Bench jewelers hate to throw out used tools. By training and by nature we try to conserve the materials we use. An unfortunate side effect is that old burs and dull files tend to collect on our benches.
All is not lost, however. There is life in those tools yet. A "Sneaky Goldsmith Trick" with chemicals in your workshop can get them sharp and useful again.
Warning: Only bench jewelers who are familiar with the safe use of chemicals should try this trick. Acid can cause serious injury if they are not used properly.
First, prepare a very strong pickle solution (an acid solution used to clean oxides and fluxes off precious metals) about twice as concentrated as usual and as warm as normal. Thoroughly clean your dull files and burs while the solution is warming. Start with an ultrasonic cleaner followed by a blast from the steamer. Continue cleaning until all traces of stuck metal are removed, then degrease using alcohol or another grease-cutting cleaner.
Once clean, completely submerge the tool in the pickle solution. It should be placed on edge on the bottom of the container or suspended in the solution. Burs should be suspended so only the cutting portions of the tool are submerged in the acid.
You will soon notice small bubbles beginning to rise from the surface of the tool. This is gas being released as the solution begins to dissolve the steel surfaces. Let the acid work for a few minutes, then remove the tool from the solution and rinse in baking soda and water to neutralize the acid. Dry it immediately to prevent rust.
You'll have to experiment with the exact amount of time you need to sharpen your tools this way. You should only leave them in the acid long enough to etch the cutting edges to restore sharpness; any longer and they will dissolve too much.
This method can be used once or twice on a tool. After that the cutting edges become too degraded for further sharpening, but don't toss them out yet. There are other "Sneaky Goldsmith Tricks" they can be used for…but that's another story
The pickle solution to dissolve steel also becomes useful with the dreaded broken drill problem. It's not uncommon for the tiny drill bits to break off and leave part of the drill wedged into a blind hole of the piece you are working on. These pieces are virtually impossible to extract by mechanical methods without doing grievous harm to finely polished surfaces on the surrounding metal.
Mix up a fresh acid solution as described above. (Don't use old solution that may contain dissolved copper, which will plate out on the jewelry, leaving a pink coating on the surface that can be very difficult to remove.) Leave the item in the acid until the gas bubbles stop forming and the steel is entirely dissolved.