Early on rods were dipped in what was called a lime slurry or used bare the loose flux came about early in the 20s I think but they can indeed be used bare. No way would it be an acceptable way to weld today, nor is there any need to, but it actually was done quite a bit. That old Page dragline I mentioned was welded using bare rod for most of the house structure while most of the supporting structure was riveted, not sure what was used on the boom but from the looks of it a fluxed rod of some type was used. Bare wire can be very difficult to use but once the arc is established the weld is not nearly as bad as one might think, it actually looks almost like a 6010 weld. When I first heard of doing this I was sure the weld would be full of holes and generally just a mess that however was not the case at all. The only times I have done this was just out of curiosity and a couple of times to show someone how it was done way back then.
The first I ever heard of using bare rod was reading an old General Electric welding manual from sometime in the late teens or early twenties, actually a reprint of an old book. This was more for welding equipment than the actual welding process but they had that chapter on how to weld and a chapter on job safety, that chapter was absolutely hilarious! The safety suggestions and rules had to be seen to be believed and that section was why we had the book in the first place, one of the mines bought them to use at their annual re-training classes to show just how much things have changed. It had things like choosing safety gear, like this little gem "some welders choose to wear gloves on their hands but most prefer the dexterity of the bare hand" and this one "the face and neck should be covered to prevent exposure because they are not as resistant as the hands and will suffer scalding"
They even had a brief description of "darkening welding glass with soot" but did go on to say that "sufficiently dark glass is now obtainable to make this unnecessary", OSHA and MSHA would have loved those guys!