When laser marking soft metals like aluminum, brass, bronze, copper, or pewter for best results you should use CerMark LMM 14 coating instead of CerMark LMM 6000. Copper and brass items often have a clear lacquer coating on them to prevent tarnishing. This clear coating will prevent the CerMark from sticking correctly to the metal. Soft metals suck the heat away from the laser area very fast and require slow speed and high power to properly make a mark. Every laser is different so it is important that you test several settings to get the best mark. Make sure you can scrub the mark with a green scrubby sponge or Brillo pad to ensure correct settings.
LMM 14 in liquid form when brushed on has a stronger Ph value and can tarnish the surface of some metals. The spray can form or air brush application dries quickly and should not have this issue.