Honing film is the least expensive way to get started with a sharpening system. For very few dollars you can have an enormous range of grit sizes, a flat thing or two to stick the film to (glass, granite, etc.) and you’re ready to sharpen all the way to 0.3µ (that’s the Greek letter “mu” that stands for micron, one of which is one millionth of a meter) if you so desire. (By the way, that’s a very small particle. We’re talking 0.0000118” which translates to the size of the scratch that particle makes on the steel. Most bacteria are measured in the one to ten micron range.) The grain size on honing film is more uniform than it is in most other abrasive applications. 3M claims that 90% of the grit on their honing film is the same size. In the world of abrasives, that’s a very high degree of uniformity. The grit is aluminum oxide, which is much tougher and lasts much longer than the silicon carbide used on the black wet-or-dry sandpaper sheets.
The “film” of honing film is Mylar – tough and waterproof. Though I use the films dry some like to spray a bit of slightly soapy water on the surface to help prevent clogging or glazing of the surface. I buy honing film with the pressure sensitive adhesive (PSA) backing because, while I am a bit lazy, I find the factory applies stickum in a more uniform layer than the one I try to spray on myself (and I do get it on myself sometimes.) The PSA sheets that I’ve used have been reluctant to let go, however, and leave behind a mess of glue when removed from my glass substrate which then needs to be scraped off; making the removed film non-reusable. If someone knows a brand or source for PSA-backed honing film that can be removed and reused, please post a comment for us.
While a honing film setup may have a low entry fee, the sheets do wear out and after umpteen replacements will end up costing more than a set of stones would have if you had started out with them. But for a low-cost sharpening kit, and to find out which grits you prefer to use before investing in stones, honing film is a great way to go. I have two pieces of ¼” glass the size of the honing film sheets: 80µ on one side, 15µ on the other side of one piece of glass, 5µ and 1µ on the other. With this setup, shown above, and the ruler trick, I can prep one of our Krenov-style blades to shaving sharp in less than a minute. Honest.