Most production knife manufacturers produce what are called 'all-hard' blades. That means the blade is the same hardness throughout. This is a much easier way to make a knife blade. Almost all stainless steel blades are heat-treated in this manner. Carbon steel blades are more frequently made with differential heat-treatment by some smiths.
The American Bladesmith Society requires candidate members (journeyman and mastersmith levels) to test knives in such a way (slicing, chopping, and finally bending) that differential heat treatments are required to pass the test. This is the proper term for a blade which has a hard edge and a soft spine. Often blades that have been heat-treated in such a manner are etched lightly to show the temper line, or the line which distinguishes the hard part of the blade from the softer. There are different ways of creating and showing this demarcation. In a older Japanese sword, this line is called the hamon, and it character is very important to the overall aesthetic properties of the blade.
Differential heat-treatment is more time consuming that making an 'all-hard' blade. It's benefits in the real world of knives are debatable. Many ABS Mastersmiths make their damascus blades all-hard (a single hardness) because doing a differential treatment will not add functionality to the blade (particularly in the sub five inch range), the temper line can not be displayed in a pattern-welded blade without distoring the pattern, and it will cause unnecessary time and expense.
None of the manufacturers your friend names are making differentially heat-treated blades. If you want to know more about heat-treatment, look at this thread:
Heat-treatment, what is it?, and look at the web sites of ABS masters like
Ed Caffrey and
Don Fogg. The testing criteria for the American Bladesmith Society can be found here:
ABS site
Hope that helps!
Paracelsus
[This message has been edited by Paracelsus (edited 04-14-2001).]
