How do you keep a hand forged blade from rusting if you actually use it?

Those dark spots are patina starting, and honestly that's a good sign for a working blade. High carbon steel like railroad spikes (the HC ones anyway) will darken with use, expecially cutting green grass and brush. The juices and acids in the plant material react with the steel and give you that mottled grey-brown look. Rust is different: it's orange, rough, it'll flake and it'll rub off on your fingers. Patina is smooth, dark, and actually protects the steel underneath a bit. That said, patina can turn to rust if you baby it wrong. Wipe the blade down when you're done for the day, don't leave it wet overnight, and hit it with a light coat of oil. I use camellia oil but any light mineral oil works, even the food-safe stuff from the kitchen aisle. On the hammered spine you'll want a bit more oil and maybe work it in with a rag because the texture does hold moisture in the dips. A smooth polished edge just needs a quick wipe and it's done. As for using it, use it. A sickle made to cut grass should cut grass. The maker forged it with a twisted handle and a hammer finish for looks, sure, but the edge is polished and sharp for a reason. And here's the thing about patina: it only looks good once it's earned. A blade that's darkened from actual work looks way better than one that darkened sitting in a drawer. I've got a few spike knives I made years back that I use around the yard and the ones that got used look the best now.

If you're worried about wrecking it, just don't go hacking into dirt or rocks. Grass and light brush is exactly what it's for. Keep the edge touched up with a strop or a fine stone and it'll last generations. Your grandkid will be out there cutting the same weeds with it someday.

Agreed on the use it part. I've got a spike hatchet I hung on the wall for two years because I liked the look of it, and when I finally just started using it the finish settled into this even grey that looks better than the day I got it. Now I keep an old cut up t-shirt and a squirt of 3-in-1 hanging on a nail by the shed door, wipe everthing down before it goes back on the rack. Takes ten seconds and I've never had a problem since.

Still finding my feet here so sorry if this is a dumb one, but I've got an old machete my dad left me that went through the same thing. What nobody warned me about was the sheath. I kept it in leather for months and it came out with weird black spotting that took forever to clean off. Turns out the leather holds moisture against the steel. Now it lives on a hook, naked, and only goes in the sheath for carrying. Is that an issue with the twisted handle too, or is the texture open enough to breathe? It seems like the twists would trap gunk from the grass as well.

The twisted handle's the sneaky part nobody thinks about. Mine collects grass sap and dirt down in the twist and if I ignore it, it gets grimy fast. I run an old toothbrush with a drop of dish soap over it now and then, dries quick on a hook. Curved edge is a bit fiddly to sharpen too, I just drag the corner of a fine stone along the inside following the curve, works fine for grass. And yeah, use it. Mine's got two seasons on it and the darkening on the spine actually shows off the hammer marks better than when it was new.

Update: took it out for another afternoon and just let the dark spots happen, the t-shirt and a wipe of oil afterward like the hatchet guy said. Evening grey is starting to look even, which is weirdly satisfying. Also tried the toothbrush trick on the twist - yeah, there was more gunk in there than I want to admit. One thing though, mine came with a stitched rawhide sheath, is that same leather spotting risk a rawhide thing too or only tanned leather?