First use of mineral glass in Omega Constellations?

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A while ago I extended my vintage Constellation collection by acquiring an 18K example with the slimline 712 movement. Although it was designed as a dress watch it is still a full chronometer movement made by Omega, so I figured it had a place in a representative group of Constellations made in the 50s and 60s.

The movement serial number places it in 1968, but unlike all my other Constellations, this 712 is fitted with a mineral glass (or sapphire - I can't tell the difference without scratching it) rather than the usual acrylic, which raised the question of when Omega first used mineral or sapphire glass in production. I confess I was a little surprised, as I had assumed that mineral/sapphire glass was not introduced until the 1970s.

Does anyone have an answer? A few pics for those who are interested.
 
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What is the case number?
 
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Thanks guys. The case back is here. This is a pre cleaning image!
 
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Case calls for sapphire crystal...

062SN5229 | GLASS SAPPHIRE D29 H1.5

Cheers, Al