These are the sheets that after cut out knives. These knives are put into the heat treating oven. By heating knife steel in the high temperature(1100℃/2012℉)heat treating oven then quickly cooling it, the knife steel will become much harder, also more brittle. Of course they recycle those sheets for "GREEN".
Is the whetstone only way to sharpen knives?
This is the "wooden sharpening tool" for professional use. Some professional use wooden sharpening tools, like a wooden block, for finishing. Sharpening a knife on the whetstone leaves fine hair line on the surface. To remove this hair line and polish the knife the wooden sharpening tools work excellent!