The triangle-shaped edge is set on a pure copper plate plated with tin, using a metal chisel made of steel called Tagane. Each of those splinters are curved carefully by hand.
The blades (spikes) have slightly different shapes, heights, and arrangements. The difference will affect when you grate a radish. Because the blades are irregular, no matter how many times the radish reciprocates, it does not hit the same surface and can be lowered without having to change the direction of the radish or apply strong force.
As a grater, stainless steel is too hard, and aluminum is too soft and not suitable. Copper has long been used for its hardness and is the perfect material for making a grater. Another advantage of the copper radish grater is that it can be used for a long time by shaving a blade that has become dull and a new blade can be rebuilt.