Sorry needed to see the shank at the back ....my best guess is ...
That it appears to be 17th century ..(I have a decent book on id'ing buttons )
the patina looks to be of that age... it will be more recent, say late 18th, if
the pattern is regular making it Machine made ..( earlier you will get parts of the pattern
that are slightly out of sinc ....being hand made ) The best authority on buttons is a certain Brian Read it might be wortwhile if you contact him through
portcullis2@btinternet.com ... you might have a new type ...if not than at least he will tell you more about it ....it might save you some time then trawling through sites ...Regards Mark....