One of the declassified documents outlines the chemicals and techniques necessary for developing certain types of secret writing ink and a method for opening sealed letters without detection.
Notes on verification
Multiple independent outlets (Reuters, The Guardian, NBC) corroborate the CIA's 2011 declassification announcement describing secret ink formulas and covert letter-opening techniques from WWI-era documents. [tier=silver indep_score=0.7 clusters=3 claim_tier=notable | framework convergence=partial on CIA's 2011 declassification announcement of its two oldest classified documents (upstreams: CIA (Central Intelligence Agency) 2011 declassification release) — publishers independent, evidence may not be | kind=attributed eligibility=medium]
Sources
- Secret Writing: CIA's Oldest Classified Documents - CIA (seed:conspiracy_and_investigation)
- https://www.reuters.com/article/us-usa-cia-documents/cia-declassifies-oldest-documents-containing-secret-ink-formulas-idUSTRE73D8H020110415 (corroboration)
- https://www.theguardian.com/world/2011/apr/17/cia-declassifies-oldest-documents-secret-ink (corroboration)
- https://www.nbcnews.com/id/wbna42630961 (corroboration)