Here's another experiment I just tried: making abrasive paste from vaseline & powdered baking cocoa. I got the inspiration from a survival article about how to start a fire w/a can of soda & a chocolate bar (use the chocolate as a polishing rouge to turn the bottom of the can into a parabolic mirror). Feedback from people who have tried this says that the cocoa is much less abrasive than polishing compound so it's a lot more work.
After my own experimentation, it's hard to say whether the cocoa paste is finer than the auto compound. It certainly smells better :-) The razor was of course sharper after polishing w/the cocoa paste (sharp enough to accidentally nick my belt strop), but I can't tell if it's because the cocoa is a finer abrasive, or simply because of the additional polishing. I suspect the size of the ground cocoa particles is not as tightly controlled as the grit in the auto compound & wouldn't be surprised if there's a big variance from can to can.
Anyway, these primitive methods seem to do the job, & may not be any more primitive than the methods that were in use 100 years ago (how tightly was the oxide abrasive controlled back then? Could they even measure a micron in 1905?). At the moment I can't say how well these methods compare to modern methods like waterstones, but it's food for thought, & a viable alternative for the chronically short of cash.