A minor detail but - I hope - interesting:

In the course of replacing the high dome crystal on a WWII Seiko Phototelemeter stopwatch, I was rather amazed to see that the cracked glass crystal I was replacing had an inner coating of plastic. Much like modern shatter resistant automobile windows. This lamination provides the hard scratch resistant quality of glass with the resilient shatter resistant qualities of plastic.

The composition crystal is rather thin and the plastic is on the inside; unlike automotive glass which is more like a sandwich with plastic in the middle.

The composition crystal appears to be original to the watch, although there is no way of knowing for sure.

It would be interesting to know if this was a Seiko innovation or something Seiko imported.

Although I have replaced a lot of crystals over the years, this is the only laminated crystal I have ever replaced. Are they unusual, or comman?

Best regards,
Greg

Greg,

this is an interesting question to be asked at Seiko directly, they should know...unf i do not have a POC but someone here should....
rgds

Enzo