Granite v-block is crisp,so it is afraid of hard
hit.As the result,we should use it carefully.We'd better prevent
some heavy things hitting the v-blocks,lest occuring sags and
crests.
If we don't use it for a long time,we should wipe it
with the special lubricants.If there isn't special lubricants,it
can be replaced by cooking oil.Just dry again with a soft cloth
when we use it next time.