Shaking
Soot is easiest to remove from leather when it is dry. The more effort you put into the dry cleaning processes, the easier the wet cleaning processes will be. First, shake the leather to remove as much of the soot as possible. Do this outside and don't apply any pressure, as this will only work the soot into the leather.
Sweeping and Vacuuming
Sweeping and vacuuming the leather will remove a lot of the soot from the leather. The hose on your vacuum is the best option as it will suck up the soot without pushing it into the leather. Vacuum the entire piece of leather by holding the nozzle a few inches off the material without touching it. Do this until it is as clean as possible. You may need to go over it several times to get the leather clean. If you don't have a vacuum, sweep the soot off with a brush.
Washing
Washing the leather is the final step to remove the soot entirely. You can easily wash finished leather, but you should get unfinished leather, such as suede, professionally cleaned. Unfinished leather is sensitive to water and dry cleaners have commercial-grade cleaning solutions that will work to remove soot stains. To clean finished leather, soak a clean cloth in water and wring it out as much as possible. Rub the cloth over the leather until it is completely clean. Immediately dry the leather to prevent it from drying out and cracking.
Odor Removal
Leather is a porous textile that will absorb soot smells. Professional dry cleaning will remove these smells, but you can try to remove them yourself first. Fill a spray bottle with one part white vinegar and one part water. Spray the solution over finished leather and immediately wipe it up with a clean cloth. White vinegar is a natural deodorizer. If your leather is unfinished, fill a bowl with white vinegar and place it in the center of a small closet. Hang the leather in the closet and let the white vinegar evaporate into the room to neutralize the soot smells in the unfinished leather.