I keep a covered bucket of this stuff in the shop, adding water or other elements as needed for proper consistancy.
4 parts "yellow" Iowa Bank clay or any kind of clean clay that you can find.
2 parts sifted clean wood ash
1 part powdered charcoal ( crush with Mortar & pestle )
1 part powdered soft firebrick ( crush with Mortar & pestle )
Add water to and let slake ( soak ) for at least 1 hour then remix and adjust water as necessacary to get a consistancy like a thick milk shake.
To apply: Take a small amount of clay slurry in a mixing cup add a splash of water to thin it out and mix using a brush. Clean the freshly sanded /ground blade with acetone or spray brake cleaner (to de-grease). Apply a very thin coating of the clay slip to the entire blade, allow to dry, I set it in the sun, or if its cold out I'll put it in the shop toaster oven, yes! a Toaster Oven every shop needs one. I paid $3.00 for mine at a 2nd hand store.
Once the first coat is dry, with a fine tiped artist's paint brush lay a series of thin 1/8 - 3/16" lines of clay running from spine to edge spaced between 0.5-1.5 inches depending on the size of the blade and the asthetic desired. (thicker clay for thicker blades ) make sure each side roughly matches the other to reduce the chance of warping. Allow to dry again, when dry use a bigger brush/spatula/popsicle stick ....to apply 1/8" to 1/4 " of clay
(depending on size and thickness of the blade ) to the the sides of the blade in a pattern that is pleasing to your eye, once again keeping things even from one side to the next. As a general rule of thumb the coating should be on about 1/3 to as much as 2/3 of the blade depending on the width, but remember you DON'T want the temperline too close to the edge or tip. Also to reduce the sabering ( curving ) effect of differential quenching make sure to clean the clay from the blade's spine. Allow to dry a final time and "Fire" in the Toaster oven at 400-500 degrees for 30 min or so to drive out any remaing moisture.
Heat, quench & temper according to the steel specs, I find that 1084 & 1095 produce the most predictible temper line results for me. Polish with waterstones and or or wet sandpaper. Lightly etch with warmed vinegar to darken the temper line.
WOW ! I actualy managed to get that down with out using any samuri sword slang
Remember to keep and share notes folks.
Jens Butler
Oakwood Forge