some people rub it down with leather and get it hot, but that's a bad idea - no matter how many times they say it. when you rub a string down with leather and get it hot it doesn't spread the wax through the string. the wax heats up and actually leaves the center of the string and heads for the outside. its the last step in string making to get the wax out of the middle so the fibers lay correctly and you get a correct length.
Gibblet,
I'm not following you. It seems like you're saying that you shouldn't use leather to get the wax warm, but then you say the last step in making a good string, is to get the wax out of the middle so the fiber lay correctly. This seems contradictory. Are you trying to say that the fibers will lay correctly only when the wax is in the middle?
String material is pre-waxed and the string making process doesn't heat it up. Maybe you trying to say that you need to get this existing wax out of the middle of the string?