To sharpen ski edges, you'll need the following:
File in a filing guide
Ski vice (or something to build a platform like a stack of wood or books)
Step 1: Set Up Skis
Before you begin working on your edges, you'll need to get your skis into a workable position. This is where the ski vice comes in handy. If you don't have a ski vice, you can get creative with your platform by using books, wood or anything that will create a stable base. When you feel you have a sturdy base for your skis, move your ski break out of the way. With your skis bases facing up, push your break down so it is out of the way. Secure your break in this position with a thick rubber band.
Step 2: Start Filing
You will need your file in a filing guide to start sharpening your edges. Match the angle of the edge with your sharpening tool, then begin filing. You'll need to work the file in one direction from tip to tail, overlapping strokes as you go. Files usually have arrows on them to indicate which direction you should be working, so be sure that you are following the arrow of the file as you work.
Sharpen your base edges first, and then move on to the side edges of your skis. As you file, use light and even pressure. Focus mainly on the areas that contain burrs (sharp metal bumps on your ski's edges), but be sure to run the file over the entire length of the ski. Take your time as you work, and be sure to keep the file flush with the edge of your skis.
Step 3: Clean Rust Spots
This is where the gummy stone comes in. Use your gummy stone to clean up any remaining rust spots. This handy tool works like an eraser for ski edges. Be sure to check your work as you continue to clean your edges, touching up the base and side edges until you feel your skis are ready to go.
Step 4: Wipe Clean
For the final step, use your towel and rubbing alcohol to wipe your edges clean.
That's it! Now your skis are sharp, clean and ready to hit the slopes. For more skiing maintenance tips, check out this video on how to wax skis. Take a look at the below video for a visual on how to sharpen your edges.