Very old razor blades that you no longer use, don’t throw them away: used like this they are pure gold.

Throughout the 20th century, razor blades became increasingly sophisticated, with the addition of features such as multiple blades, ergonomic handles and built-in lubrication systems. Today, razor blades come in a variety of options, from disposable to electric, to suit the needs of different people.

Razor blades
To get razor blades to cut again after many uses, there are a few techniques you can use. One is to soak the blades in warm water for a couple of minutes before use. The warm water will help soften the razor hairs and remove any shaving cream or soap residue.
Another technique is to run the blades inside the jeans. The burlap on the jeans helps to remove rust and restore sharpness. However, this technique may not be effective for very dull or rusty blades.

Either way, both soaking in hot water and running inside jeans can help prolong the life of the blades.