Time through the glass

Watch of a modern man, trying to keep up with the elusive time, is a thing that "follows" him, no matter where the owner goes: to work, for a walk, to the pool, fitness room, etc. Therefore, in addition to the aesthetic function our watches bear, the time meters should be reliable and durable, able to resist the influence of magnetic fields or go through sudden changes in temperature. But sometimes your wrist time "assistant" might fail even because of the slightest trifle, such as getting the tiniest speck of dust or moisture inside the case. All this is a matter of chance. To avoid such trouble, and for some fans of watches - a terrible tragedy, the watchmakers try to make the watch case as tight as possible. High tightness is achieved by the main case part of a watch, the bezel, and, of course, the dial glass, and if the back case is transparent, then the back case too. Referring to the opinion of famous Russian watchmaker Konstantin Chaykin, I should note that the glass of wrist watches has an important protective role. The craftsman from Petersburg explains that the watch glass also serves to protect the hands from mechanical impacts, scratches, abrasions, etc. Of course, Konstantin Chaykin does not recommend to take the words "ultra-solid glass" literally, since the glass of any strength cannot withstand strong impacts. No wonder, the glass is always glass!
The words of pragmatic Chaykin are undoubtedly true, but I'd like to add that the glass, covering the dial or replacing the back case, possesses a special philosophical hidden motive. The infinite and great time is indicated on the dial, but it comes down to us only after passing a kind of "glass test". It means that for the owner of watch the glass is a mediator, "ambassador" of the almighty time, so to say. It turns out that watches always show us the current hour, minute and second through the amazing "time" glass. The mystery of glass used in various spheres of human life is also confirmed by some legends about the appearance of this irreplaceable material.

Legends

Today, thanks to the amazing archaeological finds, we know that the first glass was created by human hands in the 35th century BC. The researchers have found a light green glass bead of 9 mm x 5 mm size (how could it be noticed at all?) near the town of Thebes. We are talking about a man-made glass indeed, because the natural glass, appeared from fusion of rock during the eruption of a volcano or in any other thermal effect, was discovered by ancient people long before that. Returning to the legends about the appearance of glass, we should say that the man-made glass was discovered completely by chance, as a byproduct of other activities. I am always amazed by the fact that everything genius and necessary was invented suddenly. Let’s remember Newton and his apple or Archimedes, who took a bath. However - the glass.
The first legend says that the glass was obtained by the craftsmen, who were engaged in manufacturing of clay items. In ancient times such products were fired in ordinary pits, dug in the sand, and the straw or reed was used as a fuel. The combustion of fuel resulted in ash, which, as it was known, at a long time infusion on the water made lye. The material obtained by heating and contact with the sand (luckily it was quite enough in the pits) formed a glassy mass.
Some historians say that the glass was obtained by man during the melting of copper. Without going into details of chemical reactions and phenomena, I will say that the glass is one of the byproducts obtained in the process of copper melting at high temperatures.
The most popular legend of the glass is the "story" about Phoenician sea merchants told by the Roman historian Pliny the Elder (79 - 23 BC). According to this source, a ship, carrying soda to Phoenicia from Egypt, was stranded to the river Belous (Levantine coast, Phoenicia). The pressed pieces of soda were got out from the water by merchants, who had not found any rocks nearby to build their hearth and cook a food. Finally, the traders used the means at hand and made the furnace of soda, which at high temperatures mixed with sand. I can imagine how surprised the hungry traders were, when they saw the incredible translucent streams of liquid flowing from the furnace and solidifying on the ground! The merchants did not even suspect that many centuries later the material obtained by them by chance would decorate and protect our watches.

Facts

Perhaps, the reader will find me cruel, but nevertheless, I’ll break down the beautiful myth of Phoenician merchants-discoverers. If we analyze the historical data correctly, we’ll get the following conclusion: the story of Pliny the Elder is a reflection of Roman glass production experience, started in the I century BC. I hope that our readers are not going to repeat the experiment with soda and sand, because, unfortunately, nothing will be obtained. Empirically it is proved that in such a way that was described in the legend, it is impossible to make glass – an extremely high temperature, which cannot be provided by any, even the biggest bonfire, is required,. In addition, there are other technological features, which contradict this version of artificial glass appearance.
It is believed that the glass craft arose in ancient Egypt in about III century BC, as most of the glassware was discovered at that area. Of course, the glass items could be brought to Egypt from anywhere else. Glass was an object of luxury, and the same legendary soda, obtained from wood coals, was used for its production. Over time, the glass and articles of it (vessels, vases, beads, etc.) spread outside of Egypt. The first direction in the form of a table with instructions how to make the glass belongs to 650 BC: it was found in the library of the Assyrian ruler Ashurbanipal. Let the legend of Pliny about the origin of the glass be considered a myth due to its unreality, however, reviewing various sources, I have not found a correct story about the appearance of glass from the science point of view. Who was the first master and how he thought to warm soda and sand remained a mystery for me. Science can answer: the existence of natural glass prompted man to create its artificial counterpart. Well, let it be so. Or, maybe, the Phoenician merchants are not so fictional characters? Everybody holds his point of view, but agree that both women's and men's watches without glass are something out of the ordinary. If the dial is a "face" of the watch, as the connoisseurs of horology like to say, we can say that the glass is a "make-up" of the dial. And the appearance of wrist time meters depends on the quality of make-up. Here is more information about the technique of application and types of "watch make-up".

Without glass

Before we begin to study the types of glass, protecting the dial of a wristwatch, let’s pay attention to the certain, special kind of time meters. Earlier I’ve mentioned that a watch without glass is not a watch anymore. However, there are models that are deliberately deprived by the watchmakers of transparent "make-up". Today, one of the leading companies producing watches for disabled people is the Swiss watch company “Auguste Reymond”, which releases these watches under the brand name “ARSA”. However, the glass in these watches is still present – the owner of the watch needs to discard the glass cover and pass his fingers on the convex watch markings to determine the current time. At the age of mechanization and development of computer technologies such wristwatches are gradually replaced by more convenient electronics, which "says" the time to the owner after clicking on a button on the case. In addition, for the visually impaired and blind people the models of watches, the dial of which includes Braille, are comfortable (accordingly, these are wristwatches without glasses). Watches for disabled people can also be found in the collections of watch companies, like Swatch, Seiko, TokyoFlash (watches with built-in microvibrators) and others. Another option – albeit very expensive, but truly majestic and legendary – is a mechanical wristwatch with repeaters, from the notes of which current hour and minute are composed. Generally, the glass in the watch industry was used centuries ago, when the first "pocket brothers" of today's wrist watches, equipped with glasses from rock crystal, appeared. Now this material is rarely used, and the watchmakers replace it with the following types of glass: plastic (plexiglass or hesalite), mineral and sapphire glasses. Interestingly, the models with different types of glasses are in totally different price ranges on the market. The type and quality of glass affect the price of the good in the same way as the number and technical level of complication, placed in a watch. So, take a look at "different" time through the different types of glasses.

Plastic

Plastic in the watch industry is also known as organic glass, plexiglass or hesalite, made from industrial kinds of silica glass. Among the advantages of plastic the feature to easily take a variety of complex geometric shapes that are suitable for any kind of dial and any form of case should be noted especially. Despite its softness and plasticity, plexiglass has a quite high rate of impact strength due to its fibrous structure (though this, of course, depends on the type of plastic). The watches with this type of protective glass are preferred by most athletes and people, who lead a very active lifestyle, as for sport events and training the plastic is practical enough. As a consequence of the aforesaid, at the global watch market there is a large number of watches and chronographs in sport style, equipped with plastic apertures, and the case of these watches is also often made of plastic. Among the "plastic fans" there are the watch companies “Casio”, “Swatch”, “Sector”, “Swiss Military”, “Timex”, “Lowell”, and others. Another indisputable advantage of this material is its accessibility, as it compares favorably from other types of glasses of low cost. But nothing in this world is perfect, and the plastic glass is so much the more. So, at frequent contact with other materials and surfaces the plastic is easily scratched. The scratches appear even if you wear a shirt of coarse cloth, a sleeve of which constantly touches your watch. As a result of appearing numerous scratches such glass gets cloudy that reduces the degree of readability of the dial, and eventually the plexiglass also turns yellow. However, everything isn’t as bad as it seems at first sight, because if you want you can give the plastic glass to a watchmaker, who can easily polish it, since it is not so laborious process. Sometimes the polishing of organic glass is not quite effective, especially if the scratches are very deep. In this case, the plastic glass should be replaced without hesitation.

Mineral glass

Mineral (or silicate) glass - it is an artificially grown mineral of quartz, and by its main features this glass is similar to usual window glass. Mineral glass, which is sometimes metaphorically named "rock crystal", is the most common type of glass not only for watches, but also for the things, used in various spheres of human life. Until recently, mineral glass was a standard even for the most expensive and luxury Swiss watches. And on this day, mineral glass adorns 90% of watches all over the world, moreover, it is used by almost all companies, from giant Swiss “Rolex” and ending with a small German watch company “Minister”. Mineral glass is advantageous by the fact that this type of protective "make-up" of dial, as compared to plastic, has a greater hardness and is more resistant to scratches and abrasions. Nevertheless, mineral glass can be easily scratched with a metal object or a stone. Of course, this type of glass, as well as plexiglass, can be polished at the nearest watch workshop or replaced, previously selecting a glass of required form, fortunately, it is now issued in a huge range. The savvy PR experts invented for that watch glass the name "crystal" and indicate it on the case as “Crystal (glass)” to increase the popularity of the product. Therefore, if the owner of the watch tells you with some degree of importance "I have a crystal on my watch!", you shouldn’t take this remark literally. Well, the clever marketing experts have managed to cheat the credulous public once again, as crystal glass is a very rare phenomenon in today's watch world. Since I have already started talking about crystal, already become a thing of watch history, I’ll note that crystal glasses excelled the materials described above by their quality, but did not differ from plastic on the degree of scratch-resistance.
The disadvantage of mineral glass is relatively low degree of strength even after hardening (compared with plastic), but there are so-called mineral glasses of high strength. The watchmakers apply a special hard coating on them, resistant to mechanical damages. But let’s remember the advice of Chaykin not to beat the watch glass with fist or other hard objects, no matter what strength your manufacturing company guarantees. Comparing plastic glass with mineral, it is worth to clarify that mineral glass will keep transparency longer than plastic, although even this type of glass might eventually fade slightly. Mineral glass is mainly placed into the watch cases of medium price range at the world market. For example, the silicate glasses are provided in Japanese watches of Casio, G-Shock, Italian watches of Gaga Milano, Swiss watches of Tissot, and others.

Sapphire

Another type of glass, used by the masters of watchmaking, is sapphire. The name sounds beautiful, proud and expensive. No wonder, since sapphire is beautiful, proud and very expensive. But it is should be kept in mind that this term is conditional in some way. The wristwatches are provided with artificially grown sapphire, which, however, has the main characteristics of true crystal - high hardness (please do not confuse with strength) and transparency. Sapphire crystal is obtained after high-temperature processing of crystallized aluminum oxide Al2O3. For the first time in the watch industry they began to insert sapphire crystal in the watch case in the mid-60s of the XX century (it is interesting that the artificial sapphire was obtained earlier, in 1904). These glasses now occupy a dominant position in the production of wristwatches of the highest (and average) price range. One has only to hear the names of world -known watch brands, which use sapphire in their works, as it becomes clear that this is a surprisingly good and worthy material for high-quality watches. The men’s watches from the collections of Italian watch companies “Anonimo”, “Panerai”, the Swiss watches from “Rolex”, “Azimuth”, “Patek Philippe”, “Vacheron Constantin”, and many others shine with sapphire plays and eye-catching splendor. Due to high transparency sapphire ensures perfect readability of the dial. Sapphire is practically impossible to scratch in domestic environment, so it never ages and retains its luxurious luster throughout the "life" (of course, with proper care of the glass). Over time, the case and the strap (or bracelet) of your favorite watch might even become rather shabby, but sapphire glass will sparkle like brand-new. However, even sapphire is not perfect, it can be scratched, only with a diamond though (for example, a ring with a big gem, or even an ordinary diamond nail file) because of the highest hardness of the latter (compare the hardness of sapphire - 9 points by the Moos scale, of diamond - 10 points). Other man-made materials containing silicon carbide and with an intermediate hardness by the Moos scale (between the sapphire, 9, and diamond, 10), also might cause scratches on the precious glass. In modern industry, such "dangerous" materials for sapphire are sometimes used in the manufacture of furniture and decorative wall coverings. So you shouldn’t think you may hit and scratch your watch, if its dial is provided with sapphire crystal.
Just like you cannot kill two birds with one stone, you cannot "catch up" hardness and strength of sapphire simultaneously. Although this glass is very hard (therefore, it isn’t scratched), but it is not so strong, and sometimes it is broken even easier than the above mentioned "glassy" materials. Well, it’s quite natural, since any expensive, beautiful thing needs the most careful treatment. The high cost of sapphire is caused not only by its excellent features and characteristics, but also high complexity of processing the material, as creating various forms of sapphire, for example, rectangular, barrel-shaped, heart-shaped, etc., as well as cutting is a laborious process even for the most experienced craftsmen. While manufacturing sapphire protective glasses for watches, or the so-called boules, they are cut by special diamond saw blades into disks, which are then grinded to required size and polished. As we can guess, the tools for such work are not cheap - hence the high price of a watch with sapphire glass. The advantage of sapphire and mineral glasses is a high moisture protection that they offer thanks to inserted special washers between case and glass. Thus, men's wrist watches with high water resistance simply must have a sapphire crystal, or, at worst, a mineral. It should be noted that some manufacturers do not install sapphire on the men's watches for divers, since this material might not cope with the high static pressure due to its hardness (and therefore, according to the law of physics, fragility).
It is known that the natural sapphire, used in the jewelry industry, is a variation of blue corundum, but, unfortunately, the artificial sapphire cannot be composed of substances that are responsible for imparting different shades of this glass.

What is the truth?

And now, dear reader, I would like to ask you to digress for a few minutes and pay attention to one of frequent questions, which is of interest to all fans of quality watches: "How to distinguish sapphire from mineral glass?". The point is that these two glasses are so similar by appearance that it’s almost impossible to find any difference, so a gullible and ignorant customer when buying a wristwatch might face fraud. Although the buyer himself might be wrong informed. You can, of course, find the inscription “Sapphire crystal” on the case of the model you like. This greatly simplifies the task. Well, what else can we do if such marking is missing, and we don’t want to believe the seller on the say-so? The experts advise using "materials at hand", namely your nose. If you touch by the tip of your nose alternately sapphire and mineral glass, you’ll feel that sapphire is cooler than mineral glass. In addition, sapphire crystal stays cool for longer, i.e. it is heated much more slowly. From the first time it is quite difficult to understand, you’d better to train in advance. Of course, this method does not give absolutely correct results, since some facts should be considered. For example, if a watch for some time was worn on a wrist, then the glass of this watch will be warmer anyway, regardless of the glass type.
If you still do not want to freeze your nose, then there is another way - "water procedures". You may drip water on the glass, but previously wash the surface, cleaning the stains. Then you watch. The drop of water starts to spill at the mineral glass, and at the sapphire it is like a drop of mercury. It will not spread and will move "without a tail". However, there is a catch – at the glass with anti-glare coating (if the outside is coated) the drop will not move, but stick to the glass surface.

Finally, for extreme sports lovers, who like to tickle themselves, there is another way to recognize the sapphire, fairly dangerous for the "health" of watch. Before going to the store take a nail or a box of matches. Well, the truth is worth the risk! When the seller starts assuring you that the watch he shows has sapphire crystal, take out the nail imperturbably and ask the seller to try to scratch the material. It is known that nothing will happen to sapphire, unlike the mineral glass, which will get a scratch. If the seller gets nervous and refuses to do such a dangerous operation, do not hurry to choose the model. A burning match is also a pretty effective way to test the strength of the glass. Thus, at the time of head ignition the sapphire crystal won’t have any significant traces, but on the mineral surface you'll notice a little smoke, well, the plastic, of course, will melt. Considering the above methods of testing, I'm not talking about the glasses of watches with different coatings and sputtering. If you are trying to scratch an anti-glare sapphire, the coating will certainly be damaged. It should also be taken into account if you want to know the truth about the dial glass.
It only should be added that every fan or collector of watches is guided only by his experience, his tastes and preferences when choosing a model. Each of two types of glass, both sapphire and mineral, has its pluses and minuses. So there are, at least, two truths here. For someone it is principle to have a glass without a single slightest scratch. But someone is ready to give his "ticking treasure" into caring hands of a watchmaker for polishing or replacing the glass. In any case, it’s up to you.

Combined glass

Go back to the types of dial glass. In addition to above types of watch glasses, there are other options to protect the dial, or, say, the combined types of glasses. The experts, chemists and physicists worked hard to create variants of protective glasses that combine all the benefits of its mineral and sapphire "colleagues", resulting in quite high degree of strength and resistance to all sorts of scratches and mechanical damages of combined glass. Combined protective glass may be considered as the most democratic option of expensive sapphire glass. On the one hand, it is clear – there is no need to pay more if the properties and appearance are practically indistinguishable from brilliant sapphire. However, for some people the mere fact that their watches are equipped with a sapphire crystal is extremely important. For example, the combined types include the so-called glass “Sapflex”. This is a two-layer glass that is mineral glass with sapphire coating. Here you are - both durable and less scratched, but, alas, not sapphire. A striking example of models with Sapflex is the men's and women's watches from the Japanese company “Seiko”. And another kind of combined glass is Hardlex, the same mineral glass, unrecognizable "in the make-up". It undergoes a special treatment to increase the rate of strength, and it is marked "ultra-strong" for greater importance. For example, the Japanese watches “Seiko”, “Pulsar”, “Lorus” have this type of glass. The strengthened mineral glass “Hardlex” is characterized by a rather high rate of hardness - about 7 points by the Moos scale, but it is far from sapphire (9 points). The disadvantages of Hardlex lie in the fact that it is scratched easier than sapphire, but it is less likely to be broken, so ultra-strong mineral is often set in men's diver watches, where functionality is much more important than aesthetic beauty.
I must add that there is no simple answer to the question "Which of these four types of glasses is better?" The connoisseurs of watchmaking don’t advise to refuse the model you like only because, for example, it doesn’t have a sapphire, but an organic glass or silica. As we’ve found out, sapphire is not perfect either. Another glass feature, to which the watchmakers draw the attention of their customers, is that you should not replace one type of glass by another. Since watch is not a car, tuning is hardly appropriate.

"Factory tuning" of glass

Dial glasses are a wide field of activity for the most talented designers, engineers and highly skilled watchmakers, who keep on self-developing. Sometimes the dials of complex watches are too loaded with various counters, indices, hands and so on, so it’s simply impossible to place a big date indicator on it. In this case, the designers resort to a rather good solution: they place a special spherical lens on a flat glass, which visually increases the date aperture. The Swiss watches from Rolex (for example, the model “Rolex Day-Date II”, or the men's watch “Rolex Submariner”) differ by such interesting technical feature, as well as the Swiss watches by Chopard (look, for example, at the men’s watch “Chopard Gran Turismo XL Alfa Romeo”) and Italian watches of Anonimo (the collection “Anonimo Militare”) have such "enlarged" aperture with the date.
Also, due to loaded dials the watch companies sometimes put their company’s logo in the form of laser engraving or pad printing on the inside of the glass. It seems that the logo is just hovering over the hour markers and indices and unobtrusively makes itself seen as in the luxury wristwatches from the Russian company “Tserdo” (for example, the men's wristwatch “Tserdo Autumn”).
In watchmaking there is such a notion as a "mask" of glass. It represents an amalgam (a solution, coating) of silver, gold, black and other colors. "Mask" is unique, as it makes the so-called ledge between glass and case invisible, and thus gives the model an unusual image. This interesting design decision is adopted by the Swiss watch company.
The above-mentioned Swiss watchmaker “Chopard”, a genius in the field of diamonds, offered an amazing and incredibly beautiful design element relating to the dial glass. These are so-called "floating diamond": a special case with two sapphire glasses, between which the diamonds were moving freely, was designed. A mere movement of hand makes the gems move, they "live" their own lives under a dome of transparent sapphire glass. This original idea is embodied in the collections of the Swiss watches “Happy Diamonds” and “Happy Sport” by Chopard.
As for the glasses of models with digital time display, they are often provided with luminescence, special sensors, which turn on the features of thermometer, altimeter, barometer, stopwatch and many others. Original and convenient - one cannot argue with that.
The world-famous Swiss watch manufacturers often apply anti-glare coating on the inner (and sometimes on the outer) side of the mineral or sapphire glass, which improves the dial readability several times. The specialists cover the glass with thin film, which is also quite common in the production of anti-glare glasses, various optics, lens of photo and video cameras. The anti-glare (or anti-reflex) coating plays an important role in watchmaking too, as this film reduces the ability of glasses to reflect the light directed at them, that is to glare, thereby improving the readability of the indications. Anti-reflective coating is most commonly used when creating aviation, diving, sports watches and chronographs, in which the readability of information is incredibly important. Since anti-glare makes no reflections, then it seems that the dial is deprived of the protective glass at all. You might notice a faint purple or blue tint of the glass, observing it at a large angle (the tint is seen best of all if the watch has a white dial). The anti-reflective coating also increases the transparency of the glass by 8-10%. However, as it was mentioned above, a rather expensive glass with anti-reflective coating (even Sapphire) might get scratched with time, but the scratches remain only at the coating. Thus, the experts from the Swiss watch company “Tag Heuer” posted on the official website an appeal to the owners of luxury watches, which calls to treat the time meters with maximum care, as "such coating (anti-glare) can be easily obliterated in close contact with the hard and rough surfaces." Often, the owners of watches with anti-glare glasses complain about a short life of the coating. However, the number of supporters of anti-glare is also great. I believe that we need to be aware of both advantages and disadvantages of the cover and only then make a decisive choice. I hope I have helped you to understand the pros and cons of this or that material.

Forms of glasses

In watchmaking, there are several forms of protective watch glass. Let’s consider the most common forms in order, from simple to complex. According to the simplest classification, all glasses are divided into round and figured. The round ones are clear, and the figured glasses include square, oval, diamond, medullary, and many other types of glasses. It is easy to guess that the shape of the glass depends on the type of a time meter and the shape of a wristwatch’s case. Figured glasses are found in original design wrist watches. The form of figured glass is made by a mold of a watch case with quick-drying two-component plastic. For the sport models round, rectangular or square glasses are specific. Strict men's wristwatches in military style are ascetic and simple in all elements, including the shape of the glass. Such watches are characterized with round glasses (for example, the Italian men's wristwatches from Anonimo). The most unique and exclusive are figured sapphire glasses, due to high complexity of artificial sapphire treatment. Nevertheless, the watchmakers are not looking for easy ways and give sapphire different figured shapes.
To maintain uniformity, the watchmakers use the conventional notation of different types of glasses. The most common are the following forms:
1. lunette - a round glass (in French - "full moon").
2. shaped crystal - any figured glass, i.e. a glass of non-round shape (e.g., oval, rectangular, square, barrel-shaped, etc.)
3. cocktail - the most exclusive and exotic forms of glasses, that is more complex performed variations of figured glass (shaped crystal), which include glasses in the form of elongated baguette, octagons, etc.
4. bombe, boule, cheve - quite rare concave glasses.
5. raised crystal - a very interesting form of glass. When viewed from above, the glass is flat, but slightly elevated at the same time. This shape resembles a cake.
There is another classification of wrist watch glasses, according to which the glasses are divided into flat (flat crystal) and convex options (domed crystal). The most common and easy to manufacture are flat glasses of dials. When damaged such protective glasses are easiest to be replaced because they are often sold ready-made, one will only have to select the appropriate diameter and thickness. For example, the men's diver watches must have glasses of at least 2-millimeter thickness. The convex form of the glass is more complicated in performance. This glass usually has large sizes, so due to its practicality and strength it is set on sport watches. An arched form of convex glass creates an effect of lens and visually enlarges hour indexes and indices.
Protective glasses of watches, like all glasses in the world today, are influenced by fashion, since the glass is one of the most notable parts of watches. Therefore, the "makeup" of the dial must be necessarily performed according to the latest fashion. Before the convex types of glasses were popular, then - the flat forms. The cut glasses were in fashion in 1970s. If you look at the situation in recent times, you can see that the glasses, exactly duplicating the shape of the watch cases, not only along the contour, but in the profiles too, are most popular.
Sure, the glass dial is a very important element of any model of watch. It is responsible not only for the safety of the movement and dial, but also for the attractive appearance of time meter. The aesthetic function of dial’s "makeup" plays an important role, as because of scratched glasses the watches lose their charm and grandeur. Therefore, it is necessary to take care of the "transparent make-up" of your time meter for it kept its original form and did not break down in any case. But if the worst has happened, do not panic. Look positively at the world – as glass breaks for luck!

Glass thickness

Speaking of wristwatch glasses, you should pay special attention to such important characteristic of transparent "defender", as its thickness. Earlier I said about degree of strength and shock resistance of each type of the watch glass, but it's absolutely pointless to judge these characteristics, without taking into account the thickness of glass. If we remember the predecessors of wrist time meters, pocket watches, we can see that the average thickness of glass in such models was incredibly small, it made up only 0.5 mm. Of course, the folding steel cover served as an additional protection in pocket watches. With the development of watchmaking a more convenient variant of time meter – wristwatch, safety glasses of which have noticeably "grown fat" – has become widely spread. Thus, the standard thickness of modern watches’ glass ranges from 0.8 mm to 1.2 mm. In principle, it is quite enough if you're not going to expose your watch to various tests, and plan to use it in everyday life as a time meter.
The men's wristwatches with protective glasses of thickness exceeding 1,2 mm are mostly designed for diving, that is watches used by professional divers, submerging into water at a certain depth. In this case, the "life" of watches depends on the thickness of the glass. The men's watches for scuba diving have glasses of 4-mm thickness, and sometimes even more. However, besides the thickness of the glass, its form also plays an important role. For example, the glasses of convex shape better transfer, that is distribute, the pressure on its surface. Therefore, most often the diver's watches are provided with convex glasses (of course, the thicker the better). As you know, if we compare the degree of impact resistance of mineral and sapphire glasses, then the first one wins. Yes, Sapphire breaks easier, but its great advantage is that it isn’t almost scratched. Studied in detail the laws of physics on hardness and strength of glasses, many watch companies choose mineral glass for the production of diving watches. It is logical. However, such glass might lose its original appearance because of numerous scratches after a few dives. Glass might easily get scratched on the reefs. With the sapphire everything is quite the opposite. Despite the common belief that the sapphire is not suitable for diving watches, the masters decide the issue by increasing the thickness of the glass. It turns out that sapphire glass is ideal for divers. It provides perfect readability of dial (in combination with anti-reflective coating), it isn’t practically scratched, and it is able to withstand great pressure, having a thickness over 1.2 mm.
Many world-famous watch companies manufacture diver’s watches. So, the Italian watchmaker “Anonimo”, born in beautiful Florence, can serve as a vivid example. Take a look through the thick glass at the time, which the man's wrist watch “Anonimo Professionale” (Model 6000) shows us. The automatic movement Anonimo 01.0, assembled on the base of ETA 2814-2 21 and working at 21 stones with a frequency of 28,000 vibrations per hour, providing a power reserve of 40 hours, work hard under the case of this watch. A distinctive feature of this model is a bright green color of the dial. This is particularly surprising, since such bright colors are unusual for military watches, but the brave watchmakers of Anonimo ventured out and created a true masterpiece. The bright dial is provided with the central hour, minute and second hands with luminescent coating, large Arabic numerals, specific to watches in the military style, and the date aperture at "4" hours with a unique magnifying glass. The round thick case of 45 mm in diameter is made of steel AISI316 Plus; the large crown with a reliable security system, patented by Anonimo, is located at an unusual place - at "4" hours. The men's wristwatch from Anonimo is equipped with a rubber strap with steel buckle. The high degree of water protection, 2,000 meters, is provided by a unique water-resistant convex sapphire glass with thickness of as many as 2 mm. This is a fairly high index of glass thickness, which also has a convex shape that makes the Italian men's wristwatch “Anonimo Professionale” (Model 6000) an indispensable time meter, even at great depths under the water column. These men's wristwatches with extra-thick protective glass were produced in a limited edition of 250 pieces.
The 2-mm glass is, of course, the most reliable protection of dial and movement, but the watchmakers do not stop. For example, a colleague of Anonimo, Italian watchmaker “Panerai”, produces men's watches with glass of up to 5 mm in thickness. The Swiss watches “Deep Driver” from the company “Azimuth” with the water resistance of up to 2000 meters are provided with double convex sapphire glass of 4-mm thickness. The list of watches with thick glasses does not end with these models. Moreover, the thickness of glasses is gradually increases. In my opinion, the above models with ultra-thick safety glasses are ones of the most successful and illustrative examples (though not the only). I hope our readers will agree with me that all is fine in measure.

Napoleon’s watch

The bulk of population on our planet tracks the time through the glass of the watches, not even thinking about the fact that the glass on the dial is a truly indispensable tool. Many years ago, at the manufacture of the popular at that time pocket watches, the watchmakers did not use glass, instead the front cover served as a defense for the movement and the dial. According to some historical facts, Napoleon Bonaparte left a deep trace in horlogerie. As a legend goes, once the great military leader, proudly sitting on his horse while hunting (and possibly during the next battle), tried to open the cover of his pocket watch “Blancpain”, which did not want to give in. Losing patience, Napoleon jumped out of the saddle, snatched his sword from the sheath and at one blow cut off the watch’s cover, which dared to disobey him, exactly in half. Later, the watchmakers solved the problem of constant opening and closing the cover in a more civilized way – they inserted a transparent glass into the watch case. However, the case with Napoleon provided the impetus for the creation of the first watch, entitled “demi-savonnete”, which in French literally means "half-open". Returning to this legendary form, "created" by Napoleon, the company “Blancpain” uses it in some of its models (e.g., the Swiss watch “Blancpain Leman “Demi-Savonette” Calendar Moon Phase”, ref. 3563A-3642A-53).

P.S.

Summarizing this article, I would like to remind our dear readers once again that the wristwatch glass is one of the most brilliant (albeit simplest) devices for the watch movement protection. However, glass isn’t armor, so you should not impose huge robust on it and heap burdens on its fragile "shoulders". Experienced watchmaker Konstantin Chaykin from St. Petersburg provides another useful advice to his clients, what to do if the glass is broken into small pieces. Thus, according to the expert, you should immediately stop the mechanical watch (the same applies to quartz) by pressing the seconds stop button. If there is none, you should turn the watch with the dial down, as a sensitive movement might be badly damaged by tiny pieces of glass. In this case, the glass "deserts" from the camp of "defenders" to the camp of "enemies" of the movement. You must be on the alert.
At the beginning of this article, I drew our reader’s attention to the philosophical comprehension of wristwatch glass functions. What is the difference between the time we read through the plexiglass and the time coming into our consciousness through the majestic sapphire? Perhaps, the type of glass is incredibly important, and the degree of this importance depends on the activity of the time meter’s owner (football player, diver, military man, lawyer, etc.). But we shouldn’t forget that, no matter what glass we have on our watches, it cannot affect the general course of time. An endless time river keeps on flowing continually in the right direction, and we have no choice but to follow its course through the glass of our watches.