[dddrees]

Originally Posted by Adam K.

As I understand it, the acrylic crystal is pressed into place by the bezel and actually serves the purpose of keeping water out, even though there is no separate gasket beneath it; e.g. the edge of the acrylic crystal pressure set into place keeps moisture from entering through that section of the case---this is why sapphire crystal replacements (which are inflexible, unlike acrylic/plexi) don't work and fail to provide the pressure-proof seal that is so important.

Modern sapphire crystal Rolex models, on the other hand, have a separate gasket (made of Delrin, I believe) which achieves the purpose of keeping moisture from entering. These can shrink and wear over time and UV/heat exposure, and of course should be replaced when needed to keep the watch pressure-proof. With the acrylic crystals, stress cracks can form at the base of the crystal itself due to a strong pressure (severe impact etc) or just dry out over time and begin crazing...which is why on vintage models, the acrylic crystal is typically replaced as a matter of course during a servicing.

Models engineered for the sapphire crystal can use the same crystal indefinitely (assuming its in good shape), as sapphire's properties stay consistent unlike plexi and it is the gasket below which keeps moisture out of these modern references. Slightly different means to achieve the same objective, you can see. But, the disprepancy means acrylic-equipped vintages can't be simply "updated" with a sapphire crystal of any sort...at least if one desires their classic Rolex to retain its water resistant qualities.


Hopefully, this explanation makes sense!

Great explanation Adam, thanks for sharing.