How best to clean sandstone?

[Rob Morley]

What stone? ;-)

[Andy Dingley]

So what ? It's a sedimentary rock, made of some granular stuff and a binder. Generally the grains are silicaceous and the binder is an iron oxide, but there are plenty of calcareous sandstones around. There are also a few large-grained limestones where, because the grains are visible, they find themselves described as "sandstone" when they're really anything but.