Possible Clues:

• Solidify; turn into bone
• Become bony
• Outsiders in owners' Shanghai factory become inflexible
• Loss if your houses become inflexible
• Turn to fossil (if fifty were unknown)
• Convert into bone
• Turn to bone with age
• Change into bone, or become unprogressive
• If so, Y's able to get hard like this
• Wartime intelligence agency, for your information, distorted job of bonesetters