What is a good high gloss coating for polished brass and copper?

they make a specific product to apply to brass.

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Spar varnish is not quite clear, but it has a yellowish tint so it would do well on brass or copper. It is made for boats, so it does have some UV inhibitors that would prolong it's life. It is oil based, so until it drys, there will be an odor. Clear coats do not last as long as coatings that have solids in the formula, so whatever you use, you will be redoing it in a year or two outside, Inside Spar varnish may last 10 years. The sun is the enemy with clear coats.

You can try a clear coat for crafts or clear poly a spray urethane don't know how it would react to brass or if it would even worn if your trying to avoid polishing brass with say brasso or some other type polish use ketchup or taco sauce . Best of luck or look on ehow.com

I use a spray coating meant for photographs and art. What it is, I'm not sure. However, good quality car wax might do what you want, protect it and make it shine. Good old fashioned Johnson paste wax works on guitars and things, so I guess it would work for whatever you want to do, and won't harm other finishes.

Valspar makes a good clear coat.