In rough shape but a Royal Provincial Loyalist Button, RP with a crown above. I'm afraid to clean any more its so brittle. This site keeps producing great relics.
You have saved a Rev War pewter button and now it's fate is in your hands. You may already know this, but it will continue to flake away unless you coat it with something. I have used a thin coat of clear fingernail polish in the past and have also used Elmer's Glue diluted with water. You can practice on any old pewter spoon pieces you have laying around until you find a system that you like.
You just saved a piece of history. You just don't see RP buttons every day! Great job. I have used lite coats of paraffin wax on very brittle buttons with success.