Just a word of caution here. Many objects, not limited to metal and wood, develop color and overall appearance with time. The color is called 'patina.' Patina takes time, and while it can be accelerated artificially, nothing matches color that time brings to an item. Objects with patina are invariably worth more than those whose patina has been removed (lost).

So, if you want bright metal, and do not have an old item whose patina will be lost, or whose monitary value you treasure, or that might some day be sold to somebody who will pay for that patina, by all means use polishing compounds and chemicals.