The New York Academy of Medicine has an extensive collection of material related to medical advertising, including a set of Beecham's "Oracle" Cards. The paper cards, approximately 13cm x 19cm, printed by the Beecham Pill Company (St. Helen's, Lancashire, England) in the 1890s, contain "secret" messages written in potassium nitrate on a blank background. The holder of the card is invited to "apply a RED-HOT Wire, Pin, or Needle" to a designated mark on the paper in order to ignite the potassium nitrate and reveal the hidden message burned into the paper.
All the cards in the collection have been activated, except for one. From what I have been able to determine, potassium nitrate is not combustible in the same way as cellulose nitrate, for example, but it will enhance the combustion of other materials. Has anyone else dealt with potassium nitrate in collections? Do you have recommendations for the best way to store this card? Would storing it in a well ventilated, climate controlled vault maintained at 65F and 45%RH be acceptable or should we consider cold storage options? SCOTT W. DEVINE Head of Preservation Gladys Brooks Book and Paper Conservation Laboratory 212.822.7365 The New York Academy of Medicine LIBRARY 1216 Fifth Avenue | New York, NY 10029 ****** Unsubscribe by sending a message to [email protected] Archives through August 2016 at http://cool.conservation-us.org/byform/mailing-lists/cdl/ Archives from September 2016 onward at https://www.mail-archive.com/[email protected]/
