Cover one side of the blade with a very thin coating of clay, I usually water it down a lot. Allow it to dry, then do the other side.
When both sides are dry apply a thicker coat of clay to one side defining the hamon as you go. I put tape on the mune so that it will not be accidentally covered with clay. After about 24 hours turn the blade over and coat the other side.
Heat the blade evenly to critical temperature (Note: This photo shows some cold spots).
Next temper the blade for 1 hour at 200 degrees C.