Regarding gripping a katana and "shibori".

"shibori" originated as a term describing how weavers in Japan would wring the dye out of silk cloth as it was being made. Unfortunately, while the term directly translates to "wringing" there is a major difference between "wringing" in Japan and "wringing" in America.

Americans wring cloth by twisting it up in a spiral (and the act of twisting into a spiral is called "wringing"). In Japan, the cloth is twisted first, and then once it is tight wringing begins by squeezing the cloth along it's length. So, "shibori" only begins once the cloth is twisted as tight as it can move. Another translation for "shibori" is "contraction; squeezing; choke" and that is more of what we are referring to. I prefer the term "te no assai"; "crushing hand".

Properly done, shibori is a crushing or squeezing of the hands, a tensing of both arms and with a very slight inward pressure of the wrists; all done at the same time. WHEN you do this will depend upon your particular school and possibly your level of training.