I still have an "audiophile" turntable (altho no longer used) fitted with a Keith Monks "fluid damped" arm which instead of the ultra-thin wires from the arm to the base, has three small recesses in the base filled with mercury, in which sit three pins from the arm which lead to the terminals on the cartridge. I used to have a small bottle of mercury which back in the day I had got from a local chemical supply house. It had long disappeared when I moved and lost the mercury in the base. But the owner of a secondhand store said he had some old thermostats which had mercury switches in them, which saved the day.I admit I have not tried it with rust myself. I was told back in the day that it would do the job on rust or anything else likely to be found in a firearms bore, but I have no first hand knowledge of that. I probably should have let that one go rather than passing on maybe bunk info. Since I no longer have any liquid mercury, nor for that matter a rusty barrel on which to try it, I shall pass.