George, The instruments used in the video are sickles, which are different from scythes. I own both scythes and sickles. To give a little explanation regarding scythes, there are two main types of scythes: the American Scythe, which has a heavy hardened blade and a bent handle(snath); and the Austrian/European Scythe, which has a light, less hardened, blade, and a straight or slightly bent(just at the tip) snath. The American scythe is sharpened with either a file or a coarse whetstone(cigar stone) as its primary sharpening instrument while the Austrian scythe is peened in order to establish the primary bevel. Both scythes are finished off with a medium to fine grit whetstone(canoe stone) to give them their final edge. The spine for the American Scythe blade has a ridge established on the outside edge of the blade, kind of like an upside down V. This performs two functions, to provide an angle guide for the canoe stone to give the right sharpening angle for the blade, as well as a mild reinforcement of the blade. The Austrian scythe has an L shaped vertical cross-section. The ridge(rib) at the outer edge of the blade provides the main rigidity and reinforcement for the softer metal.
Sickles are one-handed tools, while a scythe is a two-handed tool. Attached are pictures of my Austrian scythes, my American scythe, and some of the sickles I have bought. I want to make my own, very large, sickle, like the ones the ladies are using in the video. Based on what I can observe, it appears they are made of hardened steel and have a fuller in the middle of the blade.