Tokunaga on: Explanation about the materials of watch glass - Seiko & Citizen Watch Forum – Japanese Watch Reviews, Discussion & Trading
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Old 03-04-2010, 02:09 PM   #1 (permalink)
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Default Tokunaga on: Explanation about the materials of watch glass

Authored by Tokunaga


I understand that Hardlex is used in the Marinemaster due to its shatter resistance. My question is why doesn't Seiko use an acrylic crystal in this case? Acrylic crystals are shatter resistant and unlike Hardlex can be buffed if scratched. Could a Sapphlex crystal be used in this application?


The materials currently used as watch glass and its main characteristics are shown in the following table.

Since the acrylic resin (1) has soft hardness and a heat-resistant temperature is very low, concerning the glass of PROSPEX watches which have high durability performance, such as a MARINEMASTER of this question, we couldn't use acrylic glass in which a lot of scratches and deformation are occurred on the surface.
Although (2) and (3) glass are used by SEIKO with the trademark of "HARDLEX" (glass which raised mechanical intensity by special chemical strengthening processing), they are used for standard watches.
On the other hand, sapphire glass (4) is used abundantly for the dress watches and high-class water-resistant watches and also diver's watches, such as CREDOR and Grand SEIKO and also some PROSPEX watches, such as LANDMASTER watches, SCUBAMASTER diver's watches of SEIKO brand, and hardness and theoretical intensity are excellent, there is also a problem of being unable to make as theoretical strength by the mechanism in destruction of the glass with which a cut angle control is important and a micro crack being detected in microscopic examination in case of large and thick glass.

In SEIKO watches, in addition to the above-mentioned general materials, "High- quality HARDLEX" (the high intensity and highly efficient glass strengthened on (3) Borosilicate glass) and original "SAPPHLEX"(the high cost performance combined glass which adhered thin plate of (4) on (2) or (3) glass) are put in practical use, and those are used according to the aim and specification of the watches.

"High- quality HARDLEX" which is the high intensity and the highly efficient article of the glass are used for the PROSPEX watches and ordinary sports watches. Also "SAPPHLEX" glass is used for the sports watches or the sporty watches,

In case of diver's watch which are required so many characteristics totally, such as resistance to pressure, water resistance, shock resistance, wear resistance, heat resistance, and durability etc., we usually use "High- quality HARDLEX" glass having the most excellent cost performance and sometimes use sapphire glass as a glass of some PROSPEX diver's watches.

Ikuo Tokunaga

Ikuo Tokunaga

Picture credit: Seiko
"That a wristwatch is a small celestial theater. It is a small sky. A device for the measure of shadows." -Gabriel Gudding

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Old 03-04-2010, 05:06 PM   #2 (permalink)
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Default Tokunaga on: sapphire vs Hardlex

Authored by petew

I recently emailed Tokunaga about the use of Sapphire in the new 1000M. His response cleared some misconceptions that I and others have been under the assumption of over the past few years. (Ed now can say "I told you so." )

Here was his very illuminating response to my question: "I see that Seiko will use sapphire glass in the new 1000M diver. Are you now confident that sapphire is a better material than hardlex?"

First of all, if you have misunderstood because of my shortage of explanation at the last glass explanation on the S&C Forum, I must apologize to you for it. What I meant at the explanation is the reason why Seiko has adopted high-quality Hardlex on 1000m professional diver’s watch is that “cost performance is excellent.” I never said that high-quality Hardlex surpasses Sapphire on the performance of the material itself. And I meant that the loss-rate rises high in case of making a larger and thicker Sapphire glass, as a reason the cost of Sapphire is high.

OK, I would explain the meaning more concretely.

The resistance to pressure which SEIKO1000m is virtually asked is at least 2000m or more. High-quality Hardlex of 4mm thickness adopted on 1000m clears this standard. On the other hand, in order to secure the resistance to pressure as same level as that of high-quality Hardlex (4mm) by using Sapphire, the thickness of about 3mm is required. Although both performances are same grade, Sapphire (3mm) is higher about the cost, therefore high-quality Hardlex (4mm) is superior to Sapphire (3mm). -- Incidentally, the thickest Sapphire that SEIKO uses now is less than 3mm. The resistance to pressure of Sapphire (less than 3mm) is inferior to that of high-quality Hardlex (4mm) --

Then, how about the Sapphire of 4mm thickness? Compared with the cost of high-quality Hardlex (4mm), that of Sapphire (4mm) rises very high. However, about the resistance to pressure and the durability of Sapphire (4mm), it exceeds that of high-quality Hardlex (4mm). In order for Sapphire (4mm) to exceed high-quality Hardlex (4mm) also at the point of cost performance, we have needed to reduce the manufacture cost of Sapphire (4mm) further.

In recent years, with producing various kinds of PROSPEX watches, the adoption of Sapphire glass has been promoted, and so many Sapphire glasses of 2mm or more thickness can be manufactured stably. By the improvement of manufacture technology which is related to it, SEIKO has succeeded in reducing the manufacture cost of Sapphire (4mm) to a half of that of 1986. And this time, this Sapphire (4mm) has been carried on new 1000m professional diver’s watch.

One of the key concepts of the SEIKO’s watch making is "The highest cost performance watch in the world." As I mentioned before, SEIKO 1000m professional diver’s watch is one of a few saturation diving specifications watches in the world, and has the highest water-tightness and the air-tightness at a price of about 130,000 yen.

By this time’s model change, user’s cost goes up about 30,000 yen, but I judged that the cost performance of the new model exceeded that of the present model, by considering synthetically the merits, such as the further improvement of resistance to pressure and durability, the materials of the world highest performance, user’s attachment to Sapphire glass, and the other various elements.

At the meaning above, yes, I am confident that Sapphire is better than Hardlex.

Sorry for the long message, but I hope this is helpful for you and other S&C Forumers.
Sincerely yours,

Ikuo Tokunaga

"That a wristwatch is a small celestial theater. It is a small sky. A device for the measure of shadows." -Gabriel Gudding

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