A brass brush should be used with soapy water. If it is not, the brush can transfer brass particles to the metal. On silver, it would be quite obvious as the metal would have a yellowish cast to it. Rinse the brass brush thoroughly and dry it immediately after using. Soft bristle brass brushes impart a finer, softer finish to metal than soft bristle steel brushes because brass bristles are softer than steel.
Never use a soft bristle steel brush with water as it will rust. Since the bristles on a soft bristle steel brush are stiffer than those on a brass brush, they will leave very fine scratches or grooves in the surface of the metal being brushed. The scratches and grooves are not really noticeable but the metal will have a much less reflective surface than if a brass brush was used. After using, tap the brush handle on the edge of a garbage can, bristles down, to dislodge and remove any particles that may be stuck between the bristles.
Pro Tip: If the brush bristles are softer than the metal being brushed, the brush will polish the metal. If the brush bristles are harder than the metal being brushed, the brush will impart a brushed, satiny finish.
Bristle brush patina tool alternative: Use a clean fine or ultra-fine 3M Scotch Brite pad to buff metal.