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.