Portland Whitbed is the creamy oolitic limestone of St Paul's Cathedral, Buckingham Palace and Whitehall — the stone that built civic London. In the city's polluted rain-shadows it weathers to soot-black, so a facade reads as fresh cream washed clean against blackened ground. This system inverts the usual light page: it grounds on the authentic weathered patina and lets the carved, shell-flecked stone glow as the highlight, set in Roman inscriptional capitals.