As the stones and woods grow, they will have straight and cross grains. Diamonds also have that. When we try to cut with a straight grain, there is no stress and can be cut easily. On the other hand, when it comes to a cross grain, it is like a one way road, and cannot be cut in anyways. The diamonds are one of the hardest materials to start with, so it is not like cutting a paper with scissors. When we put a grinding machine against the cross grain, it just makes metallic clank, and never cuts.
I always wanted to see when the diamond catches a fire, so I once tried.
I put a diamond on a grinding machine against to a cross grain. The diamond was heated little by little, and suddenly it turned into a red color. When I continued grinding, the color becomes more transparent, and became a beautiful red. I was watching it with half fear and half excited expecting it might catch a fire. However, it didn’t, and outdone in patience.
Thinking that the rough diamonds came out to the surface of the earth from the deep under the ground with blazing heat, it would not be burn. So human’s common sense doesn’t work so practical.
