Final answer:
The hamon on the blade of a Katana sword from the early 17th century is made of steel.
Step-by-step explanation:
The hamon on the blade of a Katana sword from the early 17th century is made of steel. Steel was the main material used in the production of Katana swords, known for its strength and durability. The hamon refers to the temper line on the blade, which is created by differential heat treatment of the steel.