US Coins

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Slide storage box, above, acquired by a collector, has a baked enamel finish. Another archival storage box option, right, is from University Products in Holyoke, Mass.

Steel case image, top, courtesy of author; archival box image, below, courtesy of University Products.

Not long ago a reader emailed me asking the following:

“I recently purchased some slide storage boxes at an auction. They are steel and have a plastic insert that holds 150 2x2 photographic slides. I am wondering if they would be safe for coin storage?”

Very good question. It is important to consider all of the components of the box when assessing whether or not they are suitable for storing one’s collection.

The slide boxes, illustrated above, are indeed made of steel and have a baked enamel finish.

Steel with a baked enamel finish is considered safe for storing numismatic collections, provided the enamel finish was properly cured.

If a baked enamel finish is not properly cured, it will off-gas formaldehyde and other volatiles that can harm collections.

A simple spot test — the MEK rub test — can be used to test if a baked enamel coating is properly cured.

MEK, short for methyl ethyl ketone, will dissolve an improperly cured enamel coating. To carry out the MEK rub test, dip a small swab in the solvent and rub it over the surface of the coating. If the coating is properly cured, the solvent will not dissolve the coating.

Carry out the test in an area with good ventilation, preferably in a fume hood.

Thankfully, I have never heard of a finish on these slide boxes being problematic.

The plastic inserts are polystyrene. Regular readers will remember that polystyrene is considered safe for storing numismatic collections.

The one component of these boxes that I am concerned about is the paper that is adhered to the inside of the lid.

If the paper is acid and lignin-free then it is safe. If not, it should be removed.

Testing for pH and the presence of lignin is fairly straightforward, covered in my Nov. 22, 2010, and Oct. 25, 2010, installments, respectively, of this column.

Slide storage boxes such as the ones the reader bought are still available from archival supply houses. Both Carr McLean ( and Gaylord ( carry them.

Archival slide storage boxes, illustrated above, are available for purchase from Carr McLean, Gaylord and University Products ( and are another option.

Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.

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