“Acid-free” and “archival” are terms that come up fairly often when art is the subject matter of a conversation. Now, what do these terms really mean, and how does something become “acid-free”? This will depend on the materials in question.
This print shows a fair amount of acidic damage, most likely caused by inappropriate matting.
Source: Heritage Auctions.
When it comes to paper, what we refer to as “acid” is actually hydrochloric acid, an inorganic chemical system. This chemical comes about from the bleach (used to make the paper white) reacting with lignin (a naturally occurring compound in wood) as the paper ages. Hydrochloric acid is classified as “strongly acidic,” thus it will begin to break down the paper’s chemical components and cause the yellowing most commonly associated with old documents, art, and newspaper.
This conversation does not end there, however. Even with archival paper, there is the potential of other materials coming into contact with the art and transferring hydrochloric acid, therefore still compromising its longevity. These materials can vary from matting and backing, to adhesive and glues. Anything that comes into direct contact with portion of the artwork has the potential to cause damage and accelerate the artwork’s deterioration.
Damage details.
Source: Heritage Auctions.
In terms of ink, the conversation takes a different turn. While the longest lasting inks will still be those that are relatively pH neutral (not acidic, nor basic), there are other factors that greatly affect longevity. The most important being whether the ink is dye or pigment based. Generally speaking, dye based inks will have a significantly shorter lifespan than pigmented inks. However, this is not to say that pigment based inks are always superior. Both types are available as archival inks, and each one has their own drawbacks and advantages. Assessing how important factors such as brightness, and color gamut are for a project, can help one decide whether pigments or dyes are most appropriate. Just remember, “if it’s art, it better be archival.”