Buffered or unbuffered? Choosing conservation papers and boards
When choosing boxes, folders, envelopes or interleaving for a collection, "acid free" is usually one of the first things people look for. It is a sensible starting point: acidic housing materials can contribute to the deterioration of the objects they are meant to protect. But acid free on its own does not tell the whole story. Conservation papers and boards are commonly available in two main types, buffered and unbuffered, and for some materials the difference matters.
What "buffered" means
Buffered papers and boards contain an alkaline reserve, usually calcium carbonate, added during manufacture. This reserve can help neutralise acids that come into contact with the housing material over time, providing additional protection against acidic substances associated with objects or their surroundings.
Buffered housing is commonly used for many paper based materials, such as documents, books, maps and prints, especially where the paper itself is acidic. Many papers made from wood pulp during the nineteenth and twentieth centuries fall into this group.
However, buffered materials are not necessarily appropriate for every object containing paper, particularly when other materials or components may be sensitive to alkaline conditions.
What "unbuffered" means
Unbuffered papers and boards contain no deliberately added alkaline reserve. They are generally manufactured to have a neutral or near neutral pH and are often considered for materials that may be sensitive to alkaline conditions.
Examples include certain photographic processes and some protein based materials, such as silk, wool, leather and parchment. However, their suitability should be assessed according to the characteristics and condition of each object, rather than assuming that unbuffered materials are always preferable.
Photographic materials require particular attention. Both buffered and unbuffered enclosures may be appropriate depending on the photographic process. Storage materials intended for direct contact with photographs should meet relevant photographic preservation requirements, including the Photographic Activity Test (PAT), specified in ISO 18916.
Why there is no single answer
It would be convenient to have one box for everything, but collections are rarely that simple. A single archive file can contain letters on acidic paper, a photograph and a fabric sample. A museum store can hold paper, textiles and composite objects side by side.
The right housing depends on what each object is made of, its condition, how it is used and how and where it will be stored. Mixed collections may need more than one solution and, in some cases, additional separation or barrier materials. Any barrier material should itself be compatible with the objects concerned and suitable for the intended storage conditions.
It is also worth remembering that housing is one part of preventive conservation, not the whole of it. A well chosen box contributes to protecting an object, but the storage environment, handling practices and regular monitoring remain equally important.
A few questions to ask
Before choosing between buffered and unbuffered materials, it helps to consider:
- What is the object made of, and does it combine different materials?
- Is the material known or likely to be acidic?
- Does it include photographic processes or components potentially sensitive to alkaline conditions?
- Will the housing material be in direct contact with the object?
- Is there specific guidance from your institution or a conservator for this type of object?
These considerations can help identify suitable housing options while avoiding unnecessary generalisations.
How EXPM can help
EXPM supplies conservation housing materials for archives, libraries and museums through expmstore.com, and our team works with institutions on preventive conservation and storage projects.
If you are unsure which option suits your collection, visit expm.com.pt or contact our team to discuss it.
Keeping History Alive.