Chimney sweep?

This is an interesting picture/topic.  At the turn of the 1980's I worked at former RAF Turweston.  Being an inquisitive young lad, at the time, I would ask anyone about anything, especially WWII.  One old chap, who said he was stationed on the airfield during wartime, told me that the soil either side of the runways was particularly dark because the local chimney sweep would pour soot onto the runways to prevent them being visible at night due to the moon shine.  Sure enough, in certain areas, the soil is still black to this day, but I've never really believed what I was told even though it was feasible. However, this topic got me thinking!

How did they 'paint' fake hedgerows across these airfields?  What did that use as 'paint'?  Does anyone know?   ......Or, as I have just thought, did they use the soot?  I may be completely barking up the wrong tree here!  Thoughts anyone?