Preserve against degradation
This is the second part in a multipart review of the manufacture, degradation and preservation of paper money.
Rag note paper is a good quality paper that begins life pure and acid-free. The main component of the linen and cotton in rag paper is cellulose.
Cellulose is a long, chain-like, glucose polymer. Cellulose has two major enemies — light and acids. Both cause the cellulose to be degraded or broken down. As a cellulose polymer degrades, its long chains are broken into smaller units. The shorter the cellulose chain gets, the weaker the paper becomes.
It is the breakdown of the cellulose molecules that makes old degraded paper brittle and friable.
Ground-wood paper tends to be of poor quality with little long-term strength and durability. This is due in part to the pulping method, which produces extremely short paper fibers. Shorter fibers mean weaker paper.
Wood-based paper also has large amounts of lignin. Lignin is found in all vascular plants, including trees.
Lignin is the binding material that holds the wood fibers together in the tree giving it the strength it needs to grow tall. Lignin is the fiber in your food. The chemistry of lignin is quite complicated. Many lignins exist, all of them complex three-dimensional polymers.
What we need to know is that lignin in paper will ultimately break down, causing the paper to become acidic and degrade. The cellulose in ground-wood paper degrades in the same fashion as that in rag paper, but is accelerated by the presence of acidic impurities and by lignin.
Even if it begins life white and strong, ground-wood paper quickly turns brown due to acidic degradation products and eventually crumbles away. Notes printed on ground-wood paper will be inherently unstable and more susceptible to degradation.
Preserving paper-based materials is fairly straightforward if you keep in mind paper’s inherent weaknesses and protect it from the elements that cause it to degrade. We know that paper tears, creases and soils easily. With this in mind, it is important that you understand how to handle your collection of paper money properly.
Paper soils easily because it is absorbent. Minimize your contact with the note by storing it flat in a safe archival-quality holder.
Polyethylene, polypropylene and polyester (i.e., polyethylene terephthalate) are all considered safe materials. Regular readers will remember that Mylar D, a brand name version of polyethylene terephthalate, was once an industry standard but is no longer available from the manufacturer. A substitute of the same compilation has been found. It is referred to in the archival catalogs simply as “polyester.”
I prefer storing numismatic materials in see-through holders rather than paper envelopes because you do not have to remove the item from the holder to examine it. If you do choose paper envelopes, make sure they are acid-free and lignin-free.
Acid- and lignin-free paper folders are suitable for oversize notes and uncut sheets of currency.
When handling notes, your hands should be clean and dry. Remove any sharp rings or jewelry that could catch on the paper.
Wash and dry your hands regularly if handling a large number of notes. Notes that have been in circulation can be very dirty. Given how absorbent paper is, avoid smoking, eating and drinking while handling collections.
Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.