Q: What is the difference between a dome-type windshield and a box-type windshield?
Photograph by Masanori Yoshie
A: The difference between standing up and curved
When reading articles about watches, one thing that often catches your attention is the terms "dome-shaped crystal" and "box-shaped crystal." Both refer to a raised crystal, but there is a slight difference. Seiko defines the two as follows:
-Dual curved sapphire glass (= domed sapphire crystal glass)
"Glass that is curved on both the front and back"
- Box-type sapphire glass (= box-type sapphire crystal windshield)
"Dual curved sapphire glass with a raised outer edge"
According to this definition, a dome-shaped crystal is one that has curves on both the inside and outside, while a box-shaped crystal is one with bulging shoulders. In the Seiko example, fire glass (= sapphire crystal) is mentioned, but the materials used vary, including resin glass (including Plexi), organic glass (including Hardlex), and sapphire crystal.
Pay attention to the gasket on models that use a box-type windshield
In the past, it was very costly to make a box-shaped crystal out of sapphire crystal. For this reason, some manufacturers used dome-shaped crystals. However, with advances in machine tools, more and more models are now using box-shaped sapphire crystal crystals, even in entry-level models. The recent retro style boom is clearly a result of the widespread use of box-shaped sapphire crystal crystals.
When buying a watch with a box-type sapphire crystal, pay attention to the waterproof gasket that supports the crystal. Box-type crystals are heavier than regular crystals, so the waterproof gasket is thicker. Skilled manufacturers hide the white gasket well, but manufacturers that are not used to making watches or hastily made models may have a noticeable gasket between the bezel and the crystal.
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