Why acid-free products?

In our day-to-day dealings with customers, we often hear these questions: What exactly is an acid-free storage product? Do books and documents really need to be stored in special boxes or folders? Isn’t it enough to use ordinary ring-binders and folders, available in each stationery?

The answer is: no, ordinary storage products are not sufficient if we wish to preserve a document, a book or a photo in good state for longer than several years. Ordinary boxes, ring-binders and folders offered in stationery shops are mostly used to keep documents in order and well organized. However, they are not suitable for long-term storage and preservation since the boards they are made of might be acidic or might contain harmful components, such as brightening agents. Such products will not protect documents against degradation but they will accelerate it. 

How is this possible? Unfortunately, this is the nature of paper; cellulose fibres, the main component of paper, disintegrate when exposed to acids. Most of us have had an experience of holding a book or a newspaper issued a few decades ago whose pages turned yellow or even brown and became extremely brittle. It happens mostly because of acids e.g. sulphur and nitrogen compounds present in polluted air. The biggest problem, however, is that paper itself contains acidic components. It is not without reason that the paper produced between the mid 19th century and the end of the 20th century is called „Suicide-Paper”. As printing in that period was becoming widespread on an unprecedented scale, paper industry searched for cheaper and more efficient methods of paper production. In consequence, they started mixing cellulose with wood pulp, brightening agents or glues and thus caused its acidification and, eventually, disintegration. We need to realize that it is the world's cultural heritage that falls apart as a result of disintegration of cellulose fibres. Various unique works of art and literature, documents which changed the history - all these testimonies of the past slowly turn into dust, just as the newspaper from a few decades ago.

This issue has been troubling archivists, librarians and scientists for many years. Some methods of de-acidification have been discovered but they remain very expensive, so only the biggest libraries and archives can afford them, and only the most valuable collections undergo these treatments. Appropriate storage of paper plays a major role in this context. There are some inevitable harmful factors, such as polluted environment or some components of paper, so the aim is to add some elements which can slow down the deterioration process of paper instead of accelerating it. It is worth noting that acids can migrate from one object to another or from a storage product to its contents. If we have a book made of highest quality paper (pure cellulose with no brightening agents or wood pulp), which is resistant to the process of disintegration, and we store it in a box made of acidic board, it will gradually acidify the book and destroy it. That is why using acid-free storage products is so important. Such products will not accelerate the disintegration of cellulose fibres; instead they will create an optimal and safe environment for the stored objects and separate them from harmful impact of external factors.

What criteria should be met by storage products intended for archival storage?

Storage products meant for long-term storage of books and documents should be made of materials with the following parameters:

  • pH between 7.5 and 10;
  • alkaline reserve > 0.4 mol/kg (in case of calcium carbonate, paper should contain at least 2% of CaCO3)
  • Kappa number < 5, which means 100% cellulose (especially regarding file covers)

What does it mean? The pH value informs us about the (non-)acidity of a given storage product. pH scale is a quantitative scale used to specify the acidity or alkalinity of an aqueous solutions, its values range from 0 to 14. The pH value of 7 means that a solution is neutral, e.g. distilled water. Solutions with pH lower than 7 are acidic – storage products made of materials with such pH accelerate the process of deterioration of archived materials. That is why, when choosing the right storage product, we should make sure that it's made of a material with pH value between 7.5 and 10. We should also bear in mind that this requirement applies to all layers of board. 

Alkaline reserve means that board or paper have been produced with addition of a basic component (usually calcium carbonate), which will neutralize acidic compounds, including those appearing at a later time. This way it will ensure efficient protection of the stored object for a longer time. 

The Kappa number is a parameter specifying the maximum content of oxidizing agents in paper and board. Its value should be lower than 5, a requirement which can only be met by board made of ~100% pure cellulose and no wood pulp.

We should also emphasize that storage products meant for storage of valuable collections ought to be characterized by high mechanical resistance. That is why most of our storage products are made of solid board, which, compared to corrugated board, is much more durable, rigid and resistant to soaking. 

The highest quality of products for long-term storage of paper is certified by International Standards ISO 9706:1994 and ISO 16245:2009. 

Beskid Plus Company offers a wide variety of storage products made of acid-free board and paper, suitable for the long-term storage of records. You can find detailed characteristics of our materials used for production of our boxes and folders in the Paper & Board section. Should you have any questions or problems with choosing the right material, please contact our employees, who are well qualified and more than happy to help you find the best solution.

Prepared by: Zofia Parchańska-Puczek

Bogacz-Walska, Monika, 1998, Główne przyczyny niszczenia materiałów archiwalnych, [w:] Archeion, T. XCIX, Warszawa
Hebig, Dieter, 2001, Schutzverpackungen – ein wichtiger Beitrag zur Bestanderhaltung von Archiv- und Bibliotheksgut, [w:] INFO 7, Heft 3, s. 143-150