Cleaning Oamaru stone

we have a lovely stone statue. In Canterbury it was wonderfully white. here it has turned black. I know it is a soft stone, so don't want to water blast it or put any chemical on it that would react with the stone.

How do I get I back to the nice white stone it used to be

Funny, we were talking about that exact thing waiting to get into the winter gardens on sunday and discussing the cleaning of the white statues there
Apparently wet and forget is best

A few years ago, the council hired someone to clean our soldier at the cenotaph. He is Oamaru stone too. He scraped off years of white paint, taking it back to the bare stone. It doesn't look half as striking as it used to do. I think in this case it would have been better to leave painted

As it's limestone, avoid anything acid, depending on what has stained it, napisan work s well on mould and mildew, try a small patch first.