Zaratsu Polishing, Explained: Japan’s Distortion-Free Mirror Finish

If you have heard the word zaratsu, it is almost certainly because of Grand Seiko, whose blade-like cases turned a workshop term into a collector’s password. But zaratsu is simply the Japanese pronunciation of Sallaz — the Swiss-built polishing machines the technique is practiced on. MINASE, the small manufacture we represent in New York, still uses the original spelling.

By MINASE’s own account the discipline originated in Switzerland and largely faded there with time; it survives because Japanese casemakers adopted it and never stopped.

The difference is mechanical. Ordinary polishing happens on a soft buffing wheel that conforms to the part: metal gets shiny, but every edge rounds over and the surface goes microscopically wavy. Sallaz polishing happens against the hard, dead-flat face of the rotating plate, so the surface stays a true plane. The payoff is not extra shine — it is geometry: reflections stay straight, and where two polished planes meet, the edge stays sharp enough to catch light in a single clean line.

The machine only spins. Everything else is human. The polisher holds the case against the plate and reads the contact through their fingertips — angle, pressure, heat, time — correcting continuously by feel. MINASE quotes the working margin at roughly two hundredths of a millimeter — hold the part a breath too long, or a degree off-axis, and a crisp corner rounds over, with no undo.

At MINASE the discipline is applied with almost unreasonable totality. Not just the visible flanks: structural components, the dial’s applied indexes and every bracelet link cross the plates before assembly. A single part can absorb up to 90 minutes; the brand reports one FIVE WINDOWS case involves some 45 polishing operations across 14 faces, and an experienced polisher finishes six to eight cases in a day. It is why MINASE builds a reported five hundred or so watches a year, each essentially made to order.

Here is the entire subject in one image. Both surfaces below are “mirror polished.” The difference is flatness: a buffed surface undulates, and its reflections wobble like the back of a spoon. A Sallaz-polished plane returns the world exactly as it is — straight lines stay straight. Drag the divider and watch the window frame’s reflection.

The technique survives in three very different houses, and the contrast is the story.

Grand Seiko is the reason the world knows the word: distortion-free polishing at genuine industrial scale, by trained specialists. It is the reference point, and it deserves to be.

MINASE is the opposite pole. Its parent, Kyowa Co., began in 1963 as a precision toolmaker — its step drills machined the crown holes in other companies’ watch cases — became a case manufacturer for the industry in 1973, and only launched its own brand in 2005, in the Akita village of Minase that names it. Where most brands polish the surfaces you see, MINASE runs the entire exterior across the Sallaz plates, then builds the watch so it can be fully disassembled and re-polished decades later — its patented MORE construction. Mirror polishing as a philosophy of ownership.

G-SHOCK MR-G is the school nobody expects. Casio’s flagship line, born 1996, is assembled at Yamagata Casio’s Premium Production Line, one technician per watch, and its own account of the line’s finishing invokes Sallaz polishing by name. On the MRG-B5000, the bezel is built from separately polished components, each worked individually before the case comes together. It is the technique’s stress test: mirror facets on a 200-meter solar titanium instrument designed to be dropped.

No spec sheet will tell you a case is well polished — finishing is the one dimension of watchmaking that has never been reduced to a number. But your eye can be trained in about a minute. Four checks, in order of reliability:

Here is the observation we keep returning to at the showroom. The watch industry has spent a decade in a specification arms race — alloys, hairsprings, power reserves — because specifications are easy to sell at a distance. Hand finishing stayed out of the race because it cannot be printed on a spec sheet — and so it has become the last place where a small Japanese manufacture can quietly out-deliver houses charging multiples of its price.

Run the arithmetic on what you have just read. If a single part can absorb up to 90 minutes at the plate, the polishing hours in one MINASE — case, indexes, every bracelet link — rival the total build time of many far more expensive Swiss watches, and that hand-time is bought for four to seven thousand dollars. The logic holds at Casio too: nowhere else does a solar tool watch carry individually mirror-polished bezel components. In both cases you are buying labor the spec sheet cannot see.

Photography is part of the problem: a flat mirror proves itself only in motion — the most convincing thing a watch does in the hand, and the least convincing on a screen. Some things have to be seen.