Try it on a scrap bumper or sumthin first. I have found it does NOT dull the finish. If you don't like it you can always soak it off with plain old household ammonia. I've used it on everything (except tires), even glass, and after 6-7 years on the shelf it hasn't "yellowed". It WILL slightly dull silver or a bare metal finish, but not as much as a clearcoat will. The only drawback I have found is that if you get it wet, it may "cloud up", but will usually straighten out when it dries. I much prefer it over wax or clearcoat, especially for sealing decals.