The bricks on the walkway have what look like dirt stains, lots of irregular
dirty areas. I think it's because the brick hasn't been washed or even
rinsed off(except by the winter rains) for a long time, years. The stains
won't come off with regular washing or brushing and I'd like to know if
there is something, such as acid, that could be used to bring back the
original brick surface. Any suggestions?

John