Several times I’ve seen the advice to sharpen scissors by cutting tin foil with them. I tried it. What happened was the blades got cleaner. It took off small bits of rust and burrs. They were shiny and maybe felt a little sharper. One site said that if you do that very often you wear away the steel in the wrong places. Sharpening is done at an angle, not straight on as with cutting. Sadly both eHow and www.diylife.com bought into the tin foil sharpening meme. www.diylife.com has space for comments. That’s very helpful so people can contribute counterpoint to the articles.
I looked into the angles for sharpening. The angle ranges from 12 degrees to 35 degrees. The larger the blade the larger the angle should be. A machete gets 30 degrees, and an Xacto knife gets 12 degrees. It’s best to use the angle the manufacturer originally put on the blade. Most sharpening is done with a sharpening stone. Details on how to do this can be found at www.wikihow.com/Sharpen-a-Knife. It’s possible that your local butcher might sharpen a knife for you at little or no charge.