What’s the difference between Acid-Free and Archival?
Acid-free papers are made using alkaline papermaking technology. This means the pH of the pulp that is used to form the paper is above 7 (neutral). Typically papers will be buffered with an alkaline reserve, such as calcium carbonate (chalk) to neutralize acid compounds absorbed from the atmosphere or formed through natural aging.
There are no universal standards in regards to what makes a paper “archival” but there are some generally accepted properties. In addition to being acid free, the paper should contain no groundwood or unbleached pulp, and be free of optical brighteners.
Many papers and materials will also undergo a series of testing and certifications to determine their longevity and quality.
The Photographic Activity Test (PAT test, NSI IT 9.16 / ISO 14523-1999) is an accelerated test that predicts the effects a material may have on photographic images.
Papers that meet the ISO 9706: Permanency requirements for paper is another valuable test which specifies the requirements for permanent paper intended for documents given in terms of minimum strength measured by a tear test, minimum content of substance (such as calcium carbonate) that that neutralize acid action measured by the alkali reserve, maximum content of easily oxidized material measured by the kappa number, maximum and minimum pH values of a cold water extract of the paper.
The ANSI / NISO Z.39.48-1992 Permanence of paper in Library and Archives is another Certification that materials can undergo to determine their permanence.
If you are looking for the ultimate in permanence, we recommend acid free surfaces made with 100% cotton and the above certifications.
What other factors make paper acidic or speed up the process?
UV light and heat will speed up the chemical process that causes the degradation of paper. You’ll see this on the edges of the pages of a book that have been on a bookshelf exposed to light.
Other than the paper itself being a source of acidity, there are other sources that introduce acid to papers, called “migrant acidity”. Migrant acidity comes from the environment the paper is in, this could be something very acidic such as an old degraded PVC pocket, another sheet of acidic paper or board, or even airborne pollution.