Before my mom got married she worked at Kaiser Steel in Fontana as a secretary, where she did a lot of typing of letters, memos, and forms. The method of correcting errors at the time was to use a razorblade to scrape the ink off the page.
Bette Nesmith, mother of Mike Nesmith (of the band The Monkees), was also a secretary and typist around the same time. Frustrated by the razorblade method, she would touch up her mistakes with a fast drying white paint that she concocted at home. The correction paint, which she named 'Mistake Out', became popular, and she started selling it in little bottles. Eventually Gillette bought her business for $47 million dollars.