Lloyd brings out a good point that often gets overlooked when people start talking hardness......The edge may well be harder than the rest of the blade.
Harder edge
1) The thinner section may have better quench results with substandard heating and quenchants. Even when all is good, the thin edge cools far faster than the thick spine. Part of the tang may never get quenched at all.
2) The steel choice may be one that requires longer soaks at higher temps, and the thin edge may get more effects than the thicker spine and tang.
3) The test area is almost always the ricasso or the tang....two places that never cut. Both can be softer than the edge.
4) Testing the actual edge is nearly impossible for the average maker.
Softer edge
1) In other cases, the grinding and inadvertent heating of the edge can make it lower in hardness than the test area.
2) A good reason not to pull the blade from the quenchant too soon is that if it is still hot enough in the thick sections, it can auto-temper the edge and make it loose hardness and edge retention. In worst case scenarios, the edge gets auto-tempered so severely it gets converted back into pearlite. I have seen this happen on edge quenched blades pulled from the quench too soon with a cooled black edge and a still glowing spine. If you edge quench, don't remove the blade from the quenchant until it is all below 200F. Most folks just tip it sideways after the spine looses color, and let it cool in the pan.
