Got some old rusted (partly) iron tools from a friend or your grandparents? These these are usually of higher quality and strength then the basic tools from a local shop. So don't be to quick to put the tools in the trash bin.
Using a steel brush and a file (the workshop tool to treat wood and metal) you can restore the the tools to former glory.
Photo 1: The beginning
Photo 2: The end result
Step 1: Tools and fixation
Find yourself a drill with a high rpm, and don't use a cordless drill since you will be switching batteries every 5 minutes.
Be sure to use a proper clamp to securely fixate the rusted tool! You are using a steel brush at high speed and don't want to shoot into your clothing or other surrounding objects because the rusted tool was not secure enough.
If possible, use a drill with a second handle, this helps positioning and reduces the risk of damaging your own hands.
Step 2: Remove rust
NOTE: Wear eye and ear protection !!!
NOTE 2: There will be very fine dust, so work in a ventilated room or outside.
Use the drill on hign rpm and brush of all the rust. You have to use some force (push the brush hard against the surface) to remove all the rust. Adjust the clamp to be able to reach every part of the crowbar.
The process took about 10-15 minutes for the crowbar in the picture (35 cm long).