There are several choices, but few as universally relied upon as the low-tech sharpening stone. Diamond stones, which have a very fine grit, are used on knives that only need touched up. For duller blades, approach it much like you’re using sandpaper on a block of wood: coarse-grit stones first (grits of 400 or less); then progressively finer ones (600 and above). For a serrated blade, you’re going to need a cone-shaped taper sharpener which will be made of the same material as a regular stone. For big tools: sharpening pads. Some enthusiasts swear by using oil to sharpen their blades, others go with water, or — in a pinch — saliva.
