Looking at the dial or back cover of a mechanical watch, you probably noticed the inscription 17 Jewels Or a picture of seven rubies. For most people, this is just a decorative element, indicating belonging to the classics of watchmaking. However, behind this figure lies a complex engineering system that ensures the accuracy and durability of the mechanism.
In today’s world, where quartz technologies and smart gadgets dominate, mechanics remains the benchmark of prestige and engineering thought. Understanding what these stones mean will help you distinguish a quality mechanism from a cheap consumer product. Rubies In the watches are not just jewelry, but functional parts that work in extreme conditions.
Why seventeen? The answer lies in the design of the mechanism itself and the number of friction points that require protection. In this article, we will take a closer look at the physics of the process, the history of the introduction of synthetic stones, and explain why the presence of 17 stones is often the “gold standard” for basic mechanical calibres.
Historical background and evolution of stone use
The history of the use of precious stones in watchmaking goes back to the XVIII century. Then watchmakers noticed that the steel axes of gears wear out quickly, grinding the brass platinum mechanism. Nicolas Fatio de Duillet The first proposed to use natural rubies and sapphires as supports for axles. These materials had incredible hardness and low friction coefficient.
For a long time, the use of natural stones made watches a luxury item, accessible only to the aristocracy. The situation changed dramatically in the early XX century, when Swiss engineers developed the technology of synthesizing rubies. This allowed for mass production. mechanical-calibre with high wear resistance at an affordable price.
By the middle of the XX century, the number of stones became a marker of quality. If in simple alarm clocks there were 7 or 15, then in expensive pocket and wrist models the score went to dozens. It was during this period that the 17-stone standard was formed, which provided full protection for all critical nodes of a simple mechanism without central combat or autowinding.
Pay attention to the color of the stones: in quality mechanisms they have a rich purple hue, and in cheap fakes can be simply painted with paint on platinum.
Friction Physics: Why a Mechanism Needs Rubies
The main task of stones in the clock is to minimize friction in places of rotation of the axes of the gears. The mechanism consists of many wheels that must rotate with great speed and minimal resistance. If you use a conventional pair of “brass steel”, the friction coefficient will be high, which will lead to rapid wear and loss of power reserve.
Synthetic ruby (aluminum oxide) has a hardness of 9 on the Moore scale, second only to diamond. The surface of the stone is polished to perfect smoothness, which, combined with a drop of special watch oil, creates conditions close to perfect slip. Material hardness It ensures that the axis does not wipe itself “pouche” even after ten years of operation.
In addition, the stones have low adhesion to the oil. The oil does not spread over the ruby surface, but is held in the center due to the forces of surface tension, forming a stable lubricating lens. This is critical to maintaining oscillation balance throughout the period between the spring plants.
- 💎 Reduced wear: The stone takes the main load, protecting the softer steel axes.
- ⚙️ Stability of stroke: Minimal friction ensures uniform transfer of energy from spring to descent.
- 🛡️ Protection against corrosion: Synthetic stones are chemically inert and are not susceptible to oxidation, unlike metals.
Why rubies?
Although sapphires are harder, rubies have an optimal combination of hardness and the ability to hold a microscopic drop of oil due to their crystalline structure.
Decoding the Number 17: The Anatomy of the Mechanism
Why 17? This figure is not taken from the ceiling, it is due to the minimum number of support points necessary for the full operation of the mechanism with the second hand and the central balance. Let’s look at where these 17 stones are in the standard caliber.
First of all, the stones are installed on the axis of balance - the fastest and most important node. It is usually used 2 stones (bearings) and 2 stones on the linings (total 4). Next are the stones on the anchor fork and balance wheel (angrenage), ensuring the operation of the trigger mechanism. The remaining stones are distributed along the wheels of angrenage (central, intermediate, second).
It is important to understand that the number of stones depends on the design. Mechanisms without a second hand (a small second on a separate dial) may have fewer stones. The presence of 17 stones indicates that the mechanism is equipped with full protection of all rotating axes, including the axis of the second wheel, which is a sign of the movement. qualitative basic mechanism.
| Mechanical assembly | Number of stones | Function |
|---|---|---|
| Balance (axis) | 2 | Support for the balance axis |
| Balance (overlays) | 2 | Fixing and protection against axial backlash |
| anchor-fork | 2-3 | Transfer of momentum to balance |
| A second wheel. | 2 | Second-hand axis support |
| Angrenage wheels | Others | Spin transmission |
Difference between 17, 21 and 25 stones
If 17 stones is good, why are there 21, 23 or even 25 stone mechanisms? The increase in the number of stones is not always directly proportional to the quality or price of the watch. This is often due to the presence of additional features such as autowinding or calendar.
21 stone mechanisms usually have additional protection for autowinding wheels or a more complex descent design. Stones can be added to intermediate wheels of angrenage, which theoretically reduces wear, but in practice the difference in durability between 17 and 21 stones in household use is minimal. Excessive number of stones It is sometimes used by marketers to increase the perceived value of a product.
There are also the concepts of “functional” and “decorative” stones. In high-quality Swiss and Japanese calibres, each stone has an engineering justification. In cheap Chinese copies, you can find mechanisms with 40+ stones, where half of them are simply glued to platinum for beauty and do not carry any functional load. That's why. 17 Functional Stones They are often valued higher than 40 decorative ones.
⚠️ Warning: High stone counts (over 25) in cheap watches by unknown brands are often a sign of marketing ploy. The real value is determined by the quality of stone processing and assembly accuracy, not by the quantity.
The number of stones makes sense only up to a certain limit; after 21 stones, the increase in reliability becomes negligible without the introduction of complex functions.
Synthetics against straight people: modern realities
Today, you won’t find a mechanical watch with natural rubies unless it’s an antique or an exclusive art object worth millions of dollars. All modern. 17 Jewels These are synthetic corundums grown in laboratories by the Wernail method. Chemically and physically, they are identical to natural analogues, but free of defects and cost thousands of times cheaper.
The use of synthetics has allowed the standardization of production. Each stone has perfectly predictable properties of hardness and roughness. This gives watchmakers the assurance that the mechanism assembled today will work just like the mechanism assembled a decade ago. For the watch owner, this means predictability in maintenance and maintainability.
Interestingly, some luxury models still use terminology hinting at the jewel, but legally they are required to indicate the origin of the stones. If it says on the clock Synthetic Ruby plainly Jewels This is standard modern mechanics. Natural inserts are found only in jewelry watches, where the stones do not come into contact with rubbing parts of the mechanism.
☑️ What to look for when buying used mechanics
Maintenance and signs of stone wear
Despite the high hardness, stones in the clock also require care. The main problem is not the wear of the ruby itself, but the drying or contamination of the oil in the bearing. If the oil is converted into a thick substance, the friction increases and the clock begins to lag or stop. Regular lubrication (every 3-5 years) is necessary to maintain the operation of the stone-axis system.
In rare cases, usually after a heavy blow, the stone may crack or fall out. The use of a watch with a damaged stone is strictly prohibited. The wheel axis, devoid of support, will instantly wipe the brass platinum, which will lead to expensive repairs of the entire mechanism, comparable to the cost of a new watch.
Signs of problems with stones can be:
- 📉 Unstable move: The clock is in a hurry, then lags behind during the day.
- 🔊 Extraneous noise: Screaming or grinding inside the body when shaken.
- 🛑 Stop: The mechanism stands up even if the spring is completely closed.
⚠️ Warning: Never try to lubricate the mechanism yourself through Caseback unless you are a professional. Getting oil on the balance or hair of the spiral will lead to a complete stop of the clock and require ultrasonic cleaning.
The influence of the number of stones on the price and collectible value
In the world of collecting stones, the number of stones plays a secondary role compared to brand, history and fortune. However, for the mass market of the middle of the XX century there was a clear gradation. A 17-stone watch was considered a mechanical watch. Models with 7 or 15 stones were in the budget segment and often did not have the protection of the second wheel.
Today, there is a marking. 17 Jewels on vintage watches of Soviet or Swiss production (for example, Poljot, Vostok, Tissot) indicates that the full calibre is installed inside, not a simplified version. This makes these products more liquid in the secondary market. Collectors value “honest” mechanics, where each element is justified constructively.
In conclusion, it is worth noting that the magic of a mechanical watch is not the number of stones, but the harmony of their interaction. 17 stones is an engineering minimum, turning a set of gears into a time meter. Understanding this helps to appreciate the work of watchmakers and take care of the mechanism that ticks on your wrist.
The 25 Stone Myth
There is a myth that a watch with 25 stones is more accurate. In fact, accuracy is regulated by the quality of the balance and hairspring, and the extra stones only prolong the life of the mechanism with complications.
Can I replace the stone on my own?
This is not possible without professional equipment. Installation of the stone requires precision pressing under the microscope with respect to micron tolerances. An attempt to glue the stone with glue will lead to the destruction of the mechanism.
Does 17 stones mean the clock is waterproof?
Absolutely not. The number of stones refers only to the internal mechanism (caliber). Water resistance depends on the design of the case, sealing rings and glass, which is not related to the number of rubies.
Are synthetic stones really worse than natural stones?
In the context of the clockwork, no. Synthetic rubies are cleaner, more uniform and cheaper. Natural stones would have microcracks and inclusions, which would degrade their frictional properties.
How often should the oil in the stones be changed?
The recommended maintenance interval (TO) for mechanical watches is 3-5 years. During this time, the oil oxidizes and loses its properties, which can lead to wear and tear of the stone-axis pair.