Button-collectors call that type a brass 1-piece "flatbutton." When the backmark on these says "plated" it always meant the button's front had silver plate. Also at that time in history, "gilt" was the term for gold plating. The version you found dates from 1800 to the mid-1830s. We diggers find brass 1-piece flatbuttons by the handfull along the east coast, from Georgia to Maine, so they are worth about $1 apiece at "relic shows" here in Virginia... but one with a very unusual backmark can bring as much as $5 from a button-backmark collector.