Black Surgical Arkansas (Ultra Fine): This is the hardest of the Arkansas stones and was traditionally used to sharpen dental tools and scalpels, hence the name Surgical. The Black Arkansas will hone a polished, very sharp razor sharp edge on knives and tools. Black Arkansas stones are used by the most discerning chefs, sportsman and woodworkers. Color can vary from dark grey, to blue/black to black. Genuine Arkansas stones are 100% quarried in the Ouachita Mountains of central Arkansas. They are highly sought after worldwide for their superior ability to sharpen knives and woodworking tools, as well as to put surgical quality edges on a wide variety of instruments Arkansas stones produce these fine edges s with less wear that man-made stones. Arkansas stones are classified as Novaculite, which is extremely hard and fine grained rock containing almost pure silica. These stones are classified in 4 grades and progress from Soft to Hard to Translucent and finally to Black. Each grade is based on the specify gravity or density of the mineral and not the grit or particle size. The grades with more dense or tightly packed particles will produce a finer or sharper edge. In addition, stone grades are not determined by color, as color alone will not differentiate the hardness of different stone grades. Each grade may contain any of the following colors: black, blue- black, charcoal, grey, white, multi-color, brown, pink or red, or a combination of these colors in a single stone. These stones come in a leather pouch to protect them when not in use. All Arkansas stones work best with light mineral honing oil to suspend the metal particles produced by the sharpening process which prevents clogging of the pores of the stone.