From my personal experience, I took the laser-cut pieces of my drop spindle whorls and soaked them in water before coloring or stitching. I found a lot of the laser soot was removed, and I could just wipe off any residue. It didn’t smear into the leather surface or engraved area; much cleaner than trying to wipe off with 91% iso alcohol.
Edit: my leather was a garage sale find; I think it was at least a few years old. After the laser operation, I soaked it since it felt stiff and dry. Once dripped out and press-dried with a towel (force, no heat), it responded to paint and modest tooling nicely.