I sometimes nip over to a place that sells secondhand tools from house clearances and so on, I have likely rehomed quite a few dead mans tools.
Anyway, quite a few have a good bit of rust on them and in order to see the details of the stamps on them I usually give em a rub over with Garryflex blocks (not with old handsaws as they have been etched and it removes too much for that) and by and large that does the job nicely.
Garryflex blocks are basically like a jumbo industrial version of pen erasers. Rubber block, impregnated with an abrasive.
As they're rubber they have a bit of give and get into nooks a bit better than most abrasives.
They come in several grades and for the rough work of just getting the stamps visible I start off with a fairly coarse (red) one.
Years ago I used to work as a welder and weld inspector and when I did my Lloyds tests the welds were bent 180 degrees round a radius, cut across, then acid etched to show the various runs that made up a multipass weld and expose greater detail in general.
Given the choice, I'm not right keen on messing about with stuff like phosphoric acid anymore than I absolutely have to.
Make what you want from all that and it might not work for you but even if it doesnt, those blocks are great for cleaning other tools up.
