3. Using acetylsalicylic acid found in aspirin drug:
 Put the wire (end) on top of the aspirin tablet.
 Now using hot soldering iron, press against the wire (and tablet).
 Hold for 2-3 sec, then check for removal of coating.
 Repeat the process if necessary.
 Clean the wire.
This can be combined with usage of smooth sandpaper (see 2).