The Rich History Of A Centuries-old Document Security Technologyfolding And Securing A Letter Into Its Own Envelope For Deliveryand A Comprehensive Guide To Learning How To Make Your Own Locked Letters.before The Invention Of The Gummed Envelope In The 1830s, How Did People Secure Their Private Letters? The Answer Is Letterlockingthe Ingenious Process Of Securing A Letter Using A Combination Of Folds, Tucks, Slits, Or Adhesives Such As Sealing Wax, So That It Becomes Its Own Envelope. This Almost Entirely Forgotten Practice, Used By Historical Figures Ranging From Elizabeth I And Her Spies To Japanese Samurai Lords, Was An Everyday Activity For Centuries, Across Cultures, Borders, And Social Classes.