A katana is not machined. It is built up, hammer blow by hammer blow, from a block of raw steel into a curved blade that can hold an edge without shattering. The process has barely changed in six hundred years, and understanding it explains almost everything about why one katana costs $150 and another costs $1,500.
1. The steel
Everything starts with the carbon content of the steel. Too little carbon and the blade is soft and will not hold an edge. Too much and it becomes glass: sharp, but brittle enough to snap on a bad cut.
Traditional Japanese smelting produced tamahagane in a clay furnace called a tatara, burning iron sand and charcoal for three days. Modern forges, ours included, work with standardised high-carbon steels — 1045, 1060, 1095, T10 tool steel, or folded Damascus — because the carbon content is consistent from bar to bar. We cover the differences in our guide to katana steel types.
2. Folding and forge welding
The steel is heated to around 1,000 °C, hammered flat, folded back on itself, and welded shut under the hammer. Repeat that ten to sixteen times and you get thousands of microscopic layers.
The romantic story says folding makes the blade stronger. The truth is more interesting: folding homogenises the steel. It burns off impurities and evens out carbon that was unevenly distributed in the original bloom. With modern steel, which is already uniform, folding is mostly an aesthetic choice — it produces the rippling grain pattern collectors look for on a folded blade.
3. Shaping the blade
The billet is drawn out into a long bar, then the smith establishes the geometry that defines the sword:
- the shinogi, the ridge line running the length of the blade
- the kissaki, the tip section, universally considered the hardest part of the blade to forge and polish correctly
- the nakago, the unsharpened tang that disappears inside the handle
At this stage the blade is still straight. The curve has not happened yet.
4. Clay tempering — where the curve comes from
This is the step that makes a Japanese sword a Japanese sword. The smith paints a slurry of clay, charcoal and stone powder along the blade: a thin layer over the cutting edge, a thick layer over the spine.
The blade goes back into the fire, then into water. The thinly coated edge cools almost instantly and transforms into martensite, extremely hard. The thickly coated spine cools slowly and stays pearlite, softer and springy.
Martensite occupies more volume than the steel it came from. As the edge expands and the spine does not, the blade bends away from the edge on its own. The famous curve of the katana is not hammered in. It appears in the quench, in about two seconds.
The visible wavy line left at the boundary between the two zones is the hamon. A real hamon is a structural feature of the steel, visible in the crystal itself. An etched or acid-printed hamon is surface decoration — one of the quickest ways to tell a genuinely clay-tempered blade from a decorative one.
5. Polishing
A polisher will spend longer on a blade than the smith did. The work runs through a ladder of water stones from coarse to impossibly fine, each one removing the scratches of the last. The final stages use stone fragments barely thicker than paper, held against the steel with a fingertip.
Polishing does not just make the blade shiny. It sets the final geometry of the edge and brings out the hamon and the grain. A badly polished blade with good steel will look worse than a well polished blade with average steel.
6. The fittings
The bare blade is then dressed. Each part has a job:
- Habaki — the collar that wedges the blade tight in the scabbard so it does not rattle or fall out
- Tsuba — the guard, and the one component collectors treat as an art object in its own right
- Tsuka — the handle: a wooden core, wrapped in rayskin (same), then bound in silk or cotton cord over the top
- Menuki — small ornaments set under the wrap, positioned where the palm grips
- Mekugi — a bamboo peg, and nothing more, holding the whole sword together through the tang
- Saya — the lacquered wooden scabbard
That bamboo peg surprises people. Bamboo is used deliberately: it flexes under shock instead of shearing, and if it ever does fail it fails visibly rather than silently.
How long does it take?
A production blade moves through a workshop in days. A high-end clay-tempered piece takes weeks, most of it in polishing and fitting. A traditionally smelted tamahagane sword made by a licensed Japanese smith takes months, and Japanese law limits how many each smith may produce per month.
What this means when you buy
Price in this category tracks labour almost perfectly. Steel grade, whether the hamon is real or etched, whether the fittings are cast alloy or hand-finished, and how many hours went into the polish — those four things account for nearly the whole spread between an entry-level blade and a collector's piece.
Browse our traditional Japanese katanas, or see what our customers buy most in best sellers.