... black material: zirconium ceramic Special features of GTT advanced ceramic knife:1. Pantent technology “tape casting to produce zirconia ceramicproducts” ... not get tired after long-time usage.3. Thanks to our patent technology, our knife is flat after firing, no need ... The knife edge and sharpness can last for more than 3 years. Small notch seldom happen. 3",4",5",6",7" high quality zirconia ceramic ...