Page "Invisible ink" Paragraph 68
from
Wikipedia
As an indication of security, most inks mentioned above were already known by the end of World War I.
However, in 1999, the U. S. Central Intelligence Agency successfully requested that a 1940s technical report on invisible ink remained exempt from mandatory declassification, based on the claim that invisible ink was still relevant to national security.
Page 1 of 1.
1.936 seconds.