The standards for what makes a "good watch" vary from person to person. However, some easily identifiable points include the finish and construction. In this article, we will look at the hole jewels, which are functional components but also contribute to the aesthetic appeal of the movement, to identify a good watch.
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Interview and text by Masayuki Hirota (Chronos-Japan)
[Article published in the July 2020 issue of Kronos Japan]
Identifying a "good watch" from the "holes" in the movement
The Cal. 28 boasts excellent finishing, and its hole jewels are also elaborate. Though they have little practical benefit, the rounded, three-dimensional appearance and vibrant color of the hole jewels are details unique to luxury watches. While it is now extremely difficult to obtain such hole jewels, Swiss luxury watches continue to use the finest hole jewels, following the traditions of the past. Also note the perfectly chamfered, thick screws. They have a completely different finish than mass-produced watches.
When examining a mechanical movement, the red ruby is essential as it reduces the movement's resistance. While essentially a purely functional component, like other finishes, rubies are graded according to appearance and color. The highest grade is the Mi-Glass holed stone, which has a three-dimensional shape. However, the fascinating thing about holed stones is that mass-produced holed stones are not necessarily bad.
How do you see the hole?
A dome-shaped Mi-Glass holed stone is suitable for a luxury watch. What distinguishes it from cheaper ones is that it has no flat surface on top and has a deep oil reservoir inside. Naturally, it must have a perfect mirror finish. Also, according to old standards, the color should be deep enough to resemble pigeon blood. The holed stone in this watch meets these conditions.
One of the highlights of mechanical watches is the ruby embedded in the movement. Its primary role is as a bearing to reduce resistance in the gear train, but it is divided into several grades based on appearance and finish.
Around 1890, Audemars Piguet divided the movements they produced into four grades: Extra, I, II, and III. There were ten categories, including criteria for the jewels in the holes. According to the company's documentation, the highest grade, Extra, had "balanced size, deep red color, carefully set olive-hole jewels, and carefully polished and carefully assembled bearing stones." Grade I, on the other hand, was of high quality but lighter in color than Extra, II was of good quality, and III was of good quality but fewer in number. Just like the movement finish, the jewels in the holes were also graded.
Although not completely Mi-Glass, the Cal. PF110 also has high-quality crown jewels. The top surface of the crown jewels appears flat, but they have been carefully polished to form a donut shape, as shown in the photo. What is interesting is the way the crown jewels are fixed. Like the Roman Gautier on the right page, the crown jewels are fixed slightly higher, perhaps to make it easier to adjust the gap between the gears and crown jewels. Furthermore, like the Cal. 28 above, the screws on this model have an excellent finish.
The minimum requirement for distinguishing inexpensive pins from others is whether the part that meets the tenon is rounded. This is called olive. Normally, pins in a wheel train almost never have olives, but if important parts, such as the pins supporting the balance, have olives, the resistance of the axis is greatly reduced. This is why Audemars Piguet in the 19th century specified that their extra pins were "pins for olive-beaded pins." Furthermore, even if they are artificial rubies, a vibrant red color is desirable for pins in luxury watches. This is what Philippe Dufour called "pigeon's blood" color.
With the exception of the Credor Eichi I, high-end Japanese movements have long been indifferent to the shape of the hole jewels. However, the Cal. 9SA5, released in 2020, is unusual in that it uses a partially three-dimensional hole jewel. This is the hole jewel that supports the double-barrel barrel arbor. However, it is not a Mi-Glass, but rather a hole jewel with a large oil reservoir. The flat top surface was probably left to make it easier to press the hole jewel into the bridge.
Panerai's Cal. P. 3000 has the same type of hole jewels as the Grand Seiko. The deep oil reservoir gives it a three-dimensional appearance, but the top surface is flat. Unlike those in the gear train, the hole jewels used in the barrel core do not require precise adjustment of clearance. Therefore, by pressing them in deeply, the hole jewels appear more three-dimensional. The three-dimensional effect is further emphasized by shallowly diamond-cutting the area around the hole jewels.
The grade of the hole stones is also determined by their shape. The highest quality is the Mi Glace-type hole stone, which has a three-dimensional shape. Furthermore, regardless of practical benefits, the larger the size, the better. Opinions differ on what constitutes Mi Glace, but one of the conditions is that the top surface of the hole stone is not flat, or has few flat surfaces. However, the yield rate for the three-dimensional Mi Glace hole stones is very low, and they were not widely used even before the 1960s, when labor costs were low. In fact, Jurgen Lange, who once revived H. Moser & Cie., stated, "The yield rate for Mi Glace hole stones is only 50%." Currently, major manufacturers using these hole stones include Roman Gauthier and Voutilainen.
A. Lange & Söhne uses hole jewels fixed in chatons. Nowadays, the precision of hole jewel fixing has improved, so this kind of detail is meaningless. However, Lange has always used screw-set gold chatons as an icon. Although there is no practical benefit, the chatons have the effect of making the hole jewels appear larger. The hole jewels are in the Mi-Glace style, with a slight flat surface on top. Perhaps this is to fix the hole jewels accurately.
In chronographs with multiple internal gears, the precision of the placement of the pins is more critical than in ordinary three-hand models. This is exemplified by the pins on the Cal. 01. The extremely wide top surface is intended to reduce distortion during press-fitting. This is a detail completely different from that of a luxury watch, but considering it is a practical chronograph, this choice of pins is entirely appropriate. This is an example of how three-dimensionality does not necessarily mean it is good.
In mechanical watches of a certain price range, the area around the holes that secure the jewels is always polished. Depending on the depth, there are three types: "open-cut" (degouvert), "shallow" (cruzeur), and "C-faced" where the area is only lightly machined. Movements with three-dimensional jewels have the holes processed by open-cut mining, without exception. The combination of three-dimensional jewels and a hole with a deep periphery that is dug deep gives the movement maximum visual impact. The chatons that secure the jewels, which are currently widely used by A. Lange & Söhne, are also close to the open-cut concept.
NOMOS Glashütte has the details of a well-made industrial product. Naturally, the pins are standard, with flat tops. Previously, Czech-made pins were used, but now they are made in Switzerland. Because the tops are flat, they are suitable for pressing in by machine. In fact, NOMOS now basically presses in most of its pins using automatic machines. Although there are some negative opinions about flat pins, they do increase the precision of the pin placement.
A basic model equipped with the company's own Cal. α movement. The basic design dates back to the Peuzeau 7001 from the 1960s, but the use of Triovis regulator and other features gives it chronometer-level precision. The calfskin strap is a plant-dyed "Sophora japonica" design. Manual winding (Cal. α). 17 jewels. 21,600 vph. Power reserve of approximately 43 hours. Stainless steel case (35mm diameter). Water resistant to 3 bar. Limited to 60 pieces in Japan. 260,000 yen (tax included). (Inquiries) Osawa Shokai Tel. 03-3527-2682
In cheaper movements, the shape of the hole jewels is flat. Also, the processing around the holes is a lightly roughened C-shaped groove. However, flat hole jewels are not necessarily bad. They make it easier to apply uniform pressure and therefore easier to press precisely into the base plate and bridges. For this reason, the majority of mass-produced movements have flat hole jewels. In recent years, an increasing number of mass-production manufacturers have begun to set hole jewels automatically, but this is also possible only because of flat hole jewels.
Although today's Unitas watches have a completely modern appearance, some details still resemble those of traditional pocket watches. The most obvious example is the second wheel's hole jewel, which has an extremely large oil reservoir. While the movement design has been modernized, this detail has likely remained unchanged for decades. In the days when the quality of oil was poor, it was common for the hole jewel in areas subject to heavy loads to have a large oil reservoir.
This hand-wound model was released to commemorate the 165th anniversary of the company's founding. It is equipped with the classic "Unitas" ETA6498 movement. The grained dial also adds to its classical charm. The price of 110,000 yen is also very attractive. Hand-wound (Cal. ETA6498-1). 17 jewels. 18,000 vph. Power reserve of approximately 46 hours. Stainless steel case (diameter 42mm, thickness 11.35mm). Water resistant to 5 bar. 110,000 yen (tax included). (Inquiries) Tissot Tel. 03-6427-0366
How to identify hole stones
An example of a holed stone that reduces resistance to the shaft. In reality, all holed stones have an "oil reservoir" that is a depression for storing oil. However, this has been omitted for clarity.
❶ is a standard flat stone. In addition to its flat shape, the surface that comes into contact with the axis is often flat. Therefore, there is a lot of resistance when the tenon and the hole stone come into contact.
❷ is found in high-end balance instruments. It uses an olive with rounded sides. The contact area with the shaft is small, which greatly reduces resistance.
And ❸ is Mi-Glass, which has a dome-shaped top surface. The raised top surface creates a visual effect. These types of hole stones often have a bright red color.
❹ shows the balance shaft and its hole stone. The large depression on the inside is an oil reservoir. If the balance shaft is conical as shown in the figure and the hole stone is an olive, the position error will be small.
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