I do not know about the chemicals, but here are some points to consider:
Hesalite
- Will get scratched up easier.
- Is easy/cheap to polish.
- Is cheap to get replaced.
- Does not (to my knowledge) damage the movement, when shattered.
Sapphire
- Will not get scratched (all though they chip off in cases).
- You cannot polish or remove scratches from sapphire.
- Sapphire is relatively expensive to replace.
- When shattered, glass will (very likely) fall into the movement and damage it. The movement will in almost every case need a full service to prevent further damage.
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