Re: "blocking" with japanese sword
If you are absorbing the totality of an enemy's blow with the side of a blade, the blade will bend and the edge will crack (because the blade is more thin side to side than front to back). To absorb a full blow you should most certainly use the back of the blade. I personally have never seen a shinken technique which involves taking a full blow, however. If such blocks are taught to you, it is likely kihon waza and is meant to address underlying principles rather than teach field technique. I believe that redirection, "slapping" blocks, and sliding displacements are generally more reasonable. In addition, if you enter conflict worrying about your weapon taking damage, the day is surely lost. A sword's value is the life of the human that wields it, not how purdy it is.