Zaratsu polishing

The name comes from Sallaz, the German maker of the polishing machines Seiko imported in the 1950s. The technique is not a machine process, though: the case is held by hand against the flat face of a spinning tin plate charged with polishing compound, with the angle and pressure controlled by the polisher.

What happens at the lap

The important word is flat. The tool is a rotating disc, called a lap, and the work is pressed against its face rather than its rim. Tin is the traditional material because it is soft enough to hold the abrasive particles in its surface and hard enough not to deform under the work, so the lap keeps its own flatness and passes that flatness to the case. The polisher works through progressively finer compounds, cleaning between stages, because a single coarse particle carried into a fine stage leaves a scratch that has to be taken out from the beginning.

Nothing holds the case except the polisher's hands. There is no jig setting the angle, so the geometry of the finished surface is entirely a function of how steadily the case is held against a moving disc. That is why the training is measured in years and why the operation cannot be undone: every pass removes metal, and a facet polished slightly out of plane can only be corrected by taking more metal off the surfaces around it.

What it achieves

Two things at once, which is the hard part. A mirror surface that is genuinely flat, so a straight line reflected in it stays straight rather than bending, and an edge between two surfaces that stays crisp instead of rounding over. Ordinary buffing on a soft mop does the opposite: it produces a bright surface with a slightly domed profile and softened edges.

The reason is mechanical rather than mystical. A cloth mop is compliant, so it wraps around whatever it touches and cuts hardest at the high points, which are the edges. A rigid lap running true only cuts where the work meets it. The same argument applies inside the watch, where the flat black polish on a steel component is produced the same way, on a flat lap, and for the same reason. Our guide to movement finishing and decoration covers that side of it, along with anglage, the hand-beveled edge that is its closest relative.

Where it came from

The technique arrived with imported equipment, but the reason to use it was a design decision. Grand Seiko dates its case language to 1967 and the 44GS, whose rules, set out by the designer Taro Tanaka and now sold as the Grammar of Design, require flat surfaces and flat mirror finishes, facets meeting at sharp lines, and no visual distortion anywhere on the case. Zaratsu polishing is what those rules demand in the workshop. The history is in our assessment of Grand Seiko.

How to spot it

Hold the case so a hard straight edge, a window frame or a door jamb, reflects in a flat surface. On a well-polished case the reflected line stays straight across the whole surface and breaks sharply at the edge. On an ordinary polish it curves.

Then look at the boundaries. On a Grand Seiko case the mirror flanks meet fine hairline brushed surfaces along a line that should be dead straight and free of any polished halo bleeding into the brushing. A soft or wandering junction line is the tell that the case was finished quickly. The effect is easiest to see on the lugs and the case flanks, and it is the reason the cases look expensive in photographs less often than they do in the hand. The Snowflake is the usual reference point, and it shows the harder version of the problem: its titanium is grayer and gummier to work than steel, so the mirror is less bright and the polishing is more difficult, as our comparison of titanium against steel explains.

Living with a polished case

Flat mirror surfaces show hairline scratches more readily than brushed ones, and on a case whose appeal is its geometry, refinishing is not a routine matter. Every polish removes metal, rounds edges a little and, done badly, replaces a distortion-free surface with a shiny approximation of one. Brand service on a Grand Seiko Spring Drive runs roughly $700 to $1,000 on this site's indicative US figures before sales tax, and case refinishing is normally part of it. You can decline the refinishing, and on a sharp case with light marks that is often the better answer. Our page on service costs sets out the variables.

The common confusion

Zaratsu has become a generic label for any mirror finish, in the way that any bright case gets called polished. It describes a specific method and a specific result, and it is not exclusive to Grand Seiko: Credor and King Seiko cases get the same treatment, and several Swiss and independent houses achieve flat, distortion-free surfaces without a Japanese word for it. What is fair to say is that Grand Seiko applies it at a scale nobody else matches at the price, which is the argument our answer on whether Grand Seiko is worth the money examines. The other confusion is the idea that it is a machine process because a machine spins the lap. The machine turns the disc. The polisher does the polishing.