I used to do custom cabinetry and lacquer finishes. We always had to make sure the surface was clean, clean, clean before re-coating, especially with the older refinishing projects. We experimented with everything and came-up with tooth polish as the best for removing ground in soil and petina, specifically found around the handles. I've advised dozens of homeowners of this treatment and it always worked.
The dummy I am, never thought of this once used remedy for my ferrules. Thanks Blud.