Claim: Security paper was produced by using a soluble thiocyanate and lead and was granted an initial patent in the early 20th century.
Evidence: According to the patent, the method by which security paper was produced involved using a soluble thiocyanate (such as ammonium thiocyanate) and lead, which could be used to create an insoluble salt, lead thiocyanate. An initial patent for the manufacturing process for security paper was granted to Robert E. Menzies and John E. Aitken in the early 20th century.