteriorate over time unless:
  • the production process eliminates matter which causes it to change
  • storage and handling sustain the quality of the original paper over time
You've probably all seen how newsprint discolours and becomes very brittle over time and crumbles if exposed to air and/or sunlight.

Other papers also deteriorate as well. For example, many of the pastel artworks by master pastellists in museums are shown in low lights. This is NOT because of the quality of the pigment in the pastels (although some may well be fugitive) so much as the fragility of the paper or ground used when the artwork was produced.  Similarly we can see watercolours in museum exhibitions where the paint is fine and the paper is in a less than pristine condition.

If you want your artwork to survive over time it's necessary to ensure that it's produced on paper which will not deteriorate over time.  However that's easier said than done.

So why does paper deteriorate?  Below are a list of things which affect the quality and condition of paper over time.

Things which are bad for paper quality and condition over time

  • Chemical composition:
    • short cells are more unstable
    • lignin - this is the part of woody plant fibres which cause paper to degrade.  It's an acidic organic polymer which causes paper made from wood pulp to yelllow and its mechanical strength to weaken.  Wood is chemically pulped in order to separate lignin from cellulose.
the British Trade Standard definition for the paper trade of an uncoated woodfree and acid free paper can include 10% Thermo-Chemi-Mechanical Pulp and 1% lignin, it is clear that British Standards are not always what one might expect. The lignin produces acids as it degrades, thereby introducing a destructive force into the paper.RK Burt - How long is long life?
    • wooden drawers which contain lignin!  (In order to prevent the migration of acid from wood to paper these need to be lined with acid free paper or boards)
    • traces of bleaching left in/on the paper will cause paper to become yellow and brittle
    • optical brightening agents can produce a brighter whiter sheet of paper - but this can change over time and the sheet may well yellow over time. 
  • Light: discolouration following exposure to sunlight (ie ultraviolet (UV) radiation) and/or high lighting levels
  • Humidity:  Mould spores can cover paper if allowed to grow because the atmosphere is too humid (ie 60%+)
  • Temperature: high temperatures incerease deterioration
  • Pest attack: - they can spoil, tear and/or eat paper! 
Rats, mice, silverfish and cockroaches are the most common problems but termites, birds and possums may also be encountered. Moths, ants and spiders are not likely to damage a paper collection but may attract other pests that do.National Archives of Australia - Integrated Pest Management
  • Time: All material deteriorates over time. The issue is how long does it take and what impact does it have over a specified period of time.
What does archival paper mean?

Paper and other supports which are intended to last a long time can be variously described - such as
  • "Conservation-grade" (acid-free, buffered paper made from wood-based pulp) or 
  • Archival-grade (aka Museum-grade ie cotton rag paper made from cotton pulp).
Archival quality can mean:
  • the standards laid down by Museums - which tends to be very high and relates to centuries.  (See the National Archives of Australia documentation for a 'plain English' guide to archival matters). However if you want to work to a high but not the highest standard then there are things you need to know.
  • the standards laid down by the International Standards.  However you need to read the small print
    • permanent" paper is ISO 9706 - however this standard does NOT require tests that ensure a fine art paper will retain the optical properties expected of such paper eg brightness.  That's because it's designed for uses other than fine art.
How long is long life? The British standard ISO 9706 may be an inadequate benchmark for the Fine Art market where expectations will probably exceed the "Statute of Limitations" (6 years).R. K. Burt
    • "archival" paper, the standard is ISO 11108 - stipulates requirements for permanence and durability of documents and publications required for permanent retention and frequent use.
It's important to recognise that papers satisfying ISO 9706 are using a standard which was not designed for fine art.  Hence a PH neutral / acid free paper might NOT achieve the standard required for an artwork which should have a life in decades.

In my opinion, on the whole if you want to your artwork to be preserved over time, it's probably safer to go with papers which are made from cotton rag or linen.  

The Australian National Archives have a very useful statement about archival paper for artwork 'Choosing the right paper'.

Standards Australia have also very sensibly developed a watermark for papers which satisfy their requirements for both chemical and physical stability and quality over time.

How to ensure good quality paper condition over time

How fine art paper behaves depends on what was used to make it and how it is used and stored. 

Below are some suggestions - culled from various reference sources (see end) as to factors which help to promote the longevity and good condition of fine art paper.

Things which improve physical and chemical stability

Archival stability is a function of chemical and physical stability.
  • Chemical composition - chemically PH Neutral
    • the removal of all lignin and any other chemicals which are acidic or destructive
    • buffering to prevent the formation of any additional acids
    • all fillers and sizing additives must also be acid-free
  • Physical composition: long cells - more stable over time.  These are present in:
    • cotton (ie natural cellulose) or linen rags
    • 100% cellulose extracted from wood pulp
How paper is stored and handled makes a huge difference to quality and condition over time.
  • Storage:
    • Watercolours, drawings, prints and posters should be stored flat.
    • store in containers which maintain acid-free surfaces all around the paper
    • store away from UV light and any high levels of  artificial lighting
    • store in an atmosphere which is not too dry and not too damp.  The target humidity range should be between 45-50%, but above 30% and below 60% is acceptable.  Keep humidity fluctuations to a minimum
    • ideally store at temperatures between 18 and 20°C
    • prevent pest attack (National Archives of Australia has a very helpful document about pest management)
    • Interleave finished artwork with acid-free paper to prevent transfers between artworks
    • use archival boxes for small artworks
    • plastic storage must be free of plasticisers, surface coatings and other harmful chemicals (ie 
  • Minimise handling: Use clear labelling so that you only handle what you need to handle
Matting paper-based artwork

It's imperative that all surfaces which come into contact with a paper also achieve the same grade of permanence.
  • Use PH neutral / acid free mats as a minimum - however note that ISO 9706 permits the inclusion of lignin and does not require paper to stay bright over time
  • Ideally use museum grade mats
  • ensure backing boards are also acid free and PH neutral.
References:

Here are some reference sources which I'm adding to a website about archival paper:

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