From a day when most people simply sharpened their edge tools, rather than bought disposable ones. I like to pick then up when I find them and put them back to use. Below, a 1950's flyer with helpful information for homeowners on the various types of abrasive stones.
For those who really want the low-down on creating a keen edge, you can't do better than to read Leonard Lee's 1995 book, The Complete Guide to Sharpening. (Leonard Lee founded Lee Valley Tools, so you can certainly trust his expertise.)