Peter - Wow, thanks for posting such a great photo!
The answer to your question lies under that amazing layer of coral - not that you would want to remove it, but...
We collectors would look at the details of the lip - its shape says a lot about age. If loosely formed, it could mean an 18th century bottle. If uniformly tooled it would suggest later 19th century.
The base may also help us - specifically the depth and shape of the indent.
Comments
The answer to your question lies under that amazing layer of coral - not that you would want to remove it, but...
We collectors would look at the details of the lip - its shape says a lot about age. If loosely formed, it could mean an 18th century bottle. If uniformly tooled it would suggest later 19th century.
The base may also help us - specifically the depth and shape of the indent.
You might want to take a look at @Harry_Pristis answer in this post:
https://forum.antiquebottles-glass.com/discussion/comment/3241/#Comment_3241
Chris
which has grown since it entered and is now too big to get out.