Effects of acidic vapors on a freshwater clam shell is clearly visible in white on this specimen. The shell was deliberately exposed to an excessively humid and acidic medium of acetic acid for sveral weeks. The dark areas are a normal variant to the shell of this bivalve.
Unfortunately, space constraints kept me from finishing my discussion of Byne’s Disease in last month’s column.
You will remember that Byne’s Disease is a white efflorescence resembling salt (see images) that can be found on shell objects (e.g., California clamshell money, wampum or cowrie shells) stored in an acidic environment.
My recommendation is to avoid this condition by storing these items in a safe environment similar to those recommended for the storage of other numismatic materials (i.e., archival quality, acid and lignin-free).
In addition to being acid-free, the storage container should also suit the size and weight of the shell.
Small polyethylene bags would suit a cowrie shell quite well, while larger clam shells should be stored in a box that can provide them with adequate support and protection.
If you have wampum in your collection, you might need to construct a custom storage mount to properly support the object in the storage box. Archival suppliers offer a wide variety of storage boxes.
Readers interested in learning more about Byne’s Disease are directed to two online resources: (1) the National Park Service Conserve O Gram “Byne’s ‘Disease’: How to Recognize, Handle and Store Affected Shells and Related Collections” (Number 11/15, August 2008) written by Sally Shelton, conservator of natural history collections (www.nps.gov/museum/publications/conserveogram/11-15.pdf), and (2) Conchologists of America (www.conchologistsofamerica.org/articles/y2002/0209_callomon.asp), “Byne’s Disease — Questions and Answers” written by Paul Callomon, Collections Manager, Department of Malacology, Academy of Natural Sciences, Philadelphia.
For those looking for a more technical source, there’s the scholarly article “The Deterioration of Mollusca Collections: Identification of Efflorescence” written by Norman Tennent and Thomas Baird, published in Studies in Conservation, Volume 30 (2), 1985: 73-85 (www.jstor.org/action/show
Publisher?publisherCode=iich) (access to this article is limited to subscribing institutions).
Acid-free boxes and tissue are available from archival houses such as: Carr McLean (online at www.carrmclean.ca), Gaylord Brothers (www.gaylord.com) or University Products Inc. (www.universityproducts.com).
Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.