The only way to eliminate calculus build up is by brushing and flossing frequently. It takes pyhsical removal of the placque before it calcified into the hard tarter, or calculus. Some people will have more tendency to build up calculus because of the chemical composition of their saliva.
Brasso is a metal polish designed to remove tarnish from brass, copper, chrome and stainless steel. It is available either directly as a liquid or as an impregnated wadding pad.
Our brass ox is more accurately described as a natural brass ox in which a pure brass chain is naturally oxidized, relieved and lacquered to protect the finish. This produces a very rich, bronzy finish. As with any antique finish variations should be expected and is part of what give the chain its antique look.