Phantom substrate preparation providing distortion-free surfaces.
Sallaz polishing is a processing technique that MINASE excels at. A substrate preparation is applied to cases before finishing, which provides a beautiful, distortion-free surface. The name may sound eccentric, but it derives from Swiss processing equipment in times gone by. In general, watch cases are completed by forging, cutting, and buff polishing. By applying sallaz polishing as substrate preparation before buff polishing, the distortion of polished surfaces is reduced, resulting in a plain, clear, beautiful mirror surface. Sallaz polishing was once also used by Swiss watch manufacturers, but is now rarely used except in high-quality Japanese watches.
One of the reasons is that it mostly depends on the craftsman’s skills. Sallaz polishing enables fine finishing of cases, but it involves the risk that the corners may become rounded unless polished by a skilled craftsman. Cases with rounded corners are not suitable for high-quality watches. However, skilled craftsmen can carry out sallaz polishing without rounding the corners while preparing the case surface. The remaining corners are only 2/100 mm. Even in MINASE, only a handful of craftsmen can adjust the contact between the parts and the polishing disk just by using their sensitive fingertips.
Forging is an indispensable preparatory process for sallaz polishing. Striking a case several times eliminates pores and makes the material denser. By applying sallaz polishing to unforged metal, pinholes rarely appear on the surface, and can be avoided by forging. On the other hand, forged cases need to be annealed in order to eliminate distortion. We still adhere to forging not only because it makes sallaz-polished surfaces more beautiful, but also because we can improve the durability of cases by forging.
MINASE has been studying sallaz polishing for about 30 years. In our newest work, HiZ DIVIDO, sallaz polishing is applied to the dial plate and index in addition to the 14 faces of the case.
This photo shows sallaz polishing of a dial plate of HiZ DIVIDO after cutting. This is called “rough finishing.” The surface to be prepared is gently brought into contact with the rotating disk on which abrasive is spread. According to the polishing craftsmen, it’s like rubbing the part gently with the disk rather than polishing it. Sallaz polishing is normally applied to wide surfaces such as the corners of cases, whereas MINASE applies it also to thin surfaces of just 0.7 mm. The reason why we can perform sallaz polishing of such thin surfaces that other manufacturers never try to emulate is because of our highly skilled craftsmen.
At present, two craftsmen are engaged in sallaz polishing in MINASE, one of whom has no less than 26 years of experience. Nevertheless, even with such experience, he said he was worried about how to apply sallaz polishing to HiZ for a week or so. Sallaz polishing is just substrate preparation before buff polishing, but without appropriate preparation, scratches will remain regardless of how often sallaz polishing is performed. The reason why we can frequently apply sallaz polishing to cases and dial plates is because we are confident that we can properly perform substrate preparation before polishing.
We even apply sallaz polishing to the index of the HiZ Series. Normally, to make an index glossy, its surface is ground using a diamond cutter instead of sallaz polishing. It is also considered to be a high-quality finish, but we are keen to apply sallaz polishing in order to pursue even more beautifully prepared surfaces. It is more difficult to prepare very shallow index surfaces than to prepare cases by sallaz polishing. Nevertheless, we eventually succeeded in providing beautiful surfaces and sharp edges to the index of the HiZ Series.
This is a photo of a partly sallaz-polished case. The cases are repeatedly forged and annealed at 1,120°C, and then a hole is drilled and sandblasting is applied to the entire surface of the case at low pressure. Sallaz polishing is applied only after pressing and cutting traces are eliminated. Sallaz polishing is normally applied only to the surfaces that are to be made glossy, but in the HiZ Series, it is applied as substrate preparation also to the surfaces to be satin-finished. This is because adequate substrate preparation allows more beautiful finishing. We take pride as a watch manufacturer in making utmost efforts even if they are invisible.
This photo shows an almost-finished case and index of HiZ DIVIDO. After the main surfaces are sallaz-polished, glossy and matte surfaces are buff- and satin-finished, respectively. The reason why the glossy part looks black is because of excellent substrate preparation. Careful polishing of hard material makes even white stainless steel shine black. This is called “Black Polish.” There are some high-end watches finished at an equivalent level, but there have been only a few attempts to create both beautifully prepared surfaces and sharp edges like the HiZ Series. After this, surface treatment is applied to complete the case and index.
MINASE has crafted a massive shape having both beautifully prepared surfaces and sharp edges. Generally speaking, the more beautifully the surfaces are finished, the more corners are rounded, and the sharper the corners, the more surfaces are distorted. This is why massive watches are difficult to finish beautifully and beautiful watches tend to be planar. The photo shows indices after being punched out by forging and then sandblasted. After this, sallaz polishing is partly applied to them. It is extremely difficult to apply sallaz polishing to such massive parts.