its a standard type 1820ish period british flat button -- gilted (coated with shiny gilt covering") to the "imperal standard"=--- oh ah --- puffed up terms like this were very common on button backs during the early to mid 1800's -- as a sort of "quality boast" --ours are better than theirs because we're "imperial standard " or "trible gilt" or whatever --you get the drift.
value is as little as you'll take for it --as much as they will give for it --went the two "ends" meet thats its "real" worth cash wize -- flat buttons are a rather common find and are not really thought of as high dollar by most folks -- but a cool find historical speaking in the states --in england they tend to think of it as a "trash find" type of item --