Sallaz polishing for Minase watches

For its cases, Minase uses the Sallaz polishing technique. You’ve probably heard us talking about it many times, but do you know what is it ? Also known as black polishing, the Sallaz polishing technique is employed to finish steel parts of a watch to create a mirror-like surface. True sallaz polishing is done by hand and only found in high-end timepieces.

What is Sallaz (sarazu) polish ?

Sallaz polishing (most commonly known as black polishing), is also called mirror or block polishing. This technique of finishing is used to give steel parts a surface so perfectly smooth that it seems to be black from certain angle. The technique is time consuming and needs great skills, this is why it is only found in true haute horlogerie watches like Grand Seiko, Glashütte, and of course Minase.

Even at Minase, only a handful of craftsmen can adjust the contact between the watch parts and the polishing disk just by using their sensitive fingertips. The remaining corners are only 2/100 mm, so, the risk that the corners become rounded is high. Kyowa, Minase’s mother company, has been studying sallaz polishing for about 30 years. On the Divido, Minase does not just polish the 14 faces of the case, but also the dial plate and index.

Sallaz (sarazu) polishing at Minase

Minase cases are first polished in a machine that blows air with tiny particles of glass. The craftsmen must wear gloves to prevent getting cuts. After this first raw polishing step, the cases are further polished with the Sallaz technique. First, the craftsmen use a tin plate coated with a very fine layer of diamond dust. The tin plate is rotateing in a circular motion and the craftsmen polish Minase’s cases by hand. This requires an impressive level of skill and dexterity. Each time a surface of the case is polished it goes into a bath to be cleaned before undergoing a second round of Sallaz polish on a smaller plate, and then another bath. This process is repeated for each side of the case. It takes 45 operations to finish the polishing of a single Minase 5 Windows case. A skilled, experienced craftsman usually polishes 6 to 8 cases in a day.