Forging Tamahagane steel, the traditional steel used for Japanese swords, is a complex process that involves several stages. Here is a general overview of how Tamahagane steel is forged:

1. Material Preparation: Iron sand (satetsu) and charcoal are the primary raw materials used in the smelting process. The iron sand is carefully selected for its quality and purity. It is mixed with charcoal, which acts as a reducing agent.
2. Smelting in the Tatara: The iron sand and charcoal mixture is placed in a clay furnace called a tatara. The tatara is heated and maintained at high temperatures for several days. The heat generated by burning the charcoal causes the iron ore in the sand to reduce and fuse together, forming a spongy mass called a "bloom."
3. Consolidation and Shingling: The bloom is removed from the furnace and broken into smaller pieces. These pieces are stacked, reheated, and hammered to consolidate and remove impurities. This process, known as shingling, involves repeatedly folding and hammering the bloom to eliminate slag, impurities, and carbonize the iron.
4. Refining and Folding: The consolidated bloom is further refined through a process of repeated folding and hammering. The swordsmith folds and welds the steel, layering it to achieve a desired carbon content and uniformity. This folding process helps distribute carbon evenly throughout the steel, creating a blade with desirable qualities.
5. Heat Treatment: After the desired shape and thickness are achieved through further forging, the blade is heat-treated. The blade is heated to a critical temperature and then quenched in water or oil to harden it. This rapid cooling creates a hard, brittle structure.
6. Tempering: The hardened blade is then tempered to reduce its brittleness and improve its toughness. The swordsmith carefully reheats the blade and allows it to cool slowly, which helps relieve internal stresses and achieve the desired balance of hardness and flexibility.
7. Finishing: Once the blade is forged and heat-treated, it undergoes extensive polishing. Skilled artisans use various abrasive materials and polishing techniques to remove any surface imperfections and reveal the steel's true beauty. This polishing process brings out the unique grain pattern of Tamahagane steel.

The forging of Tamahagane steel requires not only technical expertise but also a deep understanding of the metallurgical properties of the material. It is a time-consuming and meticulous process that involves multiple stages of shaping, folding, and heat treatment to achieve the desired qualities of a high-quality steel for Japanese swords.