We were 'Black' last Saturday night, but no sign of any ash on my balcony the next morning. However, every summer we regularly wake up to find everything covered in a thin film of rust-coloured dust- just like brown talcum powder. This is fine dust lifted from the Sahara, so presumably is sand/silica based, and therefore chemically not too far removed from volcanic ash. (I stand to be corrected). How is it that aircraft fly quite happily through this much heavier, and visible, dust concentration without any fuss?