Questions like that this early in the morning?
Using clay on the spine area to create a hamon is a process created a "few years back" by far eastern sword and military weapons makers to keep the spine area soft and prevent breakage in battle. (If that's not the historical truth, who cares? It sounds cool ) But, that's exactly what it does. It's one of numerous ways to influence distinctive hardening zones in a blade. Depending on the steel type, temperatures and quenchants used, different types of visual signs indicate this differential hardening. The hamon is one of these by-products of selective hardening.
then we get into the difference between hamons, quench lines and hardening lines. (Those last two aren't always the same!)
As a maker, it's can be VERY aggravating to achieve, but one of the most fun things I do.
No two hamons are ever alike.
I'd say I got about 85% martensite conversion on this blade. The hamon is very subtle and unique.
They are what they are.
Hamons can also be achieved with no clay at all depending on time, temp and thickness/geometry of the blade itself.
I hope this helps.
Rather than me type, just check this:
http://en.wikipedia.org/wiki/Bakelite and here's a little info I gave on another site:
"Info is slightly difficult to come by on this. Catalin is ALSO BAKELITE as it was manufactured by the Bakelite Corporation. (Bakelite being the world's first synthetic plastic made from formaldehyde as discovered by Leo Baekland).
Anyway, this is basically the same Bakelite but without the wood fibrous content.
My good acquaintance, Michael Kanter (Adam Michael Knives) pulled a MASSIVE piece of this stuff 1 1/4" thick by about the size of a sheet of plywood off the wall in a basement of a building up in Wisconsin. To it was attached all of the old fuse boxes that were going to get upgraded. I think the building was built in 190? sumpthin'. It was headed for the dumpster!
I traded Micheal for a LOT of it.
That's the story on that."
Hope all that helps!