Instead of big thick globs of clay, try an even thinner layer. ( look at Charles' photo)
I recommend the following procedure:
Coat the entire blade with a thin wash of satanite. About as thick as runny pancake batter is good. Let dry overnight.
Make the pattern on one side of the blade with satanite about as thick as sour cream. Put it on about 1/16 of an inch thick. In no case should it be more than 1/8". Let dry several hours.
Turn blade over and repeat the pattern on the other side. Try to match the height and shape evenly on both sides. Let dry overnight.
Do the quench as usually, assuring a full soak and even heating. A HT oven is great for this.
TIPS:
A hair dryer is great for speeding the drying up after the wash and between sides.
If concerned with unwanted sori, or fear edge cracks, scrape the clay off the spine as you apply it.
The clay pattern is not necessarily the exact place the hamon will be. In most cases it is a bit more toward the edge ... but that can't be counted on. A test quench on a beveled piece of the same metal will give you an idea where to place the clay. If in doubt, make it higher than you want. A high hamon is still OK, if it dips to the edge .... you have to do it over again.
Use a popsicle stick to apply, shape, and smooth the clay. Popsicle sticks ( AKA craft sticks) are also great for mixing and applying epoxy, shimming hidden tang handles and tsuka, and lots of other shop tasks. Get a box on ebay - 100 for $5 or 500 for $10.
Comment:
Many people don't quite understand the reason for the clay in attaining a hamon. Some think it is to insulate the upper part from the heat in austenitization. That is wrong. For an active hamon to form, the steel under the clay needs to be the same temperature as the edge. What the clay does is delay the cooling of the upper part during the quench. This allows the edge to harden into martensite while the upper part drops into pearlite. The boundary between the two is the hamon. Additionally, the two structures polish and etch differently, thus giving the classic hamon look.
If the clay is too thick, it delays the cooling, but also retains too much heat. This excess heat bleeds down back into the edge and in-hardens it. Having just enough clay to retard the quench about 1 second on the upper bevel is all you want.
The reason you need a shallow hardening steel (one that requires a very fast quench) to attain the different structures. Steels with little alloying and low manganese are what you want. 1075, 1095, W2/W1, Hitachi white #1, etc.
1084 varies in manganese content and alloying, but will usually make a fair hamon. Steels like O-1, 5160, and 52100 have too much alloying to harden fast enough. Air hardening steels, like A2 and stainless steel take far too long to harden, and will not produce a dual structure hamon.
