How to brighten rocks?

Question

I have some really large boulders around my home, and over the years they've turned from brilliant white, to gray covered in moss. Is there anything I can use to clean them, and make them white again. I thought I'd try bleach but that didn't seem to have any immediate results.

Answer 1

Muriatic acid should etch the surface a bit, and that might expose some fresh rock.

Answer 2

The combo of bleach and a pressure washer will take care of it.

Answer 3

try a pressure washer

Answer 4

bleach and ajax let it sit for a while

Answer 5

you briten roocks with ahcool itthe rubing kind thank you