The Fällkniven DC4 is a compact double-sided sharpening stone. One side is made from ceramics for that fine finish. The other side is a diamond-coated sharpening stone (25 micron) to presharpen your knife. Combined the DC4 is the perfect stone to keep close in your backpack to make sure you never have to use blunt knives. Fällkniven DC4: sharpen even the hardest types of steel on the road. The ceramic stone is made from synthetic sapphire. The advantage of this material is that it, in time, it won't lose its flat surface. This also applies to the diamond-coated side. In addition, with these hard materials you can even sharpen knives made from extremely hard powder types of steel. The stone does not any water or oil during use. You only occasionally need to clean it with warm water and liquid soap. The stone might feel a little rough at first, but will become smoother during use. The leather sheath has a smooth front and a rough back. You can use the back as a strop.