We would all like to acheive instantly the effects of 1000 years weathering on our new granite - heres a few old wives tales and a few scientific ideas to help you:
Rub Live Yoghurt over all the areas - it must do good!
Gently abrade the surfaces with emery paper to form a key for lichen and rub lichen onto these areas
Use a high nitrogen fertiliser and wash the piece with a solution on a regular basis
Rub soot into the crevices
Place stonework under trees in Autumn
For an instant result try gravy browning
We are always happy to record any ideas you may have