I agree wit the problems of using anything acid based. But using something mildly caustic might be you solution. I also would make sure I am not applying to anything highly stressed since you could start a sress/corrosion issue not visible to the eye. Try a strong solution of "simple Green" avaliable at most hardware stores/Home Depot, let it sit for a few minutes, it will brighten it up.

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.