*These are the most simplified process.
Hagane (Hard Steel, around 1% carbon)
High-carbon steel that forms the edge of the blade which contains around 1% carbon (depending on the type of steel such as White #1 and White #2).
The steel used here is Yasukihagane Aogami #2 which is also called Blue #2 Steel in common.
Step 1. Hagane Kiri (Cutting the hagane)
The reverse side is sharpened to give it a wave—like pattern. This pattern is only for Blue Steels on the other hand White Steel does not have wave pattern and it is
straight. And this pattern is called "Montan".
Step 2. Jigane (Soft Iron)
The flexible ore becomes the base (less than 0.03% carbon).
Step 3. Temporary Welding
A mixture of boric acid, borax and iron oxide are used in between the hagane and jigane to assist in the forge welding, and it is hammered together at approximately 1,000℃ (1,832℉).
Step 4. Proper Welding to Half Shaping
The metal is formed into roughly the shape of a knife.
Step 5. Shaping Handle Core
The part that will enter the handle is hammered out.
Step 6. Hammering Out
The biade is hammered out to the desired size and thickness. It is then cooled down slowly from 750℃ (1,382℉).
Step 7. Hammering Off
By hanmmering oxidized iron is taken off from the side of the knife.
The knife is roughly pounded by using a belt hammer.
Step 8. Brushing
Using a grinder and a buffer, the hagane on the reverse side is smoothed down.
Step 9. Leveling and Cutting
The blade is smoothed out even further using a belt hammer. A line is drawn showing the prescribed size, and excess parts are cut off.
Step 10. Grinding
Shape is given using a grinder and belt sander etc.
Step 11. Mud Coating and Tempering
A thin clay/mud is spread on the blade, and once it is dried it is heated to 780℃ (1,436℉) then rapidly cooled in water (this is the hot process).