US Coins

Tips on preserving your collection: Maltby

By Susan L. Maltby

Published: May 14, 2016, 4 PM

This image shows how one collector is storing his coins that have been graded and encapsulated by a third-party grading service. Called a Hollinger box, it has acid-free and lignin-free dividers made from Talas Heritage Corrugated Board.

Image courtesy of Susan L. Maltby.

Preserving Collectibles column from May 30, 2016, Weekly issue of Coin World:

A recent reader expressed concern about using “buffered” archival tissue and boxes for storing his coin collection.

Conservators regularly recommend that collections be stored in “archival quality” enclosures. This means materials are safe and will not cause your collection harm.

Archival-quality paper, tissue and matboard should be acid- and lignin-free. Archival-quality paper comes from two main sources: rags and purified wood pulp.

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The best quality is rag paper. This paper is made from either cotton or linen rags and is the purest. It is also the most expensive paper available. Good quality stationery often contains some rag paper.

Paper made from purified wood pulp has been chemically treated to remove lignin. Lignin is present in all vascular plants. It is the binding material that holds the wood fibers together in a tree giving it the strength to stand up and grow tall. Lignin is the roughage in your food.

Lignin breaks down easily to form acidic compounds, which in turn attack the cellulose in the paper and cause it to degrade. The presence of lignin in paper automatically makes it nonarchival. Chemically treating wood pulp dissolves and washes away the lignin. Archival-quality paper that is marked “acid- and lignin-free” is made from chemically purified wood pulp.

The majority of the paper-based archival products are labeled “buffered.” Buffered paper has had an alkaline material — calcium carbonate — added to protect the paper against acids that occur either in the environment or coming from the object itself. The buffering agent acts like an antacid tablet, neutralizing acids in the vicinity of the object. Archival-quality paper should contain no more than 3 percent buffering agent. A pH of 8.5 is standard for archival-quality buffered materials.

The pH of a material refers to whether it is acidic, basic or neutral. The pH scale is logarithmic and ranges from 0 to 14 with 7 as neutral. Values below pH 7 are acidic and values above are basic or alkaline. The farther one goes from the neutral point of 7, the greater the level of acidity or alkalinity.

It is common knowledge that acids corrode metals. As such, we strive to keep them in an acid-free environment. Amphoteric metals (e.g., aluminum, tin, zinc and lead) are sensitive to both acidic and alkaline environments. Their sensitivity lies in the fact that their corrosion products dissolve in both acidic and alkaline solutions, accelerating the rate of corrosion.

The pH of the solutions needed to cause this solubility varies with each metal. For example, a solution with a pH below 6 or above 12 is needed to dissolve the oxide layer for zinc, whereas for aluminum, the pH of the solution needs to be below pH 4 or above pH 9.

So, is buffered acid-free tissue and boxes an issue with these metals? In my opinion, no. It would only be a problem if they got wet.

Water is needed to make the solution that would dissolve the corrosion products. If the risk of flooding and severe weather is high, collectors may wish to consider choosing Coroplast boxes over those made from acid- and lignin-free board.

Coroplast is a copolymer of polypropylene and polyethylene. It is considered safe for storing collections and has the added advantage of being waterproof.