Hmm tricks to cleaning stone?

[apac]

I have a nice slab of red sandstone that's been outside for who knows how long (was here when I bought the house). It's in pretty good shape except that the side I would like to use has been sitting on the dirt for a while, so it's rather dark. Any tricks to cleaning off the dirt stains so it's got the nice red hue again, without harming the stone? Just water doesn't seem to be too effective.

Chemicals?
Drill + steel wool brush bit to grind off a layer?

Eventually I'd like to seal the clean surface and use it as a coffee table.

 

[jmagg]

pressure washer with balls

 

[IronWing]

Is the stone red throughout or is it a surface oxidation layer?

 

[apac]

Is the stone red throughout or is it a surface oxidation layer?

Red throughout. I had to split off some that had eroded away.