About the grey marble, I painted several layers of dawnstone(GW), administratum grey(GW), and a little ulthuan grey(GW) first.
And add a bit mechanicus standard grey(GW) and dawnstone in 1:1 to the dark area of stone, and several layers of ulthuan grey to make the bright area more brighter.
Then I painted the random lines with abaddon black(GW) and mechanicus standard grey.
